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Volume 95-B, Issue SUPP_28 August 2013 Computer Assisted Orthopaedic Surgery (CAOS) 13th Annual Meeting of CAOS International

J. Dounchis L. Elson C. R. Bragdon D. Padgett M.R. Illgen H Malchau

Introduction

In total hip arthroplasty, the positioning of the acetabular cup, in particular, has been shown to play an important role in the survivorship of the prosthetic joint. The commonly accepted “safe zone” extends from 5–30° of anteversion to 30–50° of inclination. However, several studies have utilized a more restrictive safe zone of 5–25° of anteversion and 30–45° of inclination, a modification of the Lewinnek zone. Many attempts have been made to develop a more reliable method of positioning the acetabular component. Robotic-assisted surgery is one such method. The purpose of this study was to compare the resulting position of the acetabular component after robotic-assisted surgery with the intraoperative robotic data to determine if improved accuracy can be achieved with the robotic-assisted method.

Methods

One hundred and nineteen patients received THA, at four different medical centers in the United States, using a haptic robotic arm. Pre-operative CT scans were obtained for all patients and used during the planning of the procedure, at which point the proposed component size and positioning was determined. Preparation of the acetabular bone bed, as well as impaction of the acetabular component itself, was performed using the robotic device.

Using an AP Pelvis and Cross-Table Lateral radiograph, each patient's resulting acetabular inclination and version was measured using the Hip Analysis Suite software. The component position retrieved from the robot was compared to the measured values from the radiographs. The positioning data was compared to two safe zones described above.


P.S. Walker P.A. Meere C.P. Bell

Obtaining accurate bone cuts based on mechanical axes and ligament balancing, are necessary for a successful total knee procedure. The Orthosensor Tibial Trial displays on a GUI the magnitude and location of the lateral and medial contact forces at surgery. The goal of this study was to develop the algorithms to inform the surgeon which bone cuts or soft tissue releases were necessary to achieve balancing, from an initial unbalanced state.

A rig was designed for lower body specimens mounted on a standard operating table. Surgical Tests were then defined: Sag Test, leg supported at the foot; Dynamic Heel Push test, flexing to 120 degrees with the foot sliding along a rail; Varus-Valgus test; AP Drawer test; Internal-External Rotation test. The bone cuts were made using a Navigation system, to match the Triathlon PCL retaining knee. To determine the initial thickness of the tibial trial, the Sag Test was performed to reach 0 deg flexion. The Heel Push Test was then performed to check the AP position of the lateral and medial contacts, from which the rotational position of the tibial tray was determined. Pins were used to reproduce this position during the experiments.

Surgical Variables were then defined, which would influence the balancing: LCL Stiffness, MCL Stiffness, Distal Femoral Cut Level, Tibial Sagittal Slope, Tibial Varus or Valgus, and AP Femoral Component Length. Balancing was defined as equal lateral and medial forces due to soft tissue tensions throughout the flexion range, equal varus and valgus stiffnesses, and no contacts closer than 10mm to component edges. All of the above tests were then performed sequentially, and the changes in the contact force readings were considered as a signature of that Surgical Variable.

In an actual surgical case, having obtained readings from the Surgical Tests, the data will be compared with the signatures of the Surgical Variables. This will then identify the Variable which needed correction. The Surgical Tests will be repeated and the readings should be closer to balanced. Further correction of another Variable is carried out if necessary. In early clinical cases, it was found that this method allowed for identification of how to reach a balanced state, and achieved soft tissue balancing in a quantitative way.


JG Gerbers PC Jutte

Most types of bone tumor surgery require intra-operative imaging or measurement to control margins and prevent unnecessary bone loss. Computer Assisted Surgery (CAS) has been used as a replacement of fluoroscopy or direct measurement tools in four specific types of oncological orthopaedic surgical approaches. There are intralesional treatments, image-based resections, image-based resections with image-based reconstructions and image-based resections with imageless tumor prostheses reconstruction. Since 2006 we have performed 130 oncological surgeries with CAS.

Most cases were excochleations, 64, where CAS replaces fluoroscopy as an intra-operative imaging modality. Advantages over fluoroscopy are real time three dimensional feedback, high-res image and no use of ionizing radiation. It is especially useful in larger lesions or lesions located in the femoral head or pelvis. Currently a study is being performed on patient satisfaction, recurrence and complications.

Another application where CAS has often been used is in resections and segmental resections (together 45). These can be preplanned before surgery, incorporating the margin required, and checked intra-operatively. Coloration of the tumor, critical structures is useful to avoid these. Sometimes it's possible with careful planning to spare structures that otherwise probably would not confidently have spared.

With hemicortical resection (5) it's possible to use CAS to exactly copy the shape of the resected bone to an allograft. A Ct scan of one case shows an average gap between host and graft of 0.9 mm (range 0–5.4) along the 6 cm resection.

Finally in 16 cases of imageless use in placement of tumor prostheses it feels greatly helpful in reconstructing the joint line, length and correct rotation.

There were 8 failures in these 130 cases with the system or software. Setup time was measured in 47 cases and was on average 6:50 (range 2:26–14:27). Indication and performance of CAS in orthopedic oncology is an under researched aspect of CAS. In our opinion CAS shows great promise in the field of orthopedic oncology and is a valuable tool in the operating room.


T.D. Goldberg W.T. Curry J.W. Bush

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware.

The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland).

In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made.

During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques.

Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7).

Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n=11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°.

Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws, 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal.

The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102).

Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM.

In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA.


T.D. Goldberg W.T. Curry J.W. Bush

The present IRB approved study evaluates the early results of 100 TKAs using CT-based Patient-Specific Instrumentation (PSI) (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). For this technique, a CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made.

Outcomes measured for the present study include surgical factors such as Tourniquet Time (TT) as a measure of surgical efficiency, the actual intraoperative bony resection thicknesses to be compared to the planned resections from the CT scan, and complication data. Furthermore, pre- and post-operative long standing alignment and Knee Society Scores (KSS) were obtained.

During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. No osteophytes are removed as the blocks use the positive topography of the osteophytes for registration. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques.

There were 50 Left and 50 Right TKA's performed in 61 females and 39 males. All patients had diagnosis of osteoarthritis. The average BMI was 31.1 and average age was 64.5 (range 41–90). 79 patients had pre-operative varus deformities with Hip Knee Angle (HKA) average of 174.7° (range 167°–179.5°). 19 patients had pre-operative valgus deformities averaging 184.4° (range 180.5°–190°). Three patients were neutral.

Average TT was 31.2 minutes (range 21–51 minutes). With regard to the bony resections, the actual vs. planned resections for the distal medial femoral resection was 8.7 mm vs. 8.9 mm respectively. Further actual vs. planned femoral resections include distal lateral 7.2 vs. 6.7 mm; posterior medial 8.3 vs. 8.9 mm; and posterior lateral 6.2 vs. 6.8 mm. The actual vs. planned tibial resections recorded include medial 6.4 vs. 6.3 mm and lateral 8.3 vs. 8.2. The planned vs. actual bony cuts are strongly correlated, and highly predictive for all 6 measured cuts (p=<.001). No intraoperative complications occurred.

Average KSS improved from 45.9 to 81.4, and KSS Function Score improved from 57.7 to 73.5 at 6 weeks postoperative visit. There were no thromboembolic complications. Two patients had a post-operative infection requiring surgical intervention.

Post-operative alignment was 179.36° (range 175°–186°) for all patients. Alignment was neutral, within 3° in 95.9% of patients. There were only 4 outliers with maximal post-operative angulation of 6°.

In conclusion, these early results demonstrate efficacy of CT-based PSI for TKA. The surgery can be performed efficiently, accurately, and safely. Furthermore, excellent short term clinical and radiographic results can be achieved.


A. Amir-Khalili R. Abugharbieh A. J. Hodgson

Previously, we demonstrated the effectiveness of phase symmetry (PS) features for segmentation and localisation of bone fractures in 3D ultrasound for the purpose of orthopaedic fracture reduction surgery. We recently proposed a novel real-time image-processing method of bone surface extraction from local phase features of clinical 3D B-mode ultrasound data. We are presenting a computational study and outline of planned future developments for integration into a computer aided orthopaedic surgery framework.

Our image-processing pipeline was implemented on three platforms: (1) using an existing PS extraction C++ algorithm on a dual processor machine with two Xeon x5472 CPUs @ 3GHz with 8GB of RAM, (2) using our proposed method implemented in MATLAB running on the same machine as in (1), and (3) CUDA implementation of our method implemented on a professional GPU (Nvidia Tesla c2050).

We ran these three implementations 20 times each on 128×128×128 scans of the iliac crest in live subjects and repeated the processing for 15 combinations of filter parameters. On average, the C++ implementation took 1.93s per volume, the MATLAB implementation 1.28s, and the GPU implementation 0.08s. Overall, our GPU implementation is between 15 and 25 times faster than the state-of-the-art method.

Implementing our algorithm on a professional grade GPU produced dramatic computational improvements, enabling full 3D datasets to be processed in an average time of under 100ms, which, if proven in a clinical system, would allow for near real time computation. We are currently implementing our algorithm on an open research sonography platform (Ultrasonix Medical Corporation). High-powered graphic cards can easily be integrated into the open architecture of this system, thus enabling GPU computation on diagnostic medical and research ultrasound devices.

We intend to use this platform within a surgical environment for accurate and automatic detection of fractures and as an integral part of our developing computer aided surgery pipeline, in which we use PS features to register intra-operative ultrasound to pre-operative computed tomography images.


S. Weidert P. Wucherer P. Stefan S.P. Baierl M. Weigl M. Lazarovici P. Fallavollita N. Navab

We share our experiences in designing a complete simulator prototype and provide the technological basis to determine whether an immersive medical training environment for vertebroplasty is successful. In our study, the following key research contributions were realised: (1) the effective combination of a virtual reality surgical simulator and a computerised mannequin in designing a novel training setup for medical education, and (2) based on a user-study, the quantitative evaluation through surgical workflow and crisis simulation in proving the face validity of our immersive medical training environment.

Medical simulation platforms intend to assist and support surgical trainees by enhancing their skills in a virtual environment. This approach to training is consistent with an important paradigm shift in medical education that has occurred over the past decade. Surgical trainees have traditionally learned interventions on patients under the supervision of a senior physician in what is essentially an apprenticeship model. In addition to exposing patients to some risk, this tends to be a slow and inherently subjective process that lacks objective, quantitative assessment of performance. By proposing our immersive medical simulator we offer the first shared experimental platform for education researchers to design, implement, test, and compare vertebroplasty training methods.

We collected feedback from two expert and two novice residents, on improving the teaching paradigm during vertebroplasty. In this way, this limits the risks of complications during the skill acquisition phase that all learners must pass through. The complete simulation environment was evaluated on a 5-pt Likert scale format: (1) strongly disagree, (2) disagree, (3) neither agree nor disagree, (4) agree, and (5) strongly agree. When assessing all aspects of the realism of the simulation environment, specifically on whether it is suitable for the training of technical skills team training, the participating surgeons gave an average score of 4.5.

Additionally, we also simulated a crisis simulation. During training, the simulation instructor introduced a visualisation depicting cement extravasation into a perivertebral vein. Furthermore, the physiology of the computerised mannequin was influenced by the instructor simulating a lung embolism by gradually lowering the oxygen saturation from 98% to 80% beginning at a standardised point during the procedure. The simulation was stopped after the communication between the surgeon and the anaesthetist occurred which determined their acknowledgment that an adverse event occurred. The realism of this crisis simulation was ranked with an average score of 4.75.

To our knowledge this is the first virtual reality simulator with the capacity to control the introduction of adverse events or complication yielding a wide spectrum of highly adjustable crisis simulation scenarios. Our conclusions validate the importance of incorporating surgical workflow analysis together with virtual reality, human multisensory responses, and the inclusion of real surgical instruments when considering the design of a simulation environment for medical education. The proposed training environment for individuals can be certainly extended to training medical teams.


Ph. Piriou E. Peronne

Rotational positioning of the femoral component during the realisation of a total knee arthroplasty is an important part of the surgical technique and remains a topic of discussion in the literature. The challenge of this positioning is important because it determines the anatomical result and its effect on the flexion gap and clinical outcome mainly through its impact on patellofemoral alignment. The intraoperative identification of the axis transepicondylar visually or by navigation is not reliable or reproducible. The empirical setting to 3 ° of external rotation, the procedure used to cut or dependent or independent is not adapted to the individual variability of knee surgery. Indeed, the angle formed by the posterior condylar axis and trans-epicondylar axis is subject to large individual variations.

The authors propose a novel technique, using the navigation of the trochlea to determine the rotation of the femoral component. The principle is to consider the rotation of the femoral implant as “ideal” when it makes a perfect superposition of the prosthetic trochlea with the native bony trochlea on patellofemoral view at 60° when planning the femur. The bottom of the prosthetic trochlea is well aligned with the trochlea groove, identified during the trochlear morphing, itself perpendicular to the trans-epicondylar axis. The authors hope to encourage centering patellofemoral joint prosthesis, thus favoring the original kinematics of the extensor apparatus.

The purpose of this study is to demonstrate firstly, that the navigation of the trochlea is a reliable and reproducible method to adjust the rotation of the femoral component relative to the trans-epicondylar axis taken as reference and the other, the rotation control by this method is not done at the expense of the balance gap in flexion.

It is a bi-centric study prospective, nonrandomised, including continuously recruited 145 patients in two French centers. All patients were included in the year 2010 and have all been revised three months and one year of surgery. The average age of patients was 71 years [53, 88]. It was made no selection of patients who have all been included consecutively in the study and in the two centres. In all cases, the rotation of the femoral component was determined by intraoperative navigation of the trochlea. The authors compared the alpha angle (angular divergence between the plane and the posterior bicondylar plane and trans-epicondylar axis) obtained by this method and that calculated on a pre-or postoperative scan. The authors also measured the space between femur and tibia internal and external side in flexion (90°) to assess the impact on the balance in flexion.

There is excellent agreement between the results obtained by the method of CT scan and the trochlear navigation technique. In addition, this technique allows us to achieve a quadrilateral space gap in flexion. The authors found large individual variation in the distal femoral epiphyseal torsion (angle alpha). They demonstrate that the navigation of the trochlea is a reliable and reproducible method to adjust the rotation of the femoral component relative to the trans-epicondylar axis taken as reference and provides, concomitantly, a quadrilateral space gap in flexion.


M.A. Augart J.F. Plate T.M. Seyler S. Von Thaer J. Allen D. Sun G.G. Poehling R.H. Jinnah

Introduction

Unicompartmental knee arthroplasty (UKA) has seen renewed interest in recent years due to improved surgical techniques and prosthetic design, and the desire for minimally invasive surgery. For patients with limited degenerative disease, UKA offers a viable alternative to total knee arthroplasty. Historically, the outcomes of lateral compartment UKA have been inferior to medial compartment UKA, with suboptimal patient satisfaction and increased revision rates. Robotic-assisted UKA has been shown to improve precision and accuracy of component placement, which may improve outcomes of lateral UKA. The purpose of this study was to compare the outcome of robotic-assisted UKA to conventional UKA for degenerative disease of the lateral compartment. The hypothesis of the study was that robotic-assisted lateral UKA results in superior outcomes compared to conventional UKA.

Materials and methods

A search of the institution's joint registry was conducted to identify patients who underwent UKA for limited degenerative disease of the lateral knee compartment. A total of 130 lateral UKAs were identified that were performed between 2004 and 2012. The mean age of the patients was 63.1 years (range, 20 to 88); patients had a mean BMI of 29.9 (range, 18 to 48). The medical records of all patients were reviewed and assessed for the type of surgical procedure used (robotic-assisted versus conventional), length of hospital stay, Oxford knee score, and occurrence of revision surgery.


J.F. Plate M.A. Augart T.M. Seyler D. Sun S. Von Thaer G.G. Poehling J.E. Lang R.H. Jinnah

Introduction

Unicompartmental knee arthroplasty (UKA) has seen renewed interest in recent years and is a viable option for patients with limited degenerative disease of the knee as an alternative to total knee arthroplasty. However, the minimally invasive UKA procedure is challenging, and accurate component alignment is vital to long-term survival. Robotic-assisted UKA allows for greater accuracy of component placement and dynamic intraoperative ligament balancing which may improve clinical patient outcomes. The purpose of this study was to analyse the clinical outcomes in a large, consecutive cohort of patients that underwent robotic-assisted UKA at a single institution with a minimum follow-up of 2 years. The study hypothesis was that robotic-assisted UKA improves patient outcomes by decreasing the rate of revision in comparison to conventional UKA.

Materials and methods

A search of the institutional joint registry was performed to identify patients that underwent robotic-assisted UKA beginning in August 2008. The patients' electronic medical record was analysed for surgical indication, age at surgery, body mass index (BMI), and American Society of Anesthesiology Physical Status Classification System (ASA). Patient comorbidities were evaluated using the Charlson comorbidity index. Length of surgery and length of hospitalisation were assessed and clinical outcomes were evaluated using the Oxford Knee Score. In addition to postoperative follow-up assessments in clinic, patients without recent follow-up were contacted by telephone to capture the overall revision rate and time to revision.


J. Kooyman A.J. Hodgson

Introduction

Bracing, a strategy employed by humans and robotic devices, can be generally described as a parallel mechanical link between the actor, the environment, and/or the workpiece that alters the mechanical impedance between the tool and workpiece in order to improve task performance. In this study we investigated the potential value of bracing in the context of bone milling to treat cam-type femoroacetabular impingement (FAI) lesions. The goal of this study was to evaluate whether a proposed bracing technique could enable a user to perform a cam resection more accurately and quickly than a currently employed arthroscopic technique.

Materials/Methods

Test samples consisted of white urethane plastic reproductions of a commercially available adult proximal femur, which were laser scanned to obtain ground-truth surface information. A black cam lesion was then cast onto the surface of the femur in the anterosuperior region of the femoral neck, creating a clear visual resection boundary for the simulated osteochondroplasty. Test subjects were 4 adult males (25 +/− 3 years) with no surgical experience. Test conditions included two binary factors: (1) Braced vs. Unbraced – The braced case introduced a spherical bearing tool support mounted in the approximate anterolateral arthroscopic portal position. (2) Speed vs. Accuracy – The subject was instructed to perform the resection as quickly as possible or as accurately as possible with a moderate regard for time. Following the removal of the lesion, femurs were laser scanned to acquire the post-resection surface geometry, with accuracy being reported as RMS deviation between the pre- and post-resection scans over the anterosuperior neck region.


J. Eschweiler M. Asseln P. Damm G. Al Hares G. Bergmann M. Tingart K. Radermacher

Musculoskeletal loading plays an important role in the primary stability of THA. There are about 210,000 primary THA interventions p.a. in Germany. Consideration of biomechanical aspects during computer-assisted orthopaedic surgery is recommendable in order to obtain satisfactory long-term results. For this purpose simulation of the pre- and post-operative magnitude of the resultant hip joint force R and its orientation is of interest. By means of simple 2D-models (Pauwels, Debrunner, Blumentritt) or more complex 3D-models (Iglič), the magnitude and orientation of R can be computed patient-individually depending on their geometrical and anthropometrical parameters. In the context of developing a planning module for computer-assisted THA, the objective of this study was to evaluate the mathematical models. Therefore, mathematical model computations were directly compared to in-vivo measurements obtained from instrumented hip implants.

With patient-specific parameters the magnitude and orientation of R were model-based computed for three patients (EBL, HSR, KWR) of the OrthoLoad-database. Their patient-specific parameters were acquired from the original patient X-rays. Subsequently, the computational results were compared with the corresponding in-vivo telemetric measurements published in the OrthoLoad-database. To obtain the maximum hip joint load, the static single-leg-stance was considered. A reference value for each patient for the maximum hip load under static conditions was calculated from OrthoLoad-data and related to the respective body weights (BW).

On average there are large deviations of the results for the magnitude (Ø=147%) and orientation (Ø=14.35° too low) of R obtained by using Blumentritt's model from the in-vivo results/measurements. The differences might be partly explained by the supplemental load of 20% BW within Blumentritt's model which is added to the input parameter BW in order to consider dynamic gait influences. Such a dynamic supplemental load is not applied within the other static single-leg-stance models. Blumentritt's model assumptions have to be carefully reviewed due to the deviations from the in-vivo measurement data.

Iglič's 3D-model calculates the magnitude (Ø17%) and the orientation (Ø49%) of R slightly too low. For the magnitude one explanation could be that his model considers nine individual 3D-sets of muscle origins and insertion points taken from literature. This is different from other mathematical models. The patient-individual muscle origin and insertion points should be used.

Pauwels and Debrunner's models showed the best results. They are in the same range compared to in-vivo data. Pauwels's model calculates the magnitude (Ø5%) and the orientation (Ø28%) of R slightly higher. Debrunner's model calculates the magnitude (Ø1%) and the orientation (Ø14%) of R slightly lower.

In conclusion, for the orientation of R, all the computational results showed variations which tend to depend on the used model.

There are limitations coming along with our study: as our previous studies showed, an unambiguous identification of most landmarks in an X-ray (2D) image is hardly possible. Among the study limitations there is the fact that the OrthoLoad-database currently offers only three datasets for direct comparison of static single leg stance with in-vivo measurement data of the same patient. Our ongoing work is focusing on further validation of the different mathematical models.


G. Alhares J. Eschweiler K. Radermacher

Knee biomechanics after total knee arthroplasty (TKA) has received more attention in recent years. One critical biomechanical aspect involved in the workflow of present TKA strategies is the intraoperative optimisation of ligament balancing. Ligament balancing is usually performed with passive flexion-extension in unloaded situations. Medial and lateral ligaments strains after TKA differ in loaded flexion compared to unloaded passive flexion making the passive unloaded ligament balancing for TKA questionable. To address this problem, the development of detailed and specific knowledge on the biomechanical behavior of loaded knee structures is essential. Stress MRI techniques were introduced in previous studies to evaluate loaded joint kinematics. Previous studies captured the knee movement either in atypical loading supine positions, or in upright positions with help of inclined supporting backrests being insufficient for movement capture under full body weight-bearing conditions.

In this work, we proposed a combined MR imaging approach for measurement and assessment of knee kinematics under full body weight-bearing in single legged stance as a first step towards the understanding of complex biomechanical aspects of bony structures and soft tissue envelope. The proposed method is based on registration of high resolution static MRI data (supine acquisition) with low resolution data, quasi-static upright-MRI data (loaded flexion positions) and was applied for the measurement of tibio-femoral kinematics in 10 healthy volunteers. The high resolution MRI data were acquired using a 1.5T Philips-Intera system, while the quasi-static MRI data (full bodyweight-bearing) was obtained with a 0.6T Fonar-Upright™ system. Contours of femur, tibia, and patella from both MRI techniques were extracted using expert manual segmentation. Anatomical surface models were then obtained for the high resolution static data.

The upright-MRI acquisition consisted of Multi-2D, quasi-static sagittal scans each including 4 slices for each flexion angle. Starting with full knee extension, the subjects were asked to increase the flexion in 4–5 steps to reach the maximum flexion angle possible under space and force limitations. Knees were softly padded for stabilisation in lateral-medial direction only in order to reduce motion artifacts. During the upright acquisition the subjects were asked to transfer their bodyweight onto the leg being imaged and maintain the predefined flexion position in single legged stance. The acquisition at every flexion angle was obtained near the scanner's isocenter and takes ∼39 seconds.

The anatomical surface models of the static data were each registered to their corresponding contours from the weight-bearing scans using an iterative closest point (ICP) based approach. A reference registration step was carried out to register the surface models to the full extension loaded position. The registered surfaces from this step were then considered as initial conditions for next ICP registration step. This procedure was similarly repeated to ensure successful registrations between subsequent flexion acquisitions.

The tibio-femoral kinematics was calculated using the joint coordinate system (JCS). The combined MR imaging approach allows the non-invasive measurement of kinematics in single legged stance and under physiological full weight-bearing conditions. We believe that this method can provide valuable insights for TKA for the validation of patient-specific biomechanical models.


H.E. Fakhfakh G. Llort-Pujol C. Hamitouche E. Stindel

INTRODUCTION

Over the last twenty years, image-guided interventions have been greatly expanded by the advances in medical imaging and computing power. A key step for any image-guided intervention is to find the image-to-patient transformation matrix, which is the transformation matrix between the preoperative 3D model of patient anatomy and the real position of the patient in the operating room. In this work, we propose a robust registration algorithm to match ultrasound (US) images with preoperative Magnetic Resonance (MR) images of the Humerus.

MATERIALS AND METHODS

The fusion of preoperative MR images with intra-operative US images is performed through an NDI Spectra® Polaris system and a L12-5L60N TELEMED® ultrasound transducer. The use of an ultrasound probe requires a calibration procedure in order to determine the transformation between an US image pixel and its position according to a global reference system.

After the calibration step, the patient anatomy is scanned with US probe. US images are segmented in real time in order to extract the desired bone contour. The use of an optical measurement system together with trackers and the previously-computed calibration matrix makes it possible to assign a world coordinate position to any pixel of the 2D US image. As a result, the set of US pixels extracted from the images results in a cloud of 3D points which will be registered with the 3D Humerus model reconstructed from MR images.

The proposed registration method is composed of two steps. The first step consists of US 3D points cloud alignment with the 3D bone model. Then, the second step performs the widely-known Iterative Closest Point (ICP) algorithm. In order to perform this, we define the coordinate system of both the 3D Humerus model and the US points cloud. The frame directions correspond to the directions of the principal axes of inertia calculated from the matrices of inertia of both the preoperative 3D model and the US data obtained intra-operatively. Then, we compute the rotation matrix to estimate the transformation between the two coordinate systems previously calculated. Finally the translation is determined by evaluating the distance between the mass centres of the two 3D surfaces.


A. Ferretti F. Conteduca D. Mazza B. Maestri G. Bolle G. Argento A. Redler R. Iorio

Introduction

In total knee arthroplasty extramedullary tibial guides could not to be as accurate as requested in obtaining proper alignment perpendicular to the mechanical axis. The aim of this study was to determine the accuracy of an accelerometer-based system (KneeAlign 2; OrthAlign Inc, Aliso Viejo, California) as evaluated by post-op X-rays analysis.

Methods

Between March 2012 and May 2012 thirty consecutive patients with primary gonarthrosis were selected for unilateral total knee arthroplasty (TKA) using a handheld surgical navigation system to perform the tibial resection.

Navigation procedure: The entire system is provisionally secured to the tibia using a spring placed around the leg and is fixed to the proximal aspect of the tibia using 2-headed pins. Before fixing the system proximally, an aiming arm is used to align the top of the device with the anterior cruciate ligament footprint and the medial one third of the tibial tubercle. Distally, a footplate connected to the tibial jig is used to keep the EM jig a set distance off of the tibial surface. A gyrometer within the navigation unit is then able to calculate the posterior slope of the tibial jig. Subsequent anatomical landmarkings of both the lateral and medial malleoli are identified using the distal aspect of the EM jig to establish the tibia's mechanical axis. Similarly, the gyrometer within the navigation unit is able to calculate the varus or valgus alignment of the tibial jig relative to the tibia's established mechanical axis. Once anatomical registration has been performed, the tibial cutting block is placed at the proximal aspect of the device, and real-time feedback is provided by the navigation unit to the surgeon, who is then able to set the cutting block's varus/valgus and posterior slope alignment before performing the tibial resection.

Postoperatively, standing anteroposterior hip-to-ankle radiographs and lateral knee-to-ankle radiographs were performed to determine the varus/valgus alignment and the posterior slope of the tibial components relative to the mechanical axis in both the coronal and sagittal planes. The difference between the intraoperative reading of the tibial varus/valgus alignment and posterior slope provided by the system was compared to the radiographic measurements obtained postoperatively for each respective case. Differences were analysed via standard t test. The critical level of significance was set at P <0.05.


A. Ferrett C. D'Arrigo E. MOonaco B. Maestri F. Conteduca

Introduction

The Segond's fracture is described as a cortical avulsion of the lateral tibial plateau at the site of insertion of the middle third of the lateral capsular ligament. The Segond's fracture is usually associated with a tear of the Anterior Cruciate Ligament (ACL) and it is considered as an indirect radiological sign of complete rupture of the ACL. However there are no studies investigating the effect of a Segond's fracture on the kinematic of the knee especially on the rotatory instability and Pivot Shift (PS) phenomenon. The purpose of this study is to investigate the effect of a Segond's fracture on the kinematic of the knee with the use of navigation and the PS test.

Methods

Ten whole fresh-frozen cadavers were used. A navigator (2.0 Orthopilot Navigation System, BBraun Aesculap, Tuttlingen, Germany) was used to measure maximum manual Anterior Tibial Translation (ATT) at 30°, 60° and 90° of flexion, maximum manual Internal Rotation (IR) and maximum manual External Rotation (ER) at 0°, 15°, 30°, 45° and 90° of flexion. All procedures were performed three times and the mean value taken as the final result in each case. Moreover a PS test was performed by the senior, most experienced, surgeon, and graded as mild (gliding), moderate (jerk) and severe (subluxation). Navigation measurements and PS tests were performed in each knee with ACL intact, after arthroscopic cutting of the entire ACL and after a Segond's fracure was produced by exposing the antero lateral compartment of the knee underneath the ileo-tibial tract. Statistical analysis was performed using ANOVA 1-way and MANOVA tests and value for statistical analysis was set at p<0.05


A. Ferretti R. Iorio D. Mazza L. Caperna G. Bolle G. Argento F. Conteduca

Introduction

The aim of this study is to investigate the accuracy and reliability of a Magnetic Resonance Imaging (MRI) based Patient Match Technology (PMT) system (VISIONAIRE, Smith & Nephew, Inc, Memphis, Tenn) by intraoperative use of VectorVision knee navigation software from BrainLAB (Redwood City, California, USA).

Methods

Between February 2011 and May 2011, 15 patients with primary gonarthrosis were selected for unilateral Total Knee Arthroplasty (TKA). The first three patients were excluded from this study, as they were considered as a warm up to set up the procedure. Therefore 12 patients entered the study. Preoperatively all patient underwent a full-length weight-bearing radiograph in antero-posterior (AP) and a MRI according to the protocol suggested and approved by the manufacturer. All patients were operated with cemented posterior stabilised prosthesis cruciate ligament sacrificing (Journey BCS, Smith & Nephew, Inc, Memphis, Tennessee, USA) by the same surgeon using the VISIONAIRE patient matched cutting jigs. During surgery, once the guides were placed and fixed, the orientation was checked by the navigator. The following parameters were evaluated: size of the implant, alignment in coronal and sagittal plane. An unsatisfactory result was considered an error ≥ 2° in both plane for each component as a possible error of 4° could result in aggregate.


M. Asseln F. Zimmermann J. Eschweiler K. Radermacher

Currently, standard total knee arthroplasty (TKA) procedures focus on axial and rotational alignment of the prosthesis components and ligament balancing. Even though TKA has been constantly improved, TKA patients still experience a significantly poorer functional outcome than total hip arthroplasty patients.

Among others, complications can occur when knee kinematics (active/passive) after TKA do not correspond with the physiological conditions. We hypothesised that the Q-angle has a substantial impact on active joint kinematics and should be taken into account in TKA. The Q-angle can be influenced by the position of the tibial tuberosity (TT). A pathological position of the TT is commonly related to patellofemoral pain and knee instability. A clinically well accepted surgical treatment is the TT medialisation which causes a change in the orientation of the patella tendon and thus alters the biomechanics of the knee. If active and passive knee kinematics differs, this aspect should be considered for implant design and positioning. Therefore we investigated the sensitivity of active knee kinematics related to the position of the TT by using a complex multi-body model with a dynamic simulation of an entire gait cycle.

The validated model has been implemented in the multi-body simulation software AnyBody and was adapted for the present issue. The knee joint is represented by articulating surfaces of a standard prosthesis and contains 6 degrees of freedom. Intra-articular passive structures are implemented and the muscular apparatus consists of 159 muscles per leg. As input parameter for the sensitivity analysis, the TT was translated medially 9 mm and laterally 15 mm from the initial position in equidistant steps of 3 mm.

The Q-angle was about 10° in the initial position, which lies in the physiological range. It changed approximately 2.5° with a gradual shift of 3 mm, confirming the impact of the individual TT position on active knee kinematics. The tibiofemoral kinematics, particularly the internal/external rotation of the tibia was significantly affected. Lateralisation of the TT decreased the external rotation of the tibia, whereas a medialisation caused an increase. During contralateral toe off the external rotation was +7.5° for a medial transfer of 9 mm and −1.4° for a lateral transfer of 15 mm, respectively. The differences in external rotation were almost zero for low flexion angles, correlating with the activation pattern of the quadriceps muscle: the higher the activation of the quadriceps, the greater were the changes in kinematics.

In conclusion, knee kinematics are strongly affected by the Q-angle which is directly associated with the position of the TT. As active kinematics may show significant differences to passive kinematics, intraoperative ligament balancing may result in a suboptimal ligament situation during active motion. Since the Q-angle varies widely between gender and patients, the individual situation should be considered. The optimisation of the model and further experimental validation is one aspect of our ongoing work.


Z. Dib G. Dardenne N. Poirier P.Y. Huet C. Lefevre E. Stindel

INTRODUCTION

In orthopedic surgery, the lower limb alignment defined by the HKA parameter i.e. the angle between the hip, knee and ankle centers, is a crucial clinical criterion used for the achievement of several surgeries. It can be intraoperatively determined with Computer Assisted Orthopedic Surgery (CAOS) systems by computing the 3D location of these joint centres. The hip centre used for the computation of the HKA is defined by the experts as the anatomical centre of the femoral head. However, except for Total Hip Replacement procedure, the hip joint is not accessible and the hip center is computed using functional methods. The two most common are the Least Moving Point (LMP) and the Pivoting (PIV).

MATERIALS AND METHODS

We have analysed on six cadaveric lower limbs the intra-observer variability of both the anatomical and the functional hip centres. The differences between the HKAs angle obtained with the anatomical hip centre (HCANAT) and those obtained with the functional hip centres coming from the LMP (HCLMP) and the PIV (HCPIV) algorithms have also been analysed.


P. Sriphirom C. Siramanakul B. Chanopas S. Boonruksa T. Chompoosang S. Wonglertsiri C. Uthaicharatratsame

Gap planning in total knee arthroplasty (TKA) navigation is critically concerned. Osteophyte is one of the contributing factors for gap balancing in TKA. The osteophyte is normally removed before gap planning step. However, the posterior condylar osteophyte of femur is sometimes removed during the flexion gap preparation or may not be removed at all depends on individual case. This study attempts to investigate on how posterior condylar osteophyte affects on gap balancing and limb alignment during operation.

The study was conducted on 35 varus osteoarthritis knees with posterior condylar osteophyte and undergone on TKA navigation. All knees were measured by CT scan for the size of posterior condylar osteophyte according to its width. Extension gap, flexion gap width, and limb alignment were measured by using the tension device with distraction force of 98 N on both medial and lateral sides under computer assisted surgery. The measuring of extension gap, flexion gap width, and limb alignment was undertaken before and after the posterior condylar osteophyte removal.

This study reveals that the mean of the size of posterior condylar osteophyte after removal is 8.96 mm. The posterior condylar osteophyte has an effect on the increasing of medial extension gap and lateral extension in average 0.74 ± 0.72 mm. and 0.42 ± 0.67 mm. respectively. It also increases 0.71 ± 1.00 mm. in medial flexion gap and 0.97 ± 1.47 mm. in lateral flexion gap. After the posterior condylar osteophyte removal the mean of varus deformity is decreased 0.90° ± 1.14 ° while the mean of extension angle of sagittal limb alignment is increased 1.61°±1.69°. There is also a significant relationship between the size of posterior condylar osteophyte and the increasing of lateral flexion gap and also with the varus deformity decreasing. If the size of posterior condylar osteophyte is increased 10 mm. the lateral flexion gap will be increased 1.15 mm. and varus deformity will be decreased 0.75 degree.


M. Kunz J.F. Rudan S. Mann R. Twiss R.E. Ellis

Introduction

Computer-assisted methods for acetabulum cup navigation have shown to be able to improve the accuracy of the procedure, but are time-consuming and difficult to use. The goal of this project was to develop an easy-to-use navigation technique, requiring minimal equipment for acetabular cup alignment.

Material

A preoperative CT scan was obtained, a 3D model of the acetabulum was created, the pelvic plane determined and the cup orientation planned. A registration area, which included the accessible part of the acetabular fossa and the surrounding articular surface, was chosen for the individualised guide. A guidance cylinder, aligned along the planned cup orientation, was attached in the centre of the guide.

To transfer the planned alignment information from the registered guide to the impacting of the cup, we developed an intraoperative guidance method based on inertia sensors. The sensors were aligned orthogonal to the central cylinder of the patient-specific guide and the orientation was recorded. At the time of impacting the cup, the sensors were attached to the impactor and the surgeon used the recorded information for the alignment of the impactor.


M. Kunz D. Bardana J. Stewart

Introduction

Osteochondral autologous autograft (also called mosaic arthroplasty) is the preferred treatment method for very large osteochondral defects in the ankle. For long-term success of this procedure, the transplanted plugs should reconstruct the curvature of the articular surface. The different curvatures between femoral-patella joint and the dome of the talus makes the reconstruction difficult and requires lots of experience.

Material

Prior to the surgery a CT arthrogram of the ankle, as well as a CT of the knee were obtained and 3D bone models for the knee, the ankle as well as a model for the ankle cartilage were created. Using custom-made software a set of osteochondral grafts (“plugs”) positioned over the defect site were planned and an optimal harvest location for each plug was chosen.

Intraoperatively, an optoelectronic navigation system was installed and sensors were attached to femur, talus, and conventional harvest and delivery chisels. A combined pair-point and surface matching was performed to register femur and talus.

For each planned plug the surgeon positioned, oriented, and rotated the harvest and delivery chisels with respect to preoperative plan by using the visual and numerical feedback of the system.


S.V. Joshi P.J. Rowe G. Pierce K.E. Ahmed C. MacLeod C.J. Whitters

Over the last decade Computer Assisted Orthopaedic Surgery (CAOS) has emerged particularly in the area of minimally invasive Uni-compartmental Knee Replacement (UKR) surgery. Image registration is an important aspect in all computer assisted surgery including Neurosurgery, Cranio-maxillofacial surgery and Orthopaedics. It is possible for example to visualise the patient's medial or lateral condyle on the tibia in the pre-operated CT scan as well as to locate the same points on the actual patient during surgery using intra-operative sensors or probes. However their spatial correspondence remains unknown until image registration is achieved. Image registration process generates this relationship and allows the surgeon to visualise the 3D pre-operative scan data in-relation to the patient's anatomy in the operating theatre.

Current image registration for most CAOS applications is achieved through probing along the articulating surface of the femur and tibial plateau and using these digitised points to form a rigid body which is then fitted to the pre-operative scan data using a best fit type minimisation. However, the probe approach is time consuming which often takes 10–15 minutes to complete and therefore costly. Thus the rationale for this study was to develop a new, cost effective, contactless, automated registration method which would entail much lesser time to produce the rigid body model in theatre from the ends of the exposed bones. This can be achieved by taking 3D scans intra-operatively using a Laser Displacement Sensor.

A number of techniques using hand held and automated 3D Laser scanners for acquiring geometry of non-reflective objects have been developed and used to scan the surface geometry of a porcine femur with four holes drilled in it. The distances between the holes and the geometry of the bone were measured using digital vernier callipers as well as measurements acquired from the 3D scans. These distances were measured in an open source package MESHLAB version 1.3.2 used for the interpretation, post-processing and analysis of the 3D meshes. Absolute errors ranging from of 0.1 mm to 0.4 mm and the absolute percentage errors ranging from 0.48% to 0.75% were found. Additionally, a pre-calibrated dental model was scanned using a 650 nm FARO™ Laser arm using the global surface registration approach in Geomagic Qualify package and our 3D Laser scanner. Results indicate an average measurement error of 0.16 mm, with deviations ranging from 0.12mm to −0.13 mm and a standard deviation of 0.2 mm. We demonstrated that by acquiring multiple scans of the targets, complete 3D models along with their surface texture can be developed. The overall scanning process, including time required for the post-processing of the data requires less than 20 minutes and is a cost-efficient approach. Moreover, the majority of that time was used in post processing the acquired data which could be potentially reduced through the use of bespoke application software. This project has provided proof of concept for a new automated, non-invasive and cost efficient registration technique with the potential of providing a quantitative assessment of the articular cartilage integrity during lower limb arthroplasty.


P. Sriphirom T. Chompoosang M. khongphaophong P. Churasiri

Few previous studies showed that the conventional total knee replacement (TKR) has affection to the same side of talar tilt (TT). We expected to prevent this problem by the computer-assisted (CAS) TKR. The purpose of this study was to compare between pre and post-operative talar tilt and ankle clinical assessment on the CAS TKR and the Conventional TKR in 28 patients (56 knees) whom underwent bilateral TKR.

28 patients, 56 knees, whom underwent both CAS total knee replacement (TKR) and conventional total knee replacement (TKR), in both knees, with the combination of Gap Balance and Measurement Resection techniques performed by one surgeon (P. Sriphirom) at Rajavithi Hospital, Bangkok. The post-operative has a 12 months follow-up for ankle radiographic finding by tibiotalar angle (TTA), tibial articular surface angle (TAS), and talar tilt (TT) = (TAS-TTA) and for ankle clinical assessment by foot functional index (FFI) from pre-operation and post-operation from both groups. The study also compares the CAS TKR with the Conventional TKR for pre-operation and post-operation.

56 knees, 28 patients, mean age = 67.79 years whom underwent bilateral TKR by the Conventional group and the CAS group had pre-operative TT (TT = TAS − TTA). The Conventional group = 1.5 (−5, 8), the CAS group = 0.5 (−5, 8), P value = 0.65. On post-operative TT the Conventional group = 0.0 (−5, 3), the CAS group = 1.0 (−3, 8), the P value = 0.4. The comparison of pre-operative TT and post-operative TT in the Conventional group, the P value = 0.01. On pre-operative TT and post-operative TT in the CAS group, the P value = 0.65. TT was significantly different in the Conventional group but was not significantly different in the CAS group. The ankle clinical assessment by foot functional index (FFI), which are (1) Pain, (2) Difficulty living, and (3) Daily life activity limitation. The pre-operative FFI in the Conventional group = 1.85 (0.81, 6.88) and pre-operative FFI in the CAS group = 1.91 (0.24, 66.5), the P value = 0.57. The post-operative FFI in the Conventional group = 1.68 (0.24, 7.0) and post-operative FFI in the CAS group = 1.65 (0.24, 6.76), the P value = 0.04, which showed a significantly different between the post-operative FFI from both groups. In the Conventional group the post-operative FFI was not significantly different from pre-operative FFI, the P value = 0.2 but for the CAS group the post-operative FFI was not significantly different from pre-operative FFI, the P value = 0.04.

This study showed that the conventional TKR effected to post-operative talar, tilt but CAS TKR has less effect and was not significantly different to ankle joint. Finally, the study needs to be conducted on more patients and to be observed on a longer term follow-up.


E. Lugez D.R. Pichora S.G. Akl R.E. Ellis

Recently, electromagnetic tracking for surgical procedures has gained popularity due to its small sensor size and the absence of line-of-sight restrictions. However, EM trackers are susceptible to measurement noise. Indeed, depending on the environment, measurement uncertainties may vary considerably. Therefore, it is important to characterise electromagnetic measurement systems when used in a fluoroscopy setting. The purpose of our study is to assess decoupled static electromagnetic measurement errors in position and orientation, without adding potential interference, in the presence of fluoroscopic imaging equipment.

Using an Aurora electromagnetic tracking system (Northern Digital, Waterloo, Canada), 5 degrees of freedom measurements were collected in a working space located midway between the source and the receiver of a flat-panel 3D fluoroscope (Innova 4100, GE Healthcare, Buc, France) emitting X-rays. In addition, to determine potential EM distortion from X-rays, electromagnetic measurement accuracies, as a function of position, were compared before, during, and after X-ray emissions. To decouple position and orientation errors, two scaffold devices were designed. Their centre was placed approximately at X = −50, Y = 0, and Z = −300 mm in the EM tracker's global coordinate system. First the positioning scaffold was used to assess the position and orientation measurement uncertainties as a function of position. Next, the orienting scaffold was used to assess the position and orientation measurement uncertainties as a function of orientation. Then, a least-squares method was employed to register the path position measurements to the known geometry of the scaffolds. As a result, the position accuracy was defined as the Euclidean distance between the registered and the ground truth positions. Finally, the orientation accuracy was defined as the difference between two direct angles: the angle between two measured consecutive paths, and the angle of the corresponding ground truth.

When translating the sensor using the positioning scaffold, the resulting position accuracy was characterised by a mean of 3.2 mm. Similarly, when rotating the sensor using the orienting scaffold, the resulting orientation accuracy was characterised by a mean of 1.7 deg. As for the “cross-displacement” errors, the orientation accuracy as a function of position had a mean of 1.8 deg. Likewise, the position as a function of orientation had a mean of 4.0 mm. Position and orientation accuracies – as a function of position, before, during, and after emission of X-rays – indicate that there was no significant interference by the presence of an X-ray beam on the EM measurements.

This work provides evidence that placing the EM system into X-ray beams does not affect EM measurement accuracies. Nevertheless, the fluoroscope itself significantly increases the EM measurement errors. Careful analysis of the EM measurement distribution errors suggests that associated uncertainties are predictable and preventable. In essence, EM tracking is promising for orthopedic procedures that may require the use of a fluoroscope.


A. Billaud A. Moreau-Gaudry D. Girardeau-Montaut F. Billet D. Saragaglia P. Cinquin

Direct arthroscopic cartilage assessment remains the gold standard. It is recommended by the International Cartilage Repair Society (ICRS) to systematically assess cartilage status during arthroscopy but this examination is highly subjective, poorly reproducible, time-consuming and lacks precision. US has shown good potential for cartilage evaluation but is limited in extra-articular conditions. It is also difficult to manually maintain a perfect perpendicularity between the ultrasound beam and the curved surface of the cartilage. Therefore, we have developed a navigated intra-articular US probe (NIAUS). The NIAUS probe could contribute to a more exhaustive and direct intra-articular evaluation of cartilage integrity. Navigation enables control of the US echo pulse perpendicularity and its localisation relative to the joint. Our objectives were (1) to evaluate automatic cartilage thickness measurement with the NIAUS probe in comparison to high definition MRI on cartilage samples, (2) to generate a real-time 3D map of the thickness parameter on samples, and (3) to demonstrate the feasibility of a full NIAUS probe cartilage scan on a specimen distal femur in arthroscopic conditions.

The NIAUS probe is a 4.5mm probe consisting of a 64 element linear array transducer with a central frequency of 13 MHz and a motorised head. The NIAUS probe is navigated. The rotating US head position is controlled by navigation in order to enable constant perpendicular acquisition of cartilage. The NIAUS probe thickness measurement (1) was evaluated on bone and cartilage samples of 9 tibial plateaus. The cartilage thickness was measured via automatic segmentation. Each sample was also scanned in a high resolution MRI (4,7 Tesla) and cartilage thickness was semi-automatically extracted for comparison. During NIAUS scan, (2) a visual 3D map was generated. Finally (3), we scanned two distal femurs with the NIAUS probe in arthroscopic navigated conditions on one specimen and a 3D map of the distal femur thickness was generated in real time.

NIAUS thickness measurement (1) absolute error compared to MRI for 9 plateaus ranged from 0.15mm to 0.32mm in median, p25=0.07 and 0.18, p75=0.28 and 0.5 respectively. 3D maps of the sample cartilage thickness (2) were generated in real time during the NIAUS scan. The cadaveric procedure (3) was conducted without incident via the two anterior portals and a 3D map of the distal femurs cartilage thickness was generated.

A precise US arthroscopic grading and scoring of cartilage during surgery could help for better standardisation, prediction of results and making “live” decisions. Our in vitro experiment shows good results compared to MRI for NAIUS cartilage thickness measurement, and our cadaveric study demonstrate the feasibility of a NIAUS scan in arthroscopic conditions. Our results are encouraging and a clinical trial is currently being designed for preliminary in vivo NIAUS evaluations of cartilage thickness compared to MRI.


A. Niesche A. Korff M. Müller M. Mirz C. Brendle S. Leonhardt K. Radermacher

Total hip replacement is one of the standard procedures in orthopedic surgery. Due to various reasons revision surgery (RTHR) has to be performed. In case of the revision of a cemented prosthesis stem, the bone cement has to be removed from the femoral cavity.

Conventionally the cement removal is done manually using a hammer, chisel or burr under X-ray control, causing a considerable radiation exposure for patient and the surgeon. Furthermore the risk of undesirable bone damage is high due to bad sight and access conditions, leading to complications and prolongation of the intervention. Different approaches addressing the mentioned problems were proposed, but did not achieve acceptance in clinical practice due to disadvantages concerning process controllability. Another possibility is to use a robot guided milling tool. However, to be able to control it typically a 3D reconstruction of the cement volume to be removed is necessary. Existing approaches use computed tomography based measurements combined with previously implanted markers, fluoroscopy or ultrasound based measurements, all requiring additional process steps prior to the surgery or to the actual cement removal.

The ICOS project (Impedance Controlled Surgical Instrumentation, Chair of Medical Engineering, RWTH Aachen University) investigates the approach of electrical impedance controlled, robot assisted bone cement removal, based on real time cement detection during the removal process without radiation exposure or the necessity of prior imaging or marker implanting steps. Therefore the electrical impedance is measured between the milling head mounted on the surgical mini-robot MINARO and one or more electrodes attached to the skin of the patient's thigh. An impedance variation mainly results from decreasing thickness of bone cement near the milling head contact point due to material removal. Hence the proposed method does not generate a 3D volume allowing for a milling path generation prior to the process. It requires a strategy for real time path generation using only the limited local information. Up to now, only the differentiation between bone cement and bone, and thus the cement-bone interface breakthrough, is reliably detectable. To efficiently use this information for the tool path generation, generic a-priori knowledge of the bone cement shape after removal of the prosthesis stem is used.

The concept for impedance controlled milling has been verified in first lab trials. For impedance measurements during the cement removal process the robots milling tool has been modified to achieve electrical insulation of the milling head. A strategy for online adaptive robot path planning has been implemented and tested in a Matlab/Simulink based process simulation. For all data sets a cement removal rate of about 90% with a bone removal of approximately 3% was achieved. These results confirm that it is generally possible to use only the limited local information for automated cement removal. Future work aims for a practical evaluation of the algorithm using real impedance measurement values.

This work has been funded by the German Ministry for Education and Research (BMBF) in the framework of the ICOS project under grant No. BMBF 13EZ1005.


M. Karia M. Masjedi B. Andrews Z. Jaffry J. Cobb

Barriers to the adoption of unicompartmental knee arthroplasty (UKA) by new consultants could be explained by its higher revision rate, to which mal-positioned components contribute. The aim of this study was to determine whether robotic technology enables inexperienced surgeons to perform accurate UKAs when compared to current conventional methods

After randomisation, sixteen trainees who had never performed UKAs performed three medial UKAs (Corin Uniglide), one per week, on dry-bone simulators by either robotic (Sculptor RGA) or conventional methods. They were instructed to match a universal 3D-CT based pre-operative plan that would result from a UKA based on the conventional jigs and operating guide. The knees were laser scanned and software used to compare the planned and actual implant positions. Feedback was given to trainees between attempts. Translational and rotational positioning errors were measured in all six degrees of freedom for both components

At all attempts robotic medial UKAs were more accurate in both translational and rotational alignments for both components reaching statistical significance (p<0.005) at all attempts for rotational errors. Considering outliers, the maximum rotational errors of the robot group was 9° and 7° for the tibial and femoral components respectively. For the conventional group this reached 18° and 16° for the tibial and femoral components respectively

Robotic technology allows inexperienced surgeons to perform medial UKAs on dry bone models with acceptable accuracy and precision on their first attempt. Conventional jigs do not. The adoption of robotic technology might provide new consultants with the confidence to offer UKAs to their patients by limiting the inaccuracies inherent in conventional equipment.


R Rambani W Viant J Ward AMMA Mohsen

Surgical training has been greatly affected by the challenges of reduced training opportunities, shortened working hours, and financial pressures. There is an increased need for the use of training system in developing psychomotor skills of the surgical trainee for fracture fixation. The training system was developed to simulate dynamic hip screw fixation. 12 orthopaedic senior house officers performed dynamic hip screw fixation before and after the training on training system. The results were assessed based on the scoring system that included the amount of time taken, accuracy of guide wire placement and the number of exposures requested to complete the procedure. The result shows a significant improvement in amount of time taken, accuracy of fixation and the number of exposures after the training on simulator system. This was statistically significant using paired student t-test (p-value <0.05).

Computer navigated training system appears to be a good training tool for young orthopaedic trainees The system has the potential to be used in various other orthopaedic procedures for learning of technical skills aimed at ensuring a smooth escalation in task complexity leading to the better performance of procedures in the operating theatre.


A. Amir-Khalili R. Abugharbieh A.J. Hodgson

Background

Previously, we demonstrated the effectiveness of phase symmetry (PS) features for segmentation and localisation of bone fractures in 3D ultrasound for the purpose of orthopedic fracture reduction surgery. We recently proposed a novel real-time image-processing method of bone surface extraction from local phase features of clinical 3D B-mode ultrasound data. We are presenting a computational study and outline planned future developments for integration into a computer aided orthopedic surgery framework.

Methods

Our image-processing pipeline was implemented on three platforms: (1) using an existing PS extraction C++ algorithm on a dual processor machine with two Xeon x5472 CPUs @ 3GHz with 8GB of RAM, (2) using our proposed method implemented in MATLAB running on the same machine as in (1), and (3) CUDA implementation of our method on a professional GPU (Nvidia Tesla c2050).


M. Mayya S. Poltaretskyi C. Hamitouche J. Chaoui

INTRODUCTION

Automated MRI bone segmentation is one of the most challenging problems in medical imaging. To increase the segmentation robustness, a prior model of the structure could guide the segmentation. Statistical Shape Models (SSMs) are efficient examples for such application. We present an automated SSM construction approach of the scapula bone with an adapted initialisation to address the correspondences problem. Our innovation stems from the derivation of a robust SSM based on Watershed segmentation which steers the elastic registration at some critical zones.

METHODS

The basic idea is to relate only corresponding parts of the shape under investigation. A sample from the samples set is chosen as a common reference (atlas), and the other samples are landmarked and registered to it so that the corresponding points can be identified. The registration has three levels: alignment, rigid and elastic transformations.

To align two scapulae, we define a coordinate system, attach it to each scapula and align both systems. For this, we automatically locate three characteristic points on the scapula's surface. All samples are then scaled to the atlas and the rigid registration is determined by minimising the Euclidian distance between surfaces using Levenberg-Marquadt algorithm.

Afterwards, the samples are locally deformed toward the atlas using directly their landmarks (traditional approach). Unfortunately, landmarks-correspondences could be mismatched at some anatomically complex, “critical,” zones of the scapula. To overcome such a problem, we suggest to 3D-segment these “critical” zones using a 3D Watershed-based method.

Watershed is based on a physical concept of immersion, where it is achieved in a similar way to water filling geographic basins. We believe that this is a natural way to segment the surface of the scapula since it has two large “basins”: the glenoid and the subscapularis fossa. Watershed is followed by geometrical operations to establish eight separated zones on the surface of the scapula.

Once we have the zones, surface-to-surface correspondence is defined and the landmarks' point-to-point correspondences are obtained within each zone pair separately. The elastic registration is then applied on the whole surface via a multi-resolution B-Spline algorithm. The atlas is built through an iterative procedure to eliminate the bias to the initial choice and the correspondences are identified by a reverse registration. Finally, the statistical model can be constructed by performing Principle Component Analysis (PCA).


M. Akbari Shandiz S.K. Saevarsson S. Yoo C. Anglin

Knee kinematics are altered by total knee arthroplasty (TKA) both intentionally and unintentionally. Knowledge of how and why kinematics change may improve patient outcome and satisfaction through improved implant design, implant placement or through rehabilitation.

In the present study we imaged and compared the 6 degree-of-freedom (DOF) patellofemoral (PF) and tibiofemoral (TF) kinematics of 9 pre-TKA subjects to the kinematics of 15 post-TKA subjects (Zimmer NexGen LPS implants) using a novel sequential-biplanar radiographic protocol that allowed imaging the postoperative patellofemoral joint under weightbearing throughout the range of motion, which has not been done previously to our knowledge.

There were clear, statistically significant differences between the pre-TKA and post-TKA kinematics: for the TF joint, the tibia was more posterior and inferior (max 20 mm and 15 mm, respectively) in the post-TKA group compared to the pre-TKA group (p<0.001), and had neutral alignment in the post-TKA group compared to varus alignment (max 9°) in the pre-TKA group (p<0.001). For the PF joint, the patella was shifted more posteriorly and medially, and tilted more medially in the post-TKA group compared to the pre-TKA group (p<0.001). There were no significant differences in PF superior/inferior translation and flexion/extension (p>0.5). Both groups showed differences from normal kinematics, based on the literature.

The kinematic differences are likely due to a combination of surgical, implant and patient factors. To investigate this further, we imaged the 9 pre-TKA subjects a minimum one year after their surgery; analysis of these data is in progress. Computed tomography (CT) scans and quality of life surveys were also taken before and after surgery. By comparing the preoperative and postoperative kinematics and shape for the same subjects, and analysing the interrelationships amongst these, we aim to determine if a different implant shape or different component positioning could create more normal kinematics, resulting in a better clinical outcome.


A.J. Blair-Pattison J.L. Henke J.G. Penny R.W. Hu G. Swamy C. Anglin

Inserting screws into the vertebral pedicles is a challenging step in spinal fusion and scoliosis surgeries. Errors in placement can lead to neurological complications. The more experienced the surgeon, the better the accuracy of the screw placement. A physical training system would provide residents with the feel of performing pedicle cannulation before operating on a patient. The proposed system consists of realistic bone models mimicking the geometry and material properties of typical patients, coupled with a force feedback probe. The purpose of the present study was to determine the forces encountered during pedicle probing to aid in the development of this training system.

We performed two separate investigations: [1] 15 participants (9 expert surgeons, 3 fellows and 3 residents) were asked to press a standard pedicle awl three times onto a mechanical scale, blinded to the force, demonstrating what force they would apply during safe pedicle cannulation and during unsafe cortical breach; [2] three experienced surgeons used a standard pedicle awl fitted with a one-degree of freedom load cell to probe selected thoracolumbar vertebrae of eight cadaveric specimens to measure the forces required during pedicle cannulation and deliberate breaching. A total of 42 pedicles were tested.

Both studies had wide variations in the results, but were in general agreement. Cannulation (safe) forces averaged approximately 90 N (20 lb) whereas breach (unsafe) forces averaged approximately 135–155 N (30–35 lb). The lowest average forces in the cadaveric study were for pedicle cannulation, averaging 86 N (range, 23–125 N), significantly lower (p<0.001) than for anterior breach (135 N; range, 80–195 N); medial breach (149 N; range, 98–186 N) and lateral breach (157 N; range, 114–228 N). There were no significant differences between the breach forces (p>0.1). Cannulation forces were on average 59% of the breach forces (range, 19–84%) or conversely, breach forces were 70% higher than cannulation forces.

To our knowledge, these axial force data are the first available for pedicle cannulation and breaching. A large range of forces was measured, as is experienced clinically. Additional testing is planned with a six-degree-of-freedom load cell to determine all of the forces and moments involved in cannulation and breaching, throughout the thoracolumbar spine. These results will inform the development of a realistic bone model as well as a breach prediction algorithm for a physical training system for spine surgery.


J.Y.Y. Chu R. Easteal P. St. John M. Kunz J. Rudan

Metal-on-metal hip resurfacing arthroplasty (MoMHRA) has been a popular alternative treatment for young patients with hip osteoarthritis. Despite its advantages over total hip arthroplasty, the use of MoMHRA remains controversial. Achieving the correct positioning of the prosthetic is a concern due to the difficulty and novelty of this procedure. Furthermore, it has been reported that post-operative management using 2D radiographs contains high degrees of variance leading to poor detection of prosthetic malpositioning. In order to compensate for the lack of available technology, current literature has suggested the use of blood metal ion levels as indirect predictors of prosthetic malpositioning due to the abnormal release of metal ions, particularly Chromium and Cobalt, as a result of increase wear and tear. The purpose of this study was to determine whether 2D/3D registration technology can report prosthetic orientation in vivo and, to establish whether 3D technology can accurately deduce prosthetic wear by correlating prosthetic angles with metal ion counts.

To begin this study, post-operative x-rays (n=72) were used as the two-dimensional media to measure acetabular orientation. Only the acetabular component was examined in this study and acetabular orientation was defined as the function of inclination and version angles. Virtual three-dimensional models of the native, pre-operative pelvises and the acetabular implant were generated and were manually superimposed over the post-operative x-ray images according to anatomical landmarks. A manual 2D/3D registration program was specifically designed for this task. Inclination and version angles of the 2D/3D registered product were measured. Post-operative CT models, which offer the most accurate depiction of the prosthetic in vivo, were generated for validation. Contrary to the study's hypotheses and current literature, no significant difference was observed between 2D vs. 2D/3D vs. CT data, suggesting that 2D and 2D/3D measurements were similar to the results of the gold standard CT model (although 2D/3D measurements were more precise compared to 2D media). Furthermore, statistical analyses revealed no significant correlation in either 2D or 2D/3D compared to metal ion levels, although a stronger trend was demonstrated using 2D/3D measurements. These results are suggestive that 2D/3D registered measurements are equivocal to those using the conventional 2D x-ray and, manual 2D/3D registered measurements do not demonstrate greater efficacy in predicting prosthetic wear. Moreover, the data from this study also revealed insignificant correlations between the angles of acetabular orientation and metal ion release. Combined angles within and beyond the acceptable ranges for inclination (30°–50°) and version (5°–20°) angles did not produce significant trends with metal ion release. These results lead to the paradoxical conclusion that acetabular orientation does not influence prosthetic wear. The findings of this study are inconsistent with the reports in current literature and further investigation is required.


Kyoung Jai Lee Eun Kyoo Song Jong Keun Seon Hyeong Won Park Cheol Park

The purpose of this study was to compare intraoperative varus-valgus laxities in total knee arthroplasty [TKA] using either a single-radius femoral design or multi-radius femoral design.

56 TKAs were performed by using a single radius femoral design (Scorpio NRG, SR group) and 59 TKAs were performed by using a multi-radius femoral design (Zimmer NexGen, MR group), both with a minimum of 1-year follow-up. We compared intra-operative varus-valgus laxities at 0°, 30°, 60°, 90° of flexion using the navigation system (Orthopilot, Aesculap, Tuttlingen, Germany). A series of clinical outcomes were evaluated at the time of the latest follow-up including HSS, WOMAC, VAS score during stair climbing.

At 30°, 60° of flexion, the mean total varus-valgus laxities in SR group (6.2 ± 3.5° at 30° of flexion and 6.8 ± 1.5° at 60° of flexion) were significant less than those in MR group (9.2 ± 4.3° at 30° of flexion and 8.3 ± 3.8° at 60° of flexion) (p=0.027 and p=0.042, respectively). In the clinical results, there was not significant difference.

The single-radius femoral designs for TKA showed evidently less intra-operative mid-flexion stability compared with the multi-radius femoral design. However clinical outcomes revealed no other significant dissimilarity on HSS, WOMAC and VAS scores during stair climbing.


Jong Keun Seon Eun Kyoo Song Hyeong Won Park Kyoung Jai Lee Cheol Park

The purpose of this study was to compare the laxity, radiological and clinical outcomes of TKA that performed using the navigation system and using the conventional technique at least 10-year follow-up.

47 navigational TKAs and 45 conventional TKAs were included for this study. Varus-valgus laxities were measured on the stress radiographs. The radiological measurements with regard to the mechanical axis, the inclination of the femoral and tibial components, femoral posterior condylar off-set difference and radiolucency were compared. The clinical evaluations were performed using ROM, WOMAC and KS score.

There was no significant difference in the total laxity. However, more than 10° of total laxity was significantly reduced in the navigation group (1 knee in the navigation group and 6 knees in the conventional group). The mean of mechanical axis was not statistically different between two groups. But, the outlier numbers of mechanical axis in the two groups was significantly different. The difference in ROM was not observed between the two groups. HSS, WOMAC, KS scores were significantly better in the navigation group.

The navigation system can provide good stability, improved alignment accuracy of the lower extremity and better clinical results compared with conventional technique.


Jong Keun Seon Eun Kyoo Song Kyoung Jai Lee Hyeong Won Park Cheol Park

We hypothesised that the excellent alignments achieved in UKA using a navigation system(NA-MIS UKA) would improve mid-term clinical results versus UKA without a navigation system(MIS-UKA). The clinical results and the component alignment accuracies of NA-MIS UKA and MIS UKA were compared after a minimum follow-up of five years.

56 UKAs in the navigation group and 42 UKAs in conventional group were included. The radiological measurements with regard to the mechanical axis, the inclination of the femoral and tibial components, and radiolucent line or loosening were evaluated and compared between two groups. The clinical evaluations were performed using ROM, WOMAC, HSS and pain score.

A significant inter-group difference was found in terms of WOMAC or HSS, pain scores. In the sagittal inclination of the femoral and tibial components, radiolucent line, there were no statistical differences between two groups. However, the outlier numbers at mechanical axis, the mean of coronal inclination of the femoral and tibial component in the two groups was significantly different.

The navigation system in UKA can provide improved alignment accuracy of the lower extremity, also there were significant differences in functional outcomes after 5 year-follow-up.


Cheol Park Eun Kyoo Song Jong Keun Seon Hyeong Won Park Kyoung Jai Lee

We undertook this study to compare the flexion stabilities, the clinical outcomes, and complications in cases of TKA using either the robotic technique (ROB-TKA) or navigation-assisted technique (NA-TKA).

Robot group (53 knees) and navigation group (56 knees) that underwent TKA for osteoarthritis were assessed for varus and valgus laxity at 90° of knee flexion after a minimum three-year follow-up. These evaluations included KS, WOMAC scores, and ROM. To evaluate flexion stability, varus and valgus laxities at 90° of knee flexion were measured using stress radiographs.

KS and WOMAC scores were significantly improved at last follow-up. However, no significant difference was found between the ROB-TKA and NA-TKA groups for any clinical outcome parameter. No significant intergroup differences were found in mechanical axis or coronal alignments and the mean varus laxities. No significant difference was found for varus-valgus imbalance at 90° of knee flexion. Complications differed in the two groups but none of the cases were severe enough to warrant a revision.

Both robotic and navigation assisted TKAs were found to restore good coronal leg and prosthesis alignments and good flexion stabilities. However, clinical knee scores and flexion stabilities were no better in short term for robot assisted TKA than for navigation assisted TKA.


A.V. Kaminsky E.V. Gorbunov

Introduction

Stryker computer navigation system has been used for total knee arthroplasty (TKA) procedures since October 2008 at the Russian Ilizarov Scientific Centre for Restorative Traumatology and Orthopaedics.

Material and methods

There have been 126 computer assisted TKA that accounted for 11.5 % of primary TKA within this period (1096 procedures). Arthritis of the knee joints with evident pain syndrome was an indication to TKA surgery. Arthritis of the knee joint of 27 patients (21.4 %) was accompanied by femoral deformity of various etiology with debris found in the medullary canal in several cases. The rest 99 patients (78.6 %) were regular cases of primary TKA.


J. Chaoui G. Walch P. Boileau

INTRODUCTION

The glenoid version assessment is crucial step for any Total Shoulder Arthroplasty (TSA) procedure. New methods to compute 3D version angle of the glenoid have been proposed. These methods proposed different definitions of the glenoid plane and only used 3 points to define each plane on the 3D model of the scapula. In practice, patients often come to consultation with their CT-scans. In order to reduce the x-ray dose, the scapulae are often truncated on the inferior part. In these cases, the traditional scapula plane cannot be calculated. We hypothesised that a new plane definition, of the scapula and the glenoid, that takes into account all the 3D points, would have the least variation and provide more reliable measures whatever the scapula is truncated or not. The purpose of the study is to introduce new fully automatic method to compute 3D glenoid version for TSA preoperating planning and test its results on artificially truncated scapulae.

MATERIAL AND METHODS

Volumetric preoperative CT datasets have been used to derive a surface model shape of the shoulder. The glenoid surface is detected and a 3D version and inclination angle of the glenoid surface are computed. We propose a new reference plane of the scapula without picking points on the 3D model. The method is based on the mathematical skeleton of the scapula and the least squares plane fitting. Specific software has been developed to apply the plane fitting in addition the automatic segmentation process. An orthopedic surgeon defined the traditional scapular plane based on 3 points and applied the measures on 12 patients. The manual process has been repeated 3 times and the intra-class correlation coefficient (ICC) was calculated to compare the results with our automatic method. To validate the reliability of the new plane relating to truncated scapulae, we have measured the 3D orientation variation on 37 scapulae. Nine iterations have been applied on each scapula by cutting 5mm of the scapular inferior part.


T.M. Ecker S.D. Steppacher M. Haimerl S.B. Murphy

Introduction

Correct postoperative leg length restoration is among the most important goals of hip arthroplasty. Therefore, we developed, validated and clinically applied a novel software algorithm based on surgical navigation, which allows the surgeon to restore a defined femur position without establishing a femoral coordinate system or the hip joint center and measure the leg length accurately and simply.

Material and Methods

This new leg length algorithm was used in 154 hips (145 patients) that underwent CT-based computer-assisted THA (VectorVision Build 274 prototype; BrainLAB AG, Helmstetten, Germany) with a tissue preserving superior capsulotomy. Intraoperatively, a pelvic and a femoral dynamic reference bases (DRB) were applied and the anterior pelvic plane (APP) was set as the pelvic coordinate system. Then, the hip joint was put in a neutral position and this position, and the relative position of the femoral DRB relative to the pelvic DRB, was captured and stored by the navigation system. After implantation of the prosthesis the same above described femoral position with the same amplitude of flexion/extension, abduction/adduction and rotation was restored. Now, any resulting difference was due to linear changes. Validation of this new algorithm was performed by comparing the navigated results to measurements from calibrated antero-posterior pre- and postoperative radiographs. The radiographic results were compared to the mean leg length change measured with the navigation system.


W.S. Murphy J.H. Kowal S.B. Murphy

Introduction

Conventional methods of aligning the acetabular component during hip arthroplasty and hip resurfacing often rely upon anatomic information available to the surgeon. Such anatomical information includes the transverse acetabular ligament and the locations of the pubis, ischium and ilium. The current study assesses the variation in orientation of the plane defined by the pubis, ischium and ilium on a patient-specific basis as measured by CT.

Methods

To assess the reliability of anatomical landmarks in surgery, we assessed 54 hips in 51 patients (32 male, 22 female) who presented for CT-based surgical navigation of total hip arthroplasty. From a 3D model of each patient, standardised points for the anterior pelvic plane and landmarks on the ilium, ischium, and pubis were entered. The plane defined by the anatomical landmarks was calculated in degrees of operative anteversion and operative inclination according to the definitions of Murray.


W.S. Murphy J.H. Kowal S.B. Murphy

Introduction

Cup malposition in hip arthroplasty and hip resurfacing is associated with instability, accelerated wear, and the need for revision. The current study similarly assesses the variation in cup position using conventional techniques as measured by CT.

Methods

We have performed CT-based navigation of hip arthroplasty and revision arthroplasty on a routine basis since 2003 and also use CT imaging to quantify periprosthetic osteolysis. In our image database, we have identified 91 hips in 87 patients (51 female, 36 male) who had a previously conventionally-placed cup on CT imaging. For each hip, cup orientation was determined in operative anteversion and operative inclination (according to the definitions of Murray) using an application specific software application (HipSextant Research Application 1.0.7, Surgical Planning Associates Inc., Boston, Massachusetts). This application allows for determination of the Anterior Pelvic Plane coordinates from a 3D surface model. A multiplanar reconstruction module allows for creation of a plane parallel with the opening plane of the acetabulum and subsequent calculation of plane orientation in the AP Plane coordinate space.


W.S. Murphy S.D. Werner J.H. Kowal S.B. Murphy

Introduction

The optimal acetabular component orientation in general or on a patient-specific basis is currently unknown. In order to answer this question, the current study uses CT to assess acetabular orientation in a group of unstable hips as compared to a control group of stable hips.

Methods

Our institutional database of CT studies performed in the region of the hip beginning in February of 1998 (41,975 CT studies) was compared against our institutional database of revision total hip arthroplasties beginning in August of 2003 (2262 Revision THA) to identify CT studies of any hip treated for recurrent instability by revision of the acetabular component. Twenty hips in 20 patients with suitable CT studies were identified for the study group. Our control group consisted of 101 hips in patients who had CT studies either for computer-assisted surgery on the contralateral side or for assessment of osteolysis. Using the CT data, the AP plane (APP) was defined, supine pelvic tilt was measured, and cup orientation was calculated by fitting a best fit plane to 6 points on the rim of the acetabular component. Cup orientation was calculated in degrees of operative anteversion and operative inclination according to the definitions of Murray. Both absolute cup position relative to the APP and tilt-adjusted cup position were calculated.


B. Sankar K. Deep M. Changulani S. Khan S. Atiya A. Deakin

INTRODUCTION

Leg length discrepancy following total hip arthroplasty (THA) can be functionally disabling for affected patients and can lead on to litigation issues. Assessment of limb length discrepancy during THA using traditional methods has been shown to produce inconsistent results. The aim of our study was to compare the accuracy of navigated vs. non navigated techniques in limb length restoration in THA.

METHODS

A dataset of 160 consecutive THAs performed by a single surgeon was included. 103 were performed with computer navigation and 57 were non navigated. We calculated limb length discrepancy from pre and post op radiographs. We retrieved the intra-operative computer generated limb length alteration data pertaining to the navigated group. We used independent sample t test and descriptive statistics to analyse the data.


M.s. Khan l.z. Jilani k. Deep

Introduction

Malalignment of lower limb is a common feature in patients with osteoarthritis (OA). This, either cause or effect of OA, is known to alter the normal anatomy of knee and affects progression of wear and tear in mechanically stressed compartment. We investigated the relationship of mechanical axis to wear and tear in varus, neutral and valgus knees.

Materials and Methods

A retrospective analysis of 136 consecutive patients, with OA, who underwent total knee replacement using computer navigation. The thickness of medial and lateral cuts of distal femur and proximal tibia were recorded. Pre-op coronal deformity was assessed using long leg radiographs and Femoral Tibial Mechanical Angle (FTMA) calculated. Patients were evaluated as one group and three subgroups based on preop varus, neutral or valgus lower limb alignment. Student t test and Pearson's correlation coefficient were used for statistical analysis.


K. Deep M.S. Khan S. Goudie

Introduction

Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the precision and accuracy of computer navigation system in predicting cup placement and restoring limb length and offset.

Material and Methods

An analysis of 259 consecutive patients who had THA performed with imageless computer navigation system was carried out. All surgeries were done by single surgeon (KD) using similar technique. Acetabular cup abduction and anteversion, medialisation or lateralisation of offset and limb length change were compared between navigation measurements and follow-up radiographs. Precision, accuracy, sensitivity and specificity were calculated to assess navigation for cup orientation and student t-test used for evaluation of offset and limb length change. A p value of <0.05 was considered significant for evaluation.


K. Deep

Introduction

Malalignment of cup in total hip replacement (THR) increases rates of dislocation, impingement, acetabular migration, pelvic osteolysis, leg length discrepancy and polyethylene wear. Many surgeons orientate the cup in the same anteversion and inclination as the inherent anatomy of the acetabulum. The transverse acetabular ligament (TAL) and acetabular rim can be used as a reference. No study has yet defined the exact orientation of the TAL. The aim of this study was to describe the orientation of acetabular margin and compare it with TAL orientation.

Materials and Methods

Sixty eight hips with osteoarthritis undergoing THR with computer navigation were investigated. Anterior pelvic plane was registered using anterior superior iliac spines and pubic symphysis. Orientation of the natural acetabulum as defined by the acetabular rim with any osteophytes excised was measured. Since TAL is a rectangular band like structure, three recordings were done for each corresponding to the outer middle and inner margin of the band. All the readings were given by software as radiological anteversion and inclination.


S.A.C. Sampath H.S. Voon M. Sangster H. Davies

Background

Recent publications have supported the anatomic placement of anterior cruciate grafts to optimise knee function. However, anatomic placement using the anteromedial portal has been shown to have a higher failure rate than traditional graft placement using the transtibial method. This is possibly due to it being more technically difficult and to the short femoral tunnel compromising fixation methods. It also requires the knee to be in hyper flexion. This position is not feasible during with a tourniquet in situ on the heavily muscled thighs of some athletes.

Hypothesis: That navigation can be used to place the femoral tunnel in the anatomic position via a more medial transtibial tunnel.

Methods

25 patients underwent Navigated Anterior Cruciate reconstruction with quadruple hamstring grafts. The Orthopilot™ 3.0 ACL (BBraun Aesculap, Tuttlingen) software was used. The femoral and tibial ACL footprints were marked on the bones with a radio frequency probe and registered. The pivot shift test, anterior drawer and internal and external rotation were registered. A navigated tibial guide wire was inserted at 25° to the sagittal plane and 45° to the transverse plane exiting through the centre of the tibial footprint. The guide wire was advanced into the joint to just clear of the surface of the femoral footprint with the knee in 90° flexion. Flexion/extension of the knee was done to determine the closest position of the guide wire tip to the centre of the anatomical femoral footprint. If the tip was within 2mm of the centre of footprint, the position was accepted. If not the tibial guide wire was repositioned and the process repeated. The tibial tunnel was drilled, followed by transtibial drilling of the femoral tunnel. A screen shot was done to allow determination of the shape and area of the tunnel aperture relative to the femoral footprint using ImageJ (National Institute of Health). The graft was fixed proximally with an Arthrex ACL Tightrope® and distally with a Genesys™ interference screw. The pivot shift test, anterior drawer and internal and external rotation were repeated and recorded using the software.


S.A.C. Sampath H.S. Voon M. Sangster H. Davies

Introduction

Total knee arthroplasty has become an established operation. Cemented fixation of the components has given satisfactory results and is accepted as the gold standard. Cement failure with aseptic loosening, however, is a possible long term complication. This is particularly important in view of the increasing number of younger patients who can benefit from this procedure. Hence the attraction of using implants fixed by direct osseointegration of bone into the implant, by passing the potential weak link of the cement.

Objectives

The objective of this study was to determine the mid-term clinical, radiological and functional outcomes after navigated cementless and cemented implantation of total knee arthroplasties without patella resurfacing done by a single surgeon.


S.A.C. Sampath S. Lewis M. Fosco D. Tigani

Introduction

Wolff's Law proposes that trabecular bone adapts in response to mechanical loading and that trabeculae align with the trajectory of predominant loads. The current study is aimed to investigate trabecular orientation in the tibia in patients with osteoarthritis of the knee. Consistent with Wolff's Law, it was hypothesised that orientation would reflect the mechanical loading of the joint and hence that there would be a correlation between the trabecular orientation and the mechanical axis of the lower limb.

Methods

51 anonymised radiographs from patients with osteoarthritis were analysed using ImageJ (National Institute of Health). Each patient had both a standard anteroposterior radiograph of the knee and a long leg view taken while weight bearing.

For each anteroposterior radiograph, the angle of the femoral shaft and tibial shaft were measured. The femoral shaft – tibial shaft (FS -TS) angle was then calculated as the difference between the two, as described by Sheehy et al. (2011). A medial rectangle was selected with the top, bottom, medial and lateral borders being the sclerotic bone, the growth line, the bone edge and the centre of the medial tibial spine. Corresponding measurements were done on the lateral side. Trabecular orientation of both areas was measured using OrientationJ (an ImageJ plugin). In all cases the medial and lateral orientation angles were expressed relative to the angle of the tibial shaft.

The mechanical axis of the lower limb was measured from the full length radiographs by calculating the angle formed by the femoral and tibial axes, as described by Goker and Block. All measurements were done independently by two observers, SAS and SL.


H. Ren W. Liu S. Song

Surgical navigation systems enable surgeons to carry out surgical interventions more accurately and less invasively, by tracking the surgical instruments inside human body with respect to the target anatomy. Currently, optical tracking (OPT) is the gold standard in surgical instrument tracking because of its sub-millimeter accuracy, but is constrained by direct line of sight (LOS) between camera sensors and active or passive markers. Electromagnetic tracking (EMT) is an alternative without the requirement of LOS, but subject to environmental ferromagnetic distortion. An intuitive idea is to integrate respective strengths of them to overcome respective weakness and we aim to develop a tightly-coupled method emphasising the interactive coupled sensor fusion from magnetic and optical tracking data. In order to get real-time position and orientation of surgical instruments in the surgical field, we developed a new tracking system, which is aiming to overcome the constraints of line-of-sight and paired-point interference in surgical environment. The primary contribution of this study is that the LOS and point correspondence problems can be mitigated using the initial measurements of EMT, and in turn the OPT result can provide initial value for non-linear iterative solver of EMT sensing module.

We developed an integrated optical and electromagnetic tracker comprised of custom multiple infrared cameras, optical marker, field generator and sensing coils, because the current commercial optical or magnetic tracker typically consists of unchangeable lower level proprietary hardware and firmware. For the instrument-affixed markers, the relative pose between passive optical markers and magnetic coils is calibrated. The pose of magnetic sensing coils calculated by electromagnetic sensing module, can speed up the extraction of fiducial points and the point correspondences due to the reduced search space. Moreover, the magnetic tracking can compensate the missing information when the optical markers are temporarily occluded. For magnetic sensing subsystem comprised of 3-axis transmitters and 3-axis receiving coils, the objective function for nonlinear pose estimator is given by the summation of the square difference between the measured sensing data and theoretical data from the dipole model. Non-linear optimisation is computational intensive and requires initial pose estimation value. Traditionally, the initial value is calculated by equation-based algorithm, which is sensitive to noise. Instead, we get the initial value from the measurement of optical tracking subsystem. The real-time integrated tracking system was validated to have tracking errors about 0.87mm. The proposed interactive and tightly coupled sensor-fusion of magnetic-optical tracking method is efficient and applicable for both general surgeries as well as intracorporeal surgeries.


H. Ren K. Wu X. Kang

Despite of the significance of computed tomography (CT) images in surgery planning and guidance, CT scans are not always applicable due to high radiation exposure, particularly risky for children and youth. It is critical to reduce radiation exposure for high sensitive candidates and statistical atlas based approach has therefore been an alternative with minimal radiation exposure.

We addressed the aforementioned challenges through statistical atlas constructions, 3D atlas to 2D radiography registration to get patient-specific models with minimal radiations and multiple-objective optimisation for planning the treatments. Statistical atlas can be employed to construct the global reference map. The atlas then can be registered to a pair of intra-operative fluoroscopy images for constructing a patient-specific model. In this way, we can reduce the radiation exposure to the patients significantly. To characterise shape variations, a statistical shape atlas is constructed using Point Distribution Model, by which a mean shape, modes of shape variation and shape variation are obtained. To construct the patient specific model from the statistical atlas, 3D-2D registration is essential and a back-projected ray based 3D-2D Iterative Closest Point registration method is investigated. Then the treatment planning module for optimal insertion is investigated to avoid critical zone and unnecessary punctures.

The experiment shows the feasibility of the proposed method for atlas-based, image-guided orthopaedic interventions using minimal radiograph and optimal planning. The proposed framework can be extended to other potential applications and one example is for periacetabular osteotomy, particularly for young females which is of great importance to minimise radiation dose during surgical planning and navigation.


D. Breton J. Leboucher V. Burdin O. Rémy-Néris

Introduction

The anterior cruciate ligament (ACL) is one of the most common ligament injuries. Several ACL reconstructions exist and are consequently performed. An accurate and comprehensive description of knee motion is essential for an adequate assessment of these surgeries, in terms of restoring knee motion.

Methods

We propose to compare these reconstructions thanks to an index of articular coherence. This index measures the instantaneous state surface configurations during a motion. More specifically, this refers to the position between two articular surfaces facing each other. First of all, the index has to refer to a position known to be physiological. This initial position of the bones, named reference, directly results from the segmentation of CT scans. First we compute all distances between the two surfaces and then we compute the Cumulative Distribution Function (CDF). We process this way for each iteration of the motion. Then we obtain a batch of CDF curves which provide us qualitative information relative to the motion such as potential collisions or dislocations. The graph of all CDF curves is called Figure of Articular Coherence (FoAC). A good articular coherence is characterised by CDF which are close to the reference. This qualitative method is coupled to a quantitative one named Index of Articular Coherence (IoAC) which computes the Haussdorff distance between the temporal distributions and the reference. This distance has to be as low as possible. The tools were tested on cadaveric experiments of ACL reconstruction provided by Hagemeister et al, (1999). They recorded the knee flexion/extension motion in following situations: the intact knee, after ACL resection, after three methods of ACL reconstruction on the same knee (‘over-the-top’ method (OTT), two different two tunnel reconstructions (2 tunnel). Our method was used, for the time being, for one specimen. We compare different post-surgery kinematics thanks to the FoAC and IoAC.


L.L. Buchan I. Hacihaliloglu R.E. Ellis M.K. Gilbart D.R. Wilson

Introduction

Bony deformities in the hip that cause femoroacetabular impingement (FAI) can be resected in order to delay the onset of osteoarthritis and improve hip range of motion. However, achieving accurate osteoplasty arthroscopically is challenging because the narrow hip joint capsule limits field of view. Recently, image-based navigation using a preoperative plan has been shown to improve the accuracy of femoral bone surfaces following arthroscopic osteoplasty for FAI. The current standard for intraoperative monitoring, 3D x-ray fluoroscopy, is accurate at the initial registration step to within 0.8±0.5mm but involves radiation. Intraoperative 3D ultrasound (US) is a promising radiation-free alternative for providing real-time visual feedback during FAI osteoplasty. The objective was to determine if intraoperative 3D US of the femoral head/neck region can be registered to a CT-based preoperative plan with comparable accuracy to fluoroscopic navigation in order to visualise progress during arthroscopic FAI osteoplasty.

Methods

The experiment used a plastic femur model that had a cam deformity on the femoral head/neck. Thirty metal fiducial markers were placed on the US-accessible anterior and lateral surfaces of the femur. A CT image was acquired and reconstructed, then used to develop a preoperative plan for resection of the cam deformity. Twenty-two sets of 3D US data were then gathered from the phantom using a clinical ultrasound machine and 3D transducer while the phantom was submerged in water. US surfaces from the anterior/lateral regions of the femur were extracted using a recently proposed image processing algorithm. Fiducials in the US volume were manually registered to corresponding CT fiducials to provide a reference standard registration. The reference standard fiducial registration error (FRE) was measured as the average distance between corresponding fiducials. After fiducial-based registration, each US surface was randomly misaligned and re-registered using a coherent point-drift algorithm. The resulting surface registration error (SRE) was measured using average distance between US and CT surfaces. Finally, a plastic model of the preoperative cam deformity resection plan was 3D-printed to represent the postoperative femur. Five US scans were acquired of the postoperative model near the femoral head/neck. Each US scan was initialised for 20 trials using three reference points, and then registered using coherent point drift. Surgical outcome accuracy was reported using final surface registration error (fSRE).


Y. Suksathien R. Suksathien P. Chaiwirattana

Background

The accuracy of cup placement in navigated THA depends on the bony landmark registration intraoperatively. The usual patient position for registration is supine, but supine position has some drawbacks such as it's more difficult for femoral canal visualisation. The alternate patient position is lateral decubitus, but registration in this position may be unreliable because of the contralateral ASIS can't be palpated accurately. The other technique is registration in supine position first and then placing the patient in lateral decubitus for operation. The drawbacks of this technique are time consumption and increased risk of contamination. We created a semilateral decubitus position which combined the advantage of supine position for registration and lateral decubitus position for better femoral canal visualisation. We modified the registration technique by compressing the soft tissue above Pubic Symphysis(PS) to the abdomen and registered at the Antero-Superior-Pubic-Symphysis(ASPS).

Objective

Evaluate the accuracy of cup placement within the “safe zone” and the accuracy of imageless navigation measurement by comparing the intraoperative values of acetabular cup abduction and anteversion to postoperative computed tomography (CT) values.


Junqiang Wang Lei Hu Chunpeng Zhao Yonggang Su Tianmiao Wang Manyi Wang

Objectives

Percutaneous iliosacral screw placement is a standard, stabilization technique for pelvic fractures. The purpose of this study was to assess the effectiveness of a novel biplanar robot navigation aiming system for percutaneous iliosacral screw placement in a human cadaver model.

Methods

A novel biplanar robot navigation aiming system was used in 16 intact human cadaveric pelvises for percutaneous iliosacral screw insertion. The number of successful screw placements and mean time for this insertion and intra-operative fluoroscopy per screw-pair were recorded respectively to evaluate the procedure. The accuracy of the aiming process was evaluated by computed tomography.


B.L. Penenberg M.E. Riley A. Woehnl

Over the last few years low dose digital radiography (DR) has all but replaced traditional chemical image processing. This appears to have created a paradigm shift in the suitability of intraoperative radiographic guidance for total hip arthroplasty. It is the purpose of this publication to describe our preferred technique and assess its reliability in achieving the desired parameters of a successful total hip arthroplasty.

A consecutive prospective evaluation of 150 primary total hip arthroplasties employing intraoperative digital radiography was carried out. An anteroposterior pelvic radiograph with the patient in the lateral decubitus position was obtained for all hips. The orientation of the intraoperative film was matched to that of the preoperative pelvic radiograph. The image was taken after placement of the acetabular component and best estimate of femoral trial size, position, and head and neck length. The DR system produced an image within 6 seconds of exposure. This trial radiograph was then used to make adjustments. Given that the cassette does not have to be moved for image processing, a precise anteroposterior film was obtained by simply adjusting the operating table. Two to three minutes were allotted for each radiograph. Corrections to stem size, cup position, screw length and position, limb length, and offset were made based on this intraoperative radiograph. The final intraoperative image was then compared to a postoperative standard radiograph in supine position at 2 weeks after total hip arthroplasty to verify the accuracy of intraoperative digital radiography. Abduction angle, limb length, offset, and canal fit and fill were assessed for confirmation of the validity of the intraoperative imaging technique.

Acetabular abduction angle was determined with a mean of 43 degrees (range, 35 to 48 degrees). The intraoperative measurement was within 3 degrees of the postoperative measurement in all cases. Adjustment of acetabular cup orientation was performed 10% of the time based on the intraoperative radiograph. Apposition was within 2 mm 100% of the time. Re-seating of the cup was carried out in one hip only. Femoral component was neutral in 92% and between 3 and 5 degrees of varus in 8%. Femoral component was upsized 55% of the time. Intraoperatively measured limb length discrepancy and offset were within 3 mm of the postoperative measurement in all hips.

Intraoperative digital imaging is a reliable tool for achieving the desired radiographic results in THA. The technique is efficient and affordable. The high rate of success in this series suggests that this technology should contribute to a paradigm shift in the standard of care in total hip arthroplasty.


X. Niu Q. Zhang F. Yu T. Wang H. Zhao L. Xu

Background

Resection of sacral chordoma remains challenging because complex anatomy and important nerves in the sacrum make it difficult to achieve wide surgical margins. Computer-assisted navigation has shown promise in aiding in optimal preoperative planning and in providing accurate and precise tumour resection during surgery.

Purpose

To evaluate the benefit of using computer-assisted navigation in precise resection of sacral chordoma.


R. Suksathien Y. Suksathien

Background

Navigated THA is a new procedure in Thailand that has been performed since 2012. The previous studies have reported that navigated THA was a safe, reliable procedure that resulted in a more consistent cup placement compared to the conventional free hand technique and decreased complications of THA, especially dislocation. Perioperative protocols are based on the surgeon's concern about stability of the prosthesis and the patient's health condition. Assuming that the navigator can improve the alignment and stability of THA, the time to start rehabilitation and the post operative length of stay should be reduced in the hospital that does not implement any perioperative protocols. The purpose of this study was to compare the time to start rehabilitation and the length of stay between navigated and non-navigated THA.

Methods

This retrospective study of patients underwent THA using short stem by a single surgeon from March 2011 to November 2012. Seventy-six patients were classified into navigated and non-navigated groups. The patient's characteristic data that were recorded included age, sex, BMI, comorbid illness, diagnosis, ASA classification, preoperative hematocrit, operative time, type of anaesthesia, intraoperative blood transfusion, postoperative length of stay, postoperative complication and time to start rehabilitation. The data were compared between two groups by t-test and chi square test.


C.E. Ponder C. Plaskos E.J. Cheal

Introduction

Intimate bone-implant contact is a requirement for achieving stable component fixation and osseo-integration of porous-coated implants in TKA. However, consistently attaining a press-fit and a tight-fitting femoral component can be problematic when using conventional instrumentation. We present a new robotic cutting-guide system that permits intra-operative adjustment of the femoral resections such that a specified amount of press-fit can be consistently attained.

System Description: A.R.T. (Apex Robotic Technology) employs a miniature bone-mounted robotic cutting-guide and flexible software that permits the surgeon to adjust the anterior and posterior femoral resections in increments of 0.25 mm per resection, allowing a maximum of 1.5mm of total added press in the AP dimension.

Methods

The accuracy of guide-positioning and bone-cutting with A.R.T. was assessed in bench testing on synthetic bones (SAWBONES®) using an optical comparator. The individual guide locations for 16 femoral cut positioning sequences (80 guide positions in total) were measured. Femoral resections were performed with A.R.T. on eight sawbones (two per fit-adjustment setting) and the anterior-posterior dimensions of the final cut surfaces were also measured. Eight sawbones were prepared using conventional instrumentation (jigs) as controls: four with a 0 mm press-fit block and four with a +0.5 mm specially manufactured press-fit block.


J.A. Koenig C. Plaskos

Introduction

We evaluated the utility of imageless computer-navigation coupled with a miniature robotic-cutting guide for managing large deformities in TKA. We asked what effect did severe pre-operative deformities have on post-operative alignment and surgery time using the system. We also report on the early functional outcomes of this group of patients.

Methods

This was a retrospective cohort study of 128 TKA's performed by a single surgeon (mean age: 71y/o [range 53–93], BMI: 31.1 [20–44.3], 48males). Patients were stratified into three groups according to their pre-operative coronal plane deformity: Neutral or mild deformity <10((baseline group); Severe varus ≥10(; severe valgus ≥10(; and according to the degree of flexion contracture: Neutral or mild flexion from −5(hyperextension to 10(flexion (baseline group); hyperextension ≤−5(, and severe flexion ≥10. (The degree of deformity and final postoperative alignment achieved was measured using computer navigation in all patients and analysed using multivariate regression. The APEX CR/Ultra Knee System (OMNIlife Science, Inc.) was used with the PRAXIM Navigation system in all cases. A students t-test was used to compare pre- and post-operative (3–6 months) Knee Society Scores (KSS) and Knee Functional Scores (KSSF) for all patients.


G. Klingenstein M.B. Cross C. Plaskos A.X. Li D. Nam S. Lyman A. D. Pearle D.J. Mayman

Introduction

The aim of this study was to quantify mid-flexion laxity in a total knee arthroplasty with an elevated joint line, as compared to a native knee and a TKA with joint line maintained. Our hypothesis was joint line elevation of 4mm would increase coronal plane laxity throughout mid-flexion in a pattern distinct from the preoperative knee or in a TKA with native joint line.

Methods

Six fresh-frozen cadaver legs from hip-to-toe underwent TKA with a posterior stabilised implant (APEX PS, OMNIlife Science, Inc.) using a computer navigation system equipped with a robotic cutting-guide, in this controlled laboratory cadaveric study. After the initial tibial and femoral resections were performed, the flexion and extension gaps were balanced using navigation, and a 4mm recut was made in the distal femur. The remaining femoral cuts were made, the femoral component was downsized by resecting an additional 4mm of bone off the posterior condyles, and the polyethylene was increased by 4mm to create a situation of a well-balanced knee with an elevated joint line. The navigation system was used to measure overall coronal plane laxity by measuring the mechanical alignment angle at maximum extension, 30, 45, 60 and 90(of flexion, when applying a standardised varus/valgus load of 9.8Nm across the knee using a 4kg spring-load located at 25cm distal to the knee joint line. Laxity was also measured in the native knee, as well as the native knee after a standard approach during TKA which included a medial release. Coronal plane laxity was defined as the absolute difference (in degrees) between the mean mechanical alignment angle obtained from applying a standardised varus and valgus stress at 0, 30, 45, 60 and 90(.


J.Y. Jenny A. Viau

Introduction

Leg length discrepancy is a significant concern after total hip replacement (THR). We hypothesised that the intra-operative use of a navigation system was able to accurately control the leg length during THR.

Material

50 cases have been prospectively analysed. There were 29 men and 21 women, with a mean age of 66.1 years (range, 50 to 80 years), all operated on for THR for end-stage hip osteoarthritis.


J.Y. Jenny

Introduction

An optimal reconstruction of the joint anatomy and physiology during revision total knee replacement (RTKR) is technically demanding. A new software was developed to allow a virtual planning of the joint reconstruction just after removal of the primary prosthesis.

Material

Following changes have been implemented to the standard navigation software: 1) to define and control the vertical level of the joint space on both tibia and femoral side, and to allow performing the potential change decided prior to the revision procedure according to the preoperative imaging planning; 2) to measure the tibio-femoral gaps independently in flexion et en extension on both medial and lateral tibio-femoral joints; 3) to virtually plan and control the vertical level and the orientation of the tibia component; 4) to virtually plan and control the sizing and the 3D positioning of the femoral component; 5) to virtually plan and control the potential bone resection; 6) to virtually plan and control the potential bone defects and their reconstruction (bone graft or augments); 7) to virtually plan and control the size, the length and the orientation of the stems extensions independently on the femoral and on the tibia side.


S.S. Hung P.L. Yen M.Y. Lee G.F. Tseng

To develop a useful surgical navigation system, accurate determination of bone coordinates and thorough understanding of the knee kinematics are important. In this study, we have verified our algorithm for determination of bone coordinates in a cadaver study using skeletal markers, and at the same time, we also attempted to obtain a better understanding of the knee kinematics.

The research was performed at the Medical Simulation Center of Tzu Chi University. Optical measurement system (Polaris® Vicra®, Northern Digital Inc.) was used, and reflective skeletal markers were placed over the iliac crest, femur shaft, and tibia shaft of the same limb. Two methods were used to determine the hip center; one is by circumduction of the femur, assuming it pivoted at the hip center. The other method was to partially expose the head of femur through anterior hip arthrotomy, and to calculate the centre of head from the surface coordinates obtained with a probe. The coordinate system of femur was established by direct probing the bony landmarks of distal femur through arthrotomy of knee joint, including the medial and lateral epicondyle, and the Whiteside line. The tibial axis was determined by the centre of tibia plateau localised via direct probing, and the centre of ankle joint calculated by the midpoint between bilateral malleoli. Repeated passive flexion and extension of knee joint was performed, and the mechanical axis as well as the rotation axis were calculated during knee motion.

A very small amount of motion was detected from the iliac crest, and all the data were adjusted at first. There was a discrepancy of about 16.7mm between the two methods in finding the hip centre, and the position found by the first method was located more proximally. When comparing the epicondylar axis to the rotation axis of the tibia around knee joint, there was a difference of 2.46 degrees. The total range of motion for the knee joint measured in this study was 0∼144 degrees. The mechanical axis was found changing in an exponential pattern from 0 degrees to undetermined at 90 degrees of flexion, and then returned to zero again. Taking the value of 5 degrees as an acceptable range of error, the calculated mechanical axis exceeded this value when knee flexion angle was between 60∼120 degrees.

The discrepancy between the hip centres calculated from the two methods suggested that the pivoting point of the femur head during hip motion might not be at the center of femur head, and the former location seemed closer to the surface of head at the weight bearing site. Under such circumstances, the mechanical axis obtained through circumduction of the thigh might be 1∼2 degrees different from that obtained through the actual center of femur head. During knee flexion, the mechanical axis also changed gradually, and this could be due to laxity of knee joint, or due to intrinsic valgus/varus alignment. However, the value became unreliable when the knee was at a flexion angle of 60∼120 degrees, and this should be taken into account during navigation surgery.


V. Hofbauer T. Bittrich J. Glasbrenner C. Koesters M. Raschke

INTRODUCTION

The medial patellofemoral ligament (MPFL) has been recognised as the most important medial structure preventing lateral dislocation or subluxation of the patella (LeGrand 2007). After MPFL rupture the patella deviates from the optimal path resulting in an altered retropatellar pressure distribution. This may lead to an early degeneration with loss of function and need for endoprosthetic joint replacement. The goal of this study was to obtain first data about retropatellar pressure distribution under simulation of physiological quadriceps muscle loading and evaluate the influence of ligament instabilities.

MATERIALS AND METHOD

On ten fresh-frozen cadaveric knees the quadriceps muscle was divided into 5 parts along their anatomic fiber orientation analogous to Farahmand 1998. Muscular loading was achieved by applying weights to each of the five components in proportion to the cross sectional muscle area (total load 175 N).

A custom made sensor was introduced between the patella and femur [Pliance, Novel / Germany]. The sensor consists of 85 single cells. The robot-control-unit is liked to a force-torque sensor. The force free knee-flexion-path from 0° to 90° was calculated during three “passive path” measurements. The actual measurements followed with identical parameters.

At first, the retropatellar pressure distribution was recorded with intact ligaments (“native”). After cutting the MPFL the test was repeated. Then double bundle MPFL reconstruction (Schoettle 2009) was performed and the pressure distribution was obtained again. Minimum, mean and maximum pressures and forces were statistically compared in each of the three tested conditions (native Patella with intact MPFL, cut and reconstructed MPFL). We followed the hypothesis that MPFL reconstruction can restore native retropatellar pressure distribution.


J.R. Smith F. Picard P.J. Rowe A. Deakin P.E. Riches

Unicondylar knee arthroplasty (UKA) is a treatment for osteoarthritis when the disease only affects one compartment of the knee joint. The popularity in UKA grew in the 1980s but due to high revision rates the usage decreased. A high incidence of implant malalignment has been reported when using manual instrumentation. Recent developments include surgical robotics systems with navigation which have the potential to improve the accuracy and precision of UKA.

UKA was carried out using an imageless navigation system – the Navio Precision Freehand Sculpting system (Blue Belt Technologies, Pittsburgh, USA) with a medical Uni Knee Tornier implant (Tornier, Montbonnot Saint Martin, France) on nine fresh frozen cadaveric lower limbs (8 males, 1 females, mean age 71.7 (SD 13.3)). Two users (consultant orthopaedic surgeon and post doctoral research associate) who had been trained on the system prior to the cadaveric study carried out 4 and 5 implants respectively. The aim of this study was to quantify the differences between the planned and achieved cuts.

A 3D image of the ‘actual’ implant position was overlaid on the planned implant image. The errors between the ‘actual’ and the planned implant placement were calculated in three planes and the three rotations. The maximum femoral implant rotational error was 3.7° with a maximum RMS angular error of 2°. The maximum femoral implant translational error was 2.6mm and the RMS translational error across all directions was up to 1.1mm. The maximum tibial implant rotational error was 4.1° with a maximum RMS angular error was 2.6°. The maximum translational error was 2.7mm and the RMS translational error across all directions was up to 2.0mm.

The results were comparable to those reported by other robotic assistive devices on the market for UKA. This technology still needs clinical assessment to confirm these promising results.


J.R. Smith M. Blyth B. Jones A. MacLean P.J. Rowe

Total knee arthroplasty (TKA) has been established as a successful procedure for relieving pain and improving function in patients suffering from severe knee osteoarthritis for several decades now. It involves removing bone from both the medial and lateral compartments of the knee and sacrificing one or both of the cruciate ligaments. This in turn is likely to have an impact on the patients' functional outcome. In subjects where only one compartment of the knee joint is affected with osteoarthritis then unicondylar knee arthroplasty (UKA) has been proposed as an alternative procedure to TKA. This operation preserves the cruciate ligaments and removes bone only from the affected side of the joint. As a result there is the possibility of an improved functional outcome post surgery. UKA has been associated with faster recovery, good functional outcome in terms of range of motion and it is bone sparing compared to TKA. However, the biggest obstacle to UKA success is the high failure rates.

The aim of this study was to compare the functional outcome of computer navigated TKA (n=60) and UKA (n=42) patients 12 month post operation using flexible electrogoniometry. Flexible electrogoniometry was used to investigate knee joint kinematics during gait, slopes walking, stair negotiation, and when using standard and low chairs. Maximum, minimum and excursion knee joint angles were calculated for each task.

The biomechanical assessment showed statistically significant improvements in the knee kinematics in terms of maximum (p<0.0004) and excursion (p<0.026) knee joint angles in the UKA patient group compared to the navigated TKA group for each of the functional tasks. There was no statistically significant difference between the minimum knee joint angles during these functional tasks (p>0.05).

Therefore, UKA patients were showed to have a significantly better functional outcome in terms of the maximum knee joint angle during daily tasks. A limitation of this study is that it compares two cohorts rather than two randomised groups. It is expected that UKA patients will have a better functional outcome. Our results suggest that for patients with less severe knee osteoarthritis, UKA may offer a better functional outcome than the more common surgical option of TKA. The recent advancements in computer assisted and robotic assisted knee arthroplasty has the possibility to improve the accuracy of UKA and therefore led to the increase in confidence and in usage in a procedure which has the potential to give patients a superior functional outcome.


G. Alhares J. Eschweiler K. Radermacher

Knee biomechanics after total knee arthroplasty (TKA) has received more attention in recent years. One critical biomechanical aspect involved in the workflow of present TKA strategies is the intraoperative optimisation of ligament balancing. Ligament balancing is usually performed with passive flexion-extension in unloaded situations. Medial and lateral ligaments strains after TKA differ in loaded flexion compared to unloaded passive flexion making the passive unloaded ligament balancing for TKA questionable. To address this problem, the development of detailed and specific knowledge on the biomechanical behaviour of loaded knee structures is essential. Stress MRI techniques were introduced in previous studies to evaluate loaded joint kinematics. Previous studies captured the knee movement either in atypical loading supine positions, or in upright positions with help of inclined supporting backrests being insufficient for movement capture under full body weight-bearing conditions.

In this work, we proposed a combined MR imaging approach for measurement and assessment of knee kinematics under full body weight-bearing in single legged stance as a first step towards the understanding of complex biomechanical aspects of bony structures and soft tissue envelope. The proposed method is based on registration of high resolution static MRI data (supine acquisition) with low resolution data, quasi-static upright-MRI data (loaded flexion positions) and was applied for the measurement of tibio-femoral kinematics in 10 healthy volunteers. The high resolution MRI data were acquired using a 1.5T Philips-Intera system, while the quasi-static MRI data (full bodyweight-bearing) was obtained with a 0.6T Fonar-Upright™ system. Contours of femur, tibia, and patella from both MRI techniques were extracted using expert manual segmentation. Anatomical surface models were then obtained for the high resolution static data.

The upright-MRI acquisition consisted of Multi-2D, quasi-static sagittal scans each including 4 slices for each flexion angle. Starting with full knee extension, the subjects were asked to increase the flexion in 4–5 steps to reach the maximum flexion angle possible under space and force limitations. Knees were softly padded for stabilisation in lateral-medial direction only in order to reduce motion artifacts. During the upright acquisition the subjects were asked to transfer their bodyweight onto the leg being imaged and maintain the predefined flexion position in single legged stance. The acquisition at every flexion angle was obtained near the scanner's isocenter and takes ∼39 seconds.

The anatomical surface models of the static data were each registered to their corresponding contours from the weight-bearing scans using an iterative closest point (ICP) based approach. A reference registration step was carried out to register the surface models to the full extension loaded position. The registered surfaces from this step were then considered as initial conditions for next ICP registration step. This procedure was similarly repeated to ensure successful registrations between subsequent flexion acquisitions.

The tibio-femoral kinematics was calculated using the joint coordinate system (JCS). The combined MR imaging approach allows the non-invasive measurement of kinematics in single legged stance and under physiological full weight-bearing conditions. We believe that this method can provide valuable insights for TKA for the validation of patient-specific biomechanical models.


P.S. Young S.W. Bell A. Mahendra

The surgical management of musculoskeletal tumours is a challenging problem, particularly in pelvic and diaphyseal tumour resection where accurate determination of bony transection points is extremely important to optimise oncologic, functional and reconstructive options. The use of computer assisted navigation in these cases could improve surgical precision.

We resected musculoskeletal tumours in fifteen patients using commercially available computer navigation software (Orthomap 3D). Of the eight pelvic tumours, three underwent biological reconstruction with extra corporeal irradiation; three endoprosthetic replacement (EPR) and two required no bony reconstruction. Four diaphyseal tumours had biological reconstruction. Two patients with proximal femoral sarcoma underwent extra-articular resection and EPR. One soft tissue sarcoma of the adductor compartment involving the femur was resected with EPR.

Histological examination of the resected specimens revealed tumour free margins in all cases. Post-operative radiographs and CT show resection and reconstruction as planned in all cases. Several learning points were identified related to juvenile bony anatomy and intra-operative registration.

The use of computer navigation in musculoskeletal oncology allows integration of local anatomy and tumour extent to identify resection margins accurately. Furthermore, it can aid in reconstruction following tumour resection. Our experience thus far has been encouraging.


H. Lin J.Q. Wang

Objectives

Femoral shaft fracture treatment often results in mal-alignment and the high dosage of radiation exposure. The objective of this study is to develop a Parallel Manipulator Robot (PMR) on traction table to overcome these difficulties so as achieve better alignment for the fractured femur and reduce radiation to both patients and physicians.

Methods

The distal platform of PMR is attached to the central pole on standard traction table by the boot adaptor. A leg model with soft tissue made by Pacific Research Laboratory, Inc. is flexed at the knee with patella on the top. A 2/3 circular ring, with 1/3 open circle down, fixed to the fractured distal femur with one trans-wire and one self-tapping screw, acting as adaptable stirrup fixing scheme. To secure proximal femur, an adapter is assembled on the traction table and fixed on the proximal femur. The distal femur is fixed to the 2/3 circular ring platform of PMR. Surgical planning is performed by first acquiring the bi-planar images from the C-Arm X-ray machine. After simulated fracture on 3-D femoral model is made, proximal and distal segments of the model will be superimposed with background bi-planar images. Finally the pre-fractured length and mechanical axis of 3-D femoral model will be restored. Afterwards, a table of schedule for length adjustments of six struts of PMR is generated. This length adjustment schedule is used to drive the PMR for fractured femur alignment and reduction. When reduction completed, a special designed device is used to fix the reduced femur. Then the PMR is removed from the traction table and the patient can be removed from the traction table.


A. Jaramaz C. Nikou A. Simone

NavioPFS™ is a hand-held robotic technology for bone shaping that employs computer control of a high-speed bone drill. There are two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. The unicondylar knee replacement (UKR) application uses the image-free approach in which a mix of direct and kinematic referencing is used to define all parameters relevant for planning. After the bone cutting plan is generated, the user freely moves the NavioPFS handpiece over the bone surface, and carves out the parts of the bone targeted for removal. The real-time control loop controls the depth or speed of cut, thus resulting in the planned bone preparation. This experiment evaluates the accuracy of bone preparation and implant placement on cadaveric knees in a simulated clinical setting.

Three operators performed medial UKR on two cadaver specimens (4 knees) using a proprietary implant design that takes advantage of the NavioPFS approach. In order to measure the placement of components, each component included a set of 8 conical divots in predetermined locations. To establish a shared reference frame, a set of four fiducial screws is inserted in each bone. All bones were cut using a 5 mm spherical bur. Exposure Control was the primary mode of operation for both condylar cuts – although the users utilised Speed Control to perform some of the more posterior burring activities and to prepare the peg holes. Postoperatively, positions of conical divots on the femoral and tibial implants and on the respective four fiducial screws were measured using a Microscribe digitising arm in order to compare the final and the planned implant position.

All implants were placed within 1.5 mm of target position in any particular direction. Maximum translation error was 1.31 mm. Maximum rotational error was 1.90 degrees on a femoral and 3.26 degrees on a tibial component. RMS error over all components was 0.69mm/1.23 degrees.

This is the first report of the performance of the NavioPFS system under clinical conditions. Although preliminary, the results are overall in accordance with previous sawbones studies and with the reports from comparable semi-active robotic systems that use real time control loop to control the cutting performance.

The use of NavioPFS in UKR eliminates the need for conventional instrumentation and allows access to the bone through a reduced incision. By leveraging the surgeon's skill in manipulating soft tissues and actively optimising the tool's access to the bone, combined with the precision and reproducibility of the robotic control of bone cutting, we expect to make UKR surgery available to a wider patient population with isolated medial osteoarthritis that might otherwise receive a total knee replacement. In addition to accurate bone shaping with a handheld robotically controlled tool, NavioPFS system for UKR incorporates a CT-free planning system. This approach combines the practical advantages of not requiring pre-operative medical images, while still accurately gathering all key information, both geometric and kinematic, necessary for UKR planning.


B. Jaramaz F. Picard A. Gregori

NavioPFS™ unicondylar knee replacement (UKR) system combines CT-free planning and navigation with robotically assisted bone preparation. In the planning procedure, all relevant anatomic information is collected under navigation, either directly with the point probe or by kinematic manipulation. In addition to key anatomic landmarks and the maps of the articulating surfaces of the femur and tibia, kinematic assessment of the joint laxity is performed. Relative positions of femur and tibia are collected through the flexion/extension range, with the pressure applied to fully stretch the collateral ligament on the operative side.

The planning procedure involves three stages: (1) the implant sizing and initial placement,(2) balancing of the gap on the operative side and (3) evaluating the contact points for the recorded flexion data and the planned placement of implants. In the gap balancing stage, the implants are repositioned until they allow for a positive gap, preferably uniform, throughout the entire range of flexion. UKR was planned and prepared on six cadaver knees with the help of NavioPFS system. All knees were normal without any signs of osteoarthritis. Two surgeons have performed medial UKR (4+2), and the bones were prepared using the NavioPFS handheld robotic tool.

Postoperatively, we have re-used the data collected during the planning procedure to compare the kinematic (gap balancing) performance of the used implant with three different commercial implant designs. All implants were placed in the orientation recommended by the respective manufacturer, sized to best fit the original bone geometry, and repositioned optimally balance the gap curve through the entire flexion range, without any negative gaps (overlaps). Since these were nonarthritic cadaver knees, the intent was to restore the original preoperative varus/valgus in neutral (zero) flexion.

The three implant designs demonstrated variable degree of capability to uniformly balance the knee gap over the entire range of flexion. The first implant (A) required a gap larger than 2 mm in one case out of six, the second (B) was capable of producing the positive gap curve under 2mm of gap in all six cases, and the third (C) required a gap larger than 2 mm in 3 (50%) of cases. All three designs exhibit the reduced gap space in mid (30°–90°) flexion.

Despite the best attempts, the artificial implants do not fully replicate the healthy knee kinematics. This is manifested by increased tightness in the mid flexion. In order to balance the gap in mid flexion, additional laxity has to be allowed in full flexion, extension, or both. NavioPFS allows for patient specific planning that takes into account this information, only available intraoperatively. This kind of evaluation on a patient specific basis is a very important planning tool and it allows the insight on the implant performance in mid flexion, typically not available using conventional planning techniques. It can also help in improving kinematic performance of future implant designs.


A. Marquez-Lara D. Curtis R.M. Patel S.D. Stulberg

Femoral components used in total hip arthroplasty (THA) rely on good initial fixation determined by implant design, femoral morphology, and surgical technique. A higher rate of varus alignment may be of specific concern with short stem implants. Varus placement in uncemented femoral components has been proven not to be detrimental to clinical function; though long-term bone remodeling secondary to varus placement remains unknown. The goal of this study was to compare the clinical and radiographic outcomes in patients who underwent THA with one of two uncemented short stem metaphyseal engaging implants at minimum two-year follow-up.

A review of 105 patients (average age 65 years; BMI 29 kg/m2) who underwent a total of 109 primary THAs using the ABG II short stem femoral implant (Stryker, Mahwah, NJ), and 160 hips in 149 patients (average age 70 years; BMI 28 kg/m2) who underwent primary THA using the Citation stem (Stryker, Mahwah, NJ). The same surgeon (SDS) performed all surgeries through a less invasive posterolateral approach. Pre-operative and post-operative Harris Hips Scores (HHS) and WOMAC scores were collected. Digital radiograph analysis was performed including measuring the stem alignment relative to the femoral shaft. A stem placed with greater than 5 degrees of varus was considered to be in varus.

There was no significant difference in demographics (age, gender or BMI) or pre-operative HHS and WOMAC scores between the two groups. Follow-up HHS was 90 (range 63–100) and 94 (range 70–100) for the ABG II and Citation groups, respectively. Follow-up WOMAC scores were 10 (range 0–24) and 6 (range 0–43) for the ABG II and Citation groups, respectively. There was no statistically significant difference in any of the scores between the two groups (p>0.05).

When looking at AP radiographs for postoperative intramedullary alignment, none of the ABG II implants were placed in varus (>5°), while a small number (4.9%) of Citation implants were implanted in varus alignment. No significant difference was observed in the alignment between the two groups (p>0.05). Average post-op alignment with the ABG was 1.10° (range −4.7–4.9°) and 0.88° (range −4.5–8.9°) with the Citation.

The clinical results associated with the use of these stems in patients of all ages and bone types have been identical to those achieved by uncemented stems of standard length. Both implants in this study had excellent clinical and functional results in primary THA after a minimum 24-month follow up. In addition, postoperative radiographic analysis demonstrated that these stems can be reliably and reproducibly placed in neutral alignment despite their short length. The lateral flare on the Citation implant led to a greater number of implants in varus alignment, potentially affecting offset and leg-length, yet the relative increased incidence compared to the ABG II was not significant. Further research is needed in designing implants that optimize proximal femoral contact while maintaining alignment and overall hip kinematics.


J. Franke S.Y. Vetter I. Mühlhäuser P.A. Grützner J. von Recum

Background

Digital planning of implants in regard to position and size is done preoperatively in most cases. Intraoperative it can only be made by navigation systems. With the development of the VIPS-method (Virtual Implant Planning System) as an application for mobile C-arms, it is possible to do an intraoperative virtual planning of the screws near the joint in treatment of distal radius fractures by plating. Screw misplacement is a well known complication in the operative treatment of these fractures. The aim of this prospective randomised trial was to gain first clinical experiences and to compare VIPS with the conventional technique. The study hypothesis was that there will be less screw misplacement in the VIPS group.

Methods

We included 40 patients with distal radius fractures type A3, C1 and C2 according to the AO-classification. In a pilot study the first 10 Patients were treated by the VIPS method to gain experience with VIPS in a clinical set-up. The results of the pilot-study are not part of this analysis. Then 15 Patients were web-based randomised into two groups. After diaphysial fixation of a 2.4 mm Variable Angle Two-Column Volar Distal Radius Plate and fracture reduction matching of a three-dimensional virtual plate to the two-dimensional image of the plate in the fluoroscopy shots in two plains was performed automatically in the VIPS group. The variable angle locking screws were planed in means of direction and length. Drilling was done by the use of the Universal Variable Angle Locking Drill Guide that was modified by laser marks at the rim of the cone to transfer the virtual planning. The drill guide enables drilling in a cone of 30°. In the control group the same implant was used in a conventional technique that means screw placement by the surgeon without digital planning. After implant placement an intraoperative three-dimensional scan was performed to check the position and length of the screws near the joint. OR- and fluoroscopy-time was documented. In addition the changes of misplaced screws were engaged.


M Changulani A.H. Deakin F. Picard

Distal femur resection for correction of flexion contractures in total knee arthroplasty (TKA) can lead to joint line elevation, abnormal knee kinematics and patellofemoral problems. The aim of this retrospective study was to establish the contribution of soft tissue releases and bony cuts in the change in maximum knee extension in TKA.

Data were available for 209 navigated TKAs performed by a single surgeon using a medial approach. All patients had the same cemented implant, either CR or PS, which both required a minimum thickness of 10 mm for the tibial and 9mm for the femoral component. Intra-operatively pre- and post-implant extension angles and the size of bone resection were collected using a commercial navigation system. The thickness of polyethylene insert and the extent of soft tissue release performed (no release, moderate and extensive release) were collected from the patient record. A univariate linear regression model was used to predict change in maximum extension from pre- to post-implant.

The mean bone resection was 19mm (15 to 28 mm) (Figure 1).79% of polyethylene inserts were 10mm thick (10 to 16 mm). 71% of knees had no soft tissue release. The mean increase in extension was 5° (11° decrease to 23° increase) (Figure 1). The analysis showed that bone cuts (p<0.001), soft tissue release (p=0.001) and insert thickness (p=0.010) were all significant terms in the model (r2adj=0.170). This model predicted that carrying out a TKA with 19mm bone cuts, 10mm insert and no soft tissue release would give 4.2° increase in extension. It predicted that a moderate release would give a 2.8° increase in extension compared to no release, with an extensive release giving 3.9° increase over no release. For each mm increase in bone cuts the model predicted a 0.8° increase in extension and for each mm increase in insert size a decrease extension by 1.1°.

Preoperative FFC contracture is a frequent condition in TKA that the surgeon has to address either by resecting more bone or by extending soft tissue release to increase the extension gap to fit the knee implant. This analysis of 209 navigated knee arthroplasty showed that both options are suitable to increase the extension gap. The modelling results show that in general to increase maximum extension by the same as an extensive soft tissue release that bone cuts would have to be increased by 4–5mm. However this model only accounted for 17% of the variation in change in extension pre- to post-implant so is poor at predicting outcomes for specific patients. The large variation in actual FFC correction indicates that this relies on factors other than bone cuts and soft tissue releases as quantified in this study.


G Picard M Blair F Picard

The amount of time spent in theatre by trainees is decreasing and therefore it seems crucial to fully optimis e these to enable adequate training. Trainees at the beginning of their practice, despite their exposure to surgery, cannot always take advantages of the surgical procedure they are assisting with. An obvious example of this is total hip replacement during posterior approach. Although the posterior approach and less invasive or minimally invasive approaches are certainly beneficial for patients, they are very difficult for a young trainee to comprehend, as they spend most of the time hanging onto the retractor without or rarely seeing the important anatomic steps of the procedure. Our goal was to develop a tool that would help a trainee to fully see and understand the surgical steps of total hip replacement during a posterior approach.

To enable visualisation of the operation from the senior surgeon's perspective we developed a device to film the surgery and output the video feed to a screen. The prototype used an HD Replay XD1080 camera connected to a WDHI Xenta transmitting dongle (transmitting frequency −5.8 GHz), with an onboard 6600 mAh external Li-Mh battery providing 1A of current to the system. The Replay camera was fixed to the surgeon's ventilation helmet, and took its power from the battery supplying both the fan system and the transmitting unit. The surgeon can then clip both of these items to his belt and the connecting wires and cables run up his back. The device provided a Full HD video output of the surgery from the surgeon's perspective. The receiving unit used a Xenta WHDI wireless receiver with HDMI and DVI-I/D connections allowing the video to be displayed on any screen in the operating room with these connections.

The prototype has been trialled by the senior author and was successful in allowing the direct surgeon's view of the procedure to be displayed on a screen in the theatre so that other staff involved in the operation could see it.

Although the use of virtual training, presentations and video are essential to training, surgical training still relies greatly upon surgical assistance. The introduction of an intra-operative video feedback device would enable trainees to observe the operation from a first-person perspective which could lead to a considerable reduction in the amount of training time required, as well as a better understand of the specific surgical steps in a procedure. This would be particularly use for operations where a trainee assists the surgeon from the opposite side of the operating table, for example when undergoing total hip replacement during posterior approach. We can also envision this device also being used by surgeons to monitor their trainees when operating, and perhaps to keep a record of the operations undertaken in an establishment for archiving or assessment.


N.C. Sciberras A.H. Deakin F. Picard

The Columbus® knee system was designed as a standard knee implant that allows high flexion without the need for additional bone resection. The aim of this retrospective study was to investigate the correlation between the maximum flexion achieved at five years and the slope of the tibial component. The hypothesis was that increased slope would give increased flexion.

The study design was a retrospective cohort study at a single centre. The inclusion criterion was having had a navigated cemented Columbus primary TKA implanted between March 2005 and December 2006 using the image free OrthoPilot® navigation system (Aesculap, Tuttlingen, Germany) in our institution. Follow-up had been carried out at review clinics by an independent arthroplasty team. Patient-related data had been recorded either in case notes, the departmental proprietary database or as radiographic images. In addition to demographics, five-year follow-up range of motion (ROM) was collected. All available radiographs on the national Picture Archiving and Communication System (Eastman Kodak Company, 10.1_SP1, 2006), whether taken at our institution or at the patient's local hospital, were analysed by a trainee orthopaedic surgeon (NCS) who was independent of the patients' care. Component position according to the Knee Society TKA scoring system was determined from the five-year review lateral x-ray. The tibial slope was calculated as 90° minus the angle of the tibial component so giving a posterior slope as a positive number and an anterior slope as a negative number. The correlation between maximum flexion angle and tibial slope was calculated. Further to this a subgroup of only CR prostheses and patients with BMI <35 were analysed for a relationship. The tibial slope of the group of patients having 90° or less of flexion (poor flexion) was compared to those having 110° or more (good flexion) using a t-test, as was the flexion of the those with BMI <30 to those with BMI > 35.

A total of 219 knees in 205 patients were identified. 123 had five-year radiograph and maximum flexion measurement available. Cohort demographics were mean age 68(8.6), mean BMI 32.0(5.9) and mean maximum flexion at five years of 101°(11°). The tibial slope angle showed variation around the mean of 2°(2.8°). There was no correlation between tibial slope and maximum flexion for either that whole cohort (r=-0.051, p=0.572, Figure 1b) or the subgroup of CR and BMI <35 patients (n=78, r = −0.089, p=0.438). The mean tibial slope of those patients having poor flexion was 2° (SD2.6°) and this was not significantly different to the mean for those with good flexion, 3° (SD3.1°) p=0.614. The mean flexion of those with BMI <30 was 100° (SD8.7°) and this was not significantly different to those with BMI >35, mean 101° (SD11.4°).

This study did not find any correlation between the tibial slope and maximum flexion angle in 123 TKAs at five year follow up. Further studies with a more accurate measurement of tibial slope should be carried out to confirm whether a relationship exists in the clinical setting.


B. Sankar R. Venkataraman M. Changulani S. Sapare K. Deep F. Picard

In arthritic knees with severe valgus deformity Total Knee Arthroplasty (TKA) can be performed through medial or lateral parapatellar approaches. Many orthopaedic surgeons are apprehensive of using the lateral parapatellar approach due to lack of familiarity and concerns about complications related to soft tissue coverage and vascularity of the patella and the overlying skin. However surgeons who use this approach report good outcomes and no added complications. The purpose of our study was to compare outcomes following TKA performed through a medial parapatellar approach with those performed through a lateral parapatellar approach in arthritic knees with severe valgus deformity.

We conducted a retrospective review of patients from two consultants using computer navigation for all their TKAs. All patients with severe valgus deformities (Ranawat 2 & 3 grades) operated on between January 2005 and December 2011 were included. 66 patients with 67 TKAs fulfilled the inclusion criteria. Patients were group by approach; Medial = 34TKAs (34 patients) or Lateral = 33 TKAs (32 patients). Details were collected from patients' records, AP hip-knee-ankle (HKA) radiographs and computer navigation files. Outcome measures included lateral release rates, post-operative range of knee movements, long leg mechanical alignment measurements, post-operative Oxford scores at six weeks and one year, patient satisfaction and any complications. Comparisons were made between groups using t-tests.

The total cohort had a mean age of 69 years [42–82] and mean BMI of 29 [19–46]. The two groups had comparable pre-operative Oxford scores (Medial 41[27–56], Lateral 44 [31–60]) and pre-operative valgus deformity measured on HKA radiographs (Medial 13° [10°–27.6°], Lateral 12° [6°–22°]). Three patients in the Medial group underwent intra-operative lateral patellar release to improve patellar tracking. Seven patients in the Lateral group had a lateral condyle osteotomy for soft tissue balancing (one bilateral). There was no statistically significant difference between groups at one year follow up for maximum flexion (Medial 100° [78°–122°], Lateral 100° [85°–125°], p=0.42), fixed flexion deformity (Medial 1.2° [0°–10°], Lateral 0.9° [0°–10°], p=0.31) or Oxford score (Medial 23 [12–37], Lateral 23 [16–41], p=0.49). Similarly there was no difference in the patient satisfaction rates between the two groups at one year follow up. However there was a statistically significant difference in the mean radiographic post-operative alignment angle measurement (Medial 1.8° valgus [4° varus to 10° valgus], Lateral 0.3° valgus [5° varus to 7° valgus], p=0.02). One patient in the Medial group had a revision to hinged knee prosthesis for post-operative instability. There was no wound breakdown or patellar avascular necrosis noted in either of the groups.

The lateral parapatellar approach resulted in slightly better valgus correction on radiographs taken six weeks post-operatively. We found no major complications in the Lateral parapatellar approach group. Specifically we did not encounter any difficulties in closing the deep soft tissue envelope around the knee and there were no cases of patellar avascular necrosis or skin necrosis. Hence we conclude that lateral parapatellar approach is a safe and reliable alternative to the medial parapatellar approach for correction of severe valgus deformity in TKA.


M. Bayers-Thering M. J. Phillips K. A. Krackow

Total knee arthroplasty is well documented to be a very successful operation, proper alignment and soft tissue balancing is important. Computer navigation for TKA has been available for more than 10 years. This paper reviews our outcomes and the lessons learned from CAS.

October 1, 2001 we preformed the first clinical case of a navigated TKA in North America. We tracked our early results at with 1 year of follow up of 150 navigated knee cases and compared there data to 50 non- navigated knees. Long standing lower extremity x-rays were measured to determine mechanical alignment. In 2011 we reviewed all cases to date to determine if there were pin site problems. In 2012 we looked at are recurvatum data. Oct 2011 was our 10th year using the computer navigation system for TKA. We reviewed what we have learned and assess our outcome data on patients who were at least 9.5 years post surgery. All patients received long standing lower extremity x-rays pre-operatively and at 10 year follow up. Any problems or revisions were noted. Our early results will be compared to our 10 year results.

Our 1 year results showed no difference in clinical outcome or range of motion compared to the non-navigated group. The navigated knee group had better alignment; 52% were in neutral alignment, vs. 23% in the non-navigated group. Overall the navigated group, 80% of all alignment was within 1.5 degrees of neutral while the non-navigated groups 80 % of cases were between 5° valgus and 4° varus. Our data for 10 year follow up (range 9.5–10.5 years) is the similar to our early results. We have seen 42 patients, 44 knees. The alignment from long standing lower extremity x-rays, 53% were neutral or +/− 1°. Twenty eight knees of 43 were +/− 3°. There were 3 revisions in this small group. One was revised for a loose tibial base plate with osteolysis on the tibia and femur. The revision was 10 years after the index surgery. There were 2 other revisions, both for infection, were treated with a poly exchange and wash out. To date we have done 2030 navigated knee cases and our data shows that 13.9% demonstrate genu recurvatum. The range was 0.5° to 30°, 104 patients, 5.1% had more than 5° recurvatum. In the literature recurvatum rates are reported at about 1%. After reviewing all case to date in we did not observe any pin site problems.

CAS is still the main objective measure we have in the operating room to date. The advantages of CAS are it provides real time assessment of the true varus/valgus deformity, initial extension and medial/lateral soft tissue imbalance and anticipates final trial reduction. We are performing less soft tissue releases most likely because our tibia and femoral cuts are more precise. Our 10 year follow up data while encouraging requires more investigation.


S. Khamaisy B. P. Gladnick D. Nam K. R. Reinhardt A.D. Pearle

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs.


M. de la Fuente S. Jeromin A. Boyer S. Billet S. Lavallée J. Stiehl K. Radermacher

Major aspects on long-term outcome in Total Knee Arthroplasty are the correct alignment of the implant with the mechanical load axis, the rotational alignment of the components as well as good soft tissue balancing. To reduce the variability of implant alignment and at the same time minimise the invasiveness different computer assisted systems have been introduced.

To achieve accuracy as high as those of a robotic system but with a pure mechanically adjustable cutting block, the Exactech GPS system has been developed. The new concept comprises a seamlessly planning and navigation screen with an integrated optical tracking system for fast and accurate acquisition and verification of anatomical landmarks within the sterile field as well as a tiny cutting guide for accurate transfer of the planned bone resections.

Using a conventional screwdriver the cutting block could be accurately aligned with the planned resection by controlling the current position of the cutting block on the navigation screen. To save time, to maximise the ease of use and to minimize the surgeon's mental workload during adjustment, a smart screwdriver (SSD) has been developed being able to automatically adjust the screws.

The basic idea of the smart screwdriver is to have a system providing an automatic transfer of the planned data to the cutting guide similar to a robotic system, but with the actuators separated from the kinematic. The use of the SSD is as simple as follows: After planning of the intervention and rigid fixation of the cutting guide on the bone, the surgeon simply connects sequentially the screwdriver to all screws of the cutting guide.

To further maximise the ease of use and to avoid a mix-up of different screws, an identification means has been integrated into the positioning screws as well as into the smart screwdriver. For an automated identification of the screws different technologies have been analysed as position tracking, optical recognition or wired/wireless electronics.

A first prototype without screw identification has been used successfully on 4 cadaver knees. All guide positions could be adjusted automatically using the SSD. However, the absence of screw identification required that the surgeon follows indications given by the computer to turn screws sequentially.

A second prototype of the smart screwdriver has successfully been built up and is able to identify the different positioning screws in less than 1s with high reliability. The identification is realised as inductive coupling of different small resonance circuits that are integrated into the screw heads and the screwdrivers tip.

To adjust the cutting guide from neutral to the planned position, the screws have to be adjusted by 5 mm in average. The rotational speed of the current SSD implementation is 2 rounds per second, resulting in a mean time of about 3.5 s for each screw adjustment. The rotational accuracy of the screwdriver is ±5°. Taking into account a thread of the positioning screws of 0.7 mm, the theoretical translational error is about ±0.01 mm. Looking at the angular accuracy, the maximum distance of the screws of the current setup of the cutting block of 15 mm results in an angular error of less than ±0.05°.


R.J. Murphy Y. Otake J. Lepistö M. Armand

Introduction

The goal of this work is to develop a system for three-dimensional tracking of the acetabular fragment during periacetabular osteotomy (PAO) using x-ray images. For PAO, the proposed x-ray image-based navigation provides geometrical and biomechanical assessment of the acetabular fragment, which is unavailable in the conventional procedure, without disrupting surgical workflow or requiring tracking devices.

Methods

The proposed system combines preoperative planning with intraoperative tracking and near real-time automated assessment of the fragment geometry (radiographic angles) and biomechanics (contact pressure distribution over the acetabular surface). During PAO, eight fiducial beads are attached to the patient after incision and prior to performing osteotomy. Four of the beads attach to the iliac wing above the expected superior osteotomy (these are termed confidence points), and four attach on the expected fragment (denoted fragment points).

At least two x-ray images are obtained before and after osteotomy. In each set of images, image processing routines segment the fiducials and triangulate the 2D fiducial projections in 3D space. A paired-point registration between the confidence points triangulated from the two x-ray image sets aligns the imaging frames. We measured the transformation between the fragment points with respect to the confidence points to quantify the motion of the acetabular fragment. Applying an image-based 2D-3D registration to the measured acetabular transformation localises the reoriented acetabular fragment with respect to an anatomical coordinate system. We present the surgeon with visualisation and automatic estimations of radiographic angles and biomechanics of the reoriented acetabular fragment.

We conducted an experiment to evaluate feasibility and accuracy of the proposed system using a high density pelvic sawbone. Stainless steel beads were glued to the sawbone as fiducials. X-ray images were selected from cone-beam CT (CBCT) scans with an encoded motorised C-arm. Fiducial segmentation from reconstructed volumes of the CBCT scans provided a ground truth for the experiment.


S. Khamaisy E. Peleg G. Segal A. Hamad S. Luria

Purpose

The surgical treatment of scaphoid fractures consists of reduction of the fracture followed by stable internal fixation using a headless compression screw. Proper positioning of the screw remains technically challenging and therefore computer assisted surgery may have an advantage.

Navigation assisted surgery requires placement and registration of stable reference markers which is technically impossible in a small bone like the scaphoid. Custom made wrist-positioning devices with built-in reference markers have been developed for this purpose. The purpose of this study was to evaluate a different method of navigation assisted scaphoid fracture fixation. Temporary stabilisation with a pin of the scaphoid to the radius enables placement of the reference markers on the radius. Our hypothesis was that this method will achieve precise fracture fixation, superior to the standard free hand technique.

Methods

In 20 identical saw bone models with mobile scaphoids, the scaphoid was stabilised to the radius using one Kirschner wire (KW). An additional KW representing the fixating screw was placed either using the Mazor Renaissance Robotic System (MAZOR Surgical Technologies, Israel) or standard free hand technique. CT scans were performed prior to fixation and after fixation in order to plan the location of the KW and compare this planned location with the final result.


S. Luria Y. Schwartz R. Wollstein P. Emelif G. Zinger E. Peleg

Purpose

Knowing the morphology of any fracture, including scaphoid fractures, is important in order to determine the fracture stability and the appropriate fixation technique. Scaphoid fractures are classified according to their radiographic appearance, and simple transverse waist fractures are considered the most common. There is no description in the literature of the 3-dimensional morphology of scaphoid fractures. Our hypothesis was that most scaphoid fractures are not perpendicular to its long axis, i.e. they are not simple transverse fractures.

Methods

A 3-dimensional analysis was performed of CT scans of acute scaphoid fractures, conducted at two medical centers during a period of 6 years. A total of 124 scans were analysed (Amira Dev 5.3, Visage Imaging Inc). Thirty of the fractures were displaced and virtually reduced. Anatomical landmarks were marked on the distal radius articular surface in order to orient the scaphoid in the wrist. Shape analysis of the scaphoids and a calculation of the best fitted planes to the fractures were carried out implementing principal component analysis. The angles between the scaphoid's first principal axis to the fracture plane, articular plane and to the palmar-dorsal direction were measured. The fractures were analysed both for location (proximal, waist and distal) and for displacement.


H. Schöll M. Mentzel J. Gülke F. Gebhard M. Kraus

The internal fixation of scaphoid bone fractures remains technically difficult due to the size of the bone and its three- dimensional shape. Early rigid fixation, e.g with a screw, has been shown to support good functional outcome. In terms of stability of the fracture, biomechanical studies have shown a superior result with central screw placement in the scaphoid in comparison with an eccentric position, which can lead to delayed or non-union. Image-based navigation could be helpful for these cases. The main limitation of reference-based navigation systems is their dependence on fixed markers like used in modern navigation systems. Therefore it is limited in treatment of small bone fractures. In former experimental studies 20 artificial hand specimens were randomised into two groups and blinded with polyurethane foam: 10 were treated conventionally and 10 were image guided. For trajectory guidance a reduction of duration of surgery, radiation exposure and perforation rate compared to the conventional technique could be found. Accuracy was not improved by the new technique. The purpose of this study was to identify the possible advantages of the new guidance technique in a clinical setting.

In this prospective, non-randomised case series we tested the feasibility of the system into the accommodated surgical workflow. There was no control group. Three cases of scaphoid fractures were included. All of the patients were treated with a cannulated screw following K-wire placement via the percutaneous volar approach described. In addition, length measurements and screw sizes were determined using special features of the system. The performing surgeon and two attending assistant doctors (one assisting the surgical procedure, one handling the guidance system) had to rate the system following each procedure via a user questionnaire. They had to rate the system's integration in the workflow and its contribution to the success of the surgical procedure in percentages (0 %: totally unsuccessful; 100 %: perfect integration and excellent contribution). All of the clinical procedures were performed by the same surgeon.

The surgeons rated the system's contribution and integration as very good (91 and 94 % of 100 %). No adverse event occurred. An average of 1.3 trials ± 0.6 (1; 2) was required to place the K-wire in the fractured scaphoid bone. The dose-area product was 19 cGycm2 ± 3 (16; 22). The mean incision until suture time was 36.7 min ± 5.7 (30; 40). For clinical cases, the system was integrated and rated as very helpful by users.

The system is simple and can be easily integrated into the surgical workflow. Therefore it should be evaluated further in prospective clinical series.


M. Banger P.J. Rowe

There is an increasing prevalence of haptic devices in many engineering fields, especially in medicine and specifically in surgery. The stereotactic haptic boundaries used in Computer Aided Orthopaedic Surgery Unicomparmental Knee Arthroplasty (CAOS UKA) systems for assistive milling control can lead to an increase in the force required to manipulate the device; this study presented here has seen a several fold increase in peak forces between haptic and non-haptic conditions of a semi-active preoperative image system.

Orthopaedic Arthroplasty surgeons are required to apply forces ranging from large gripping forces to small forces for delicate manipulation of tools and through a large range of postures. There is also a need for surgeons to move around and position themselves to gain line of sight with the object of interest and to operate while wearing additional clothing such as the protective headwear and double gloves. These factors further complicate comparison with other ergonomic studies of other robotics systems. While robotics has been implemented to reduce fatigue in surgery one area of concern in CAOS is localised user muscle fatigue in high volume use.

In order to create the conditions necessary for the generation of fatigue in a realistic user experience, but in the time available for the participants, an extended period of controlled and prolonged cutting and manipulation of the robotic arm was needed. This pragmatic test requirement makes the test conditions slightly artificial but does indicate areas of high potential for fatigue when interacting with the system in high volume instances.

The surgeon-robotic system interaction was captured using 3 dimensional motion analysis and a force transducer embedded in the end effector of the robotic arm and modelled using an existing upper body model in Anybody software. The kinematic and force information allowed initial calculations of the interaction between the user and the Robotic system. Validation of the model was conducted using Electromyography assessment of activity and fatigue. Optimisation of the model sought to create an efficient cutting regime to reduce cutting time with reduced muscle force in an attempt to reduce users discomfort/fatigue while taking into account anthropometric variations in the users and minimising overall energy requirements, burr path length and maximum muscle force.

From the assessment of a small group of three surgeons with experience of the Robotic system there was little to no experience of above normal localised fatigue during small volume use of the system. Observation of these surgeons operating the robot state otherwise with examples of reactions to discomfort. There is also anecdotal evidence that fatigue becomes more problematic in higher volume work loads.


M. Banger P.J. Rowe M. Blyth

Time analysis from video footage gives a simple outcome measure of surgical practice against a measured model of use. The added detail that can be produced, over simply recording the usual surgical process data such as tourniquet times, allows us to identify and time the sequence of surgical procedures as stages, to describe issues, and the identification of idiosyncratic behaviours for review and comparison.

Makoplasty (Mako surgical corp. FL, US) partial knee operation times were compared using this technique with those from the Oxford (Biomet, IN, US) partial knee. Three experienced surgeons were observed over 19 Makoplasty procedures ([Consultant 1] 11, [Consultant 2] 5, [Consultant 3] 3) and 2 experienced surgeons over 11 Oxford partial knee procedures ([Consultant 1] 5, [Consultant 2] 6). Times were refined into separate stages that defined the major operative steps of both the Makoplasty and Oxford processes as used by the surgical team at the Glasgow Royal Infirmary, UK. The videos were reviewed for start and stop times for pre-defined actions that would be expected to be observed during each surgical process and from these stage lengths were calculated. For both the Oxford and Mako system 12 comparable stages were identified for comparison and the timing of the various episodes was tested for statistical significance using a Two-Sample, two tail, t-Test. assuming Equal Variances. [Stages: 1. Setup time, 2. Patient on table, 3. Skin incision, 4. Joint Prep, 5. Robot registration (Not in Oxford), 6. Tibial resection, 7. Femoral resection, 8. Trials, 9. Finishing, 10. Cementing and Washout, 11. Closure and dressing, 12. Off table]

The MAKOplasty procedures were on average longer than Oxfords by 27 minutes. This can largely be accounted for in the additional setup stage 4, where in addition to the usual joint preparation taking a couple of minutes approximately 17 minutes were spent in the MAKO cases undertaking image registration and in stage 5 where nearly five minutes were spent in setting up the robot in the MAKO cases.

In conclusion while operative times fell for the Makoplasties across the learning curve they remained elevated once the plateau was reached. It should be remembered that the surgeons had much less experience with the Makoplasty procedure and were undertaking a randomised clinical trial of outcome and hence were not minded to perform the surgery quickly but to the best of their ability and that this may account for some of the elongated surgical time. Indeed other Makoplasty surgeons report an average surgical time of 30–45 minutes per case and 6 cases per day. What is striking is that the additional steps of registration and robot positioning account for a large proportion of the differences and these are mitigated to some extent by quicker trialling of the implant and finishing of the cuts suggesting more confidence in the suitability of the cut surfaces. There is clearly a need to reduce the registration time to produce more cost effective surgeries.


T. Hawke M. Jakopec F. Rodriguez y Baena

In computer assisted orthopaedic surgery, intraoperative registration is commonly performed by fitting features acquired from the exposed bone surface to a preoperative virtual model of the bone geometry. In cases where the acquired spatial measurements are unreliable or have been inappropriately chosen, the registration result can degenerate. Current performance indicators, such as the root mean squared (RMS) error and the spatial distribution of the registered feature errors may not be sufficient to warn the surgeon of such a case.

In this study, statistical analysis is applied to the registration outcomes of perturbed variants of a collected point set. In this way, it is possible to assess the ability of the original set to represent the underlying surface, taking into account the distribution of the points as well as errors introduced during the acquisition process. Confidence measures are calculated to predict the reliability of the original registration result and therefore the robustness of the point set itself.

For proof of concept, this method has been tested in simulation with a CT-generated tibia model. The algorithm was used to identify the 10 best performing of a population of 1000 randomly generated point sets. All registration outcomes produced by these point sets were found to be superior to those resulting from sets of the same size produced manually using an optimised point-acquisition protocol. Preliminary results suggest that this method, alongside the standard RMS and residual point error distribution, may be used to provide the surgeon with a reliable indication of registration outcome in the operating room.


A. Motesharei P. Rowe J. Smith M. Blyth B. Jones A. MacLean

Unicompartmental knee arthroplasty (UKA) has been gaining popularity in recent years due to its perceived benefits over total knee replacements, such as greater bone preservation, reduced operating-room time, better postoperative range of motion and improved gait. However there have been failures associated with UKA caused by misalignment of the implants.

To improve the implant alignment a robotic guidance system called the RIO Robotic Arm has been developed by MAKO Surgical Corp (Ft. Lauderdale, FL). This robotic system provides real-time tactile feedback to the surgeon during bone cutting, designed to give improved accuracy compared to traditional UKA using cutting jigs and other manual instrumentation.

The University of Strathclyde in association with Glasgow Royal Infirmary has undertaken the first independent Randomised Control Trial (RCT) of the MAKO system against the Oxford UKA – a conventional UKA used in the UK. The trial involves 139 patients across the two groups.

At present the outcomes have been evaluated for 30 patients. 14 have received the MAKO unicompartmental knee arthroplasty and 16 the Oxford UKA. Both groups were seen 1 year post-operatively. Kinematic data was collected while subjects completed level walking using a Vicon Nexus motion analysis system. Three-dimensional hip, knee and ankle angles were compared between the two arthroplasty groups.

Our initial findings indicate that hip and ankle angles show no significant statistical difference, however there is a significant difference (p < 0.05) in the knee angles during the stance phase of gait. Data shows higher angles achieved by the MAKO group over the Oxford.

It would appear from our early findings that the MAKO RIO procedure with Restoris implants gives at least comparable functional outcome with the conventional Oxford system and may prove once our full sample is available for analysis to produce better stance phase kinematics with a more active gait pattern than the conventional Oxford procedure.

Further work includes analysing the data obtained from the patients in a number of other activities. These include a full biomechanical analysis of ascending and descending a flight of stairs, sit to stand and a deep knee lunge. The high demand/high flexion tasks in particular may reveal if there's an advantage to using the MAKO procedure over the Oxford. If there is a direct correlation between alignment and patient function then this effect could be more significant in the more demanding patient tasks.


D.F. Russell A.H. Deakin Q.A. Fogg F. Picard

Non-invasive assessment of lower limb mechanical alignment and assessment of knee laxity using navigation technology is now possible during knee flexion owing to recent software developments. We report a comparison of this new technology with a validated commercially available invasive navigation system.

We tested cadaveric lower limbs (n=12) with a commercial invasive navigation system against the non-invasive system. Mechanical femorotibial angle (MFTA) was measured with no stress, then with 15Nm of varus and valgus moment. MFTA was recorded at 10° intervals from full knee extension to 90° flexion. The investigator was blinded to all MFTA measurements. Repeatability coefficient was calculated to reflect each system's level of precision, and agreement between the systems; 3° was chosen as the upper limit of precision and agreement when measuring MFTA in the clinical setting based on current literature.

Precision of the invasive system was superior and acceptable in all conditions of stress throughout flexion (repeatability coefficient <2°). Precision of the non-invasive system was acceptable from extension until 60° flexion (repeatability coefficient <3°), beyond which precision was unacceptable. Agreement between invasive and non-invasive systems was within 1.7° from extension to 50° flexion when measuring MFTA with no varus / valgus applied. When applying varus / valgus stress agreement between the systems was acceptable from full extension to 20° & 30° knee flexion respectively (repeatability coefficient <3°). Beyond this the systems did not demonstrate sufficient agreement.

These results indicate that the non-invasive system can provide reliable quantitative data on MFTA and laxity in the range relevant to knee examination.


D.F. Russell A.H. Deakin Q.A. Fogg F. Picard

Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting.

We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation.

Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3mm).

These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology.


C. Belvedere A. Ensini A. Leardini V. Dedda F. Cenni A. Feliciangeli J.L. Moctezuma De La Barrera S. Giannini

INTRODUCTION

In computer-aided total knee arthroplasty (TKA), surgical navigation systems (SNS) allow accurate tibio-femoral joint (TFJ) prosthesis implantation only. Unfortunately, TKA alters also normal patello-femoral joint (PFJ) functioning. Particularly, without patellar resurfacing, PFJ kinematics is influenced by TFJ implantation; with resurfacing, this is further affected by patellar implantation. Patellar resurfacing is performed only by visual inspections and a simple calliper, i.e. without computer assistance.

Patellar resurfacing and motion via patient-specific bone morphology had been assessed successfully in-vitro and in-vivo in pilot studies aimed at including these evaluations in traditional navigated TKA.

The aim of this study was to report the current experiences in-vivo in two patient cohorts during TKA with patellar resurfacing.

MATERIALS AND METHODS

Twenty patients with knee gonarthrosis were divided in two cohorts of ten subjects each and implanted with as many fixed-bearing posterior-stabilised prostheses (NRG® and Triathlon®, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. Fifteen patients were implanted; five patients of the Triathlon cohort are awaiting hospital admission. TKAs were performed using two SNS (Stryker®-Leibinger, Freiburg-Germany). In addition to the traditional knee SNS (KSNS), the novel procedure implies the use of the patellar SNS (PSNS) equipped with a specially-designed patellar tracker.

Standard navigated procedures for intact TFJ survey were performed using KSNS. These were performed also with PSNS together intact PFJ survey. Standard navigated procedures for TFJ implantation were performed using KSNS. During patellar resurfacing, the patellar cutting jig was fixed at the desired position with a plane probe into the saw-blade slot; PSNS captured tracker data to calculate bone cut level/orientation. After sawing, resection accuracy was assessed using a plane probe. TFJ/PFJ kinematics were captured with all three trial components in place for possible adjustments, and after final component cementing. A calliper and pre/post-TKA X-rays were used to check for patellar thickness/alignment.


A. Ensini A. Leardini M. d'Amato F. Fusai C. Belvedere P. Barbadoro A. Timoncini S. Giannini

INTRODUCTION

In Total Knee Arthroplasty (TKA), the neutral overall limb alignment (NOLA), i.e. the mechanical alignment of the lower limb within 0°±3°, is targeted for achieving good clinical/functional results. The kinematic overall limb alignment (KOLA), which uses the axis through the centres of the femur posterior condyles modelled as cylinders, represents a novel approach for achieving better soft tissue balance.

Patient-specific instrumentation (PSI) is nowadays offered as an effective technology in TKA to obtain better lower limb alignments than those via conventional guides (CON). Although relevant results are still inconsistent, the benefits claimed include shorter operative time, reduced surgical instrumentation, and accurate preoperative planning.

The aim of this study was to report the preliminary clinical and radiological results of TKA patients operated via NOLA-PSI and KOLA-PSI. Comparisons between them and with the results obtained via NOLA-CON were performed.

PATIENTS AND METHODS

A four-centre randomised study on 144 patients has been designed to assess these three techniques. In each centre, 36 patients are planned to be operated, 12 per technique. Currently, in our centre 18 patients have been operated so far: 6 via NOLA-CON (Group A), 3 via NOLA-PSI (Group B), and 9 via KOLA-PSI (Group C). All patients were implanted with a cruciate-retaining TKA (Triathlon®, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patella resurfacing, those in PSI groups according to Otismed® imaging protocol. This includes pre-operative MRI scans at the hip, knee and ankle joints. Clinical evaluations were performed pre-operatively, at 45 days, and 3, 6 and 12 months post-operatively using the knee and functional IKSS (International Knee Society Score). At 45 days post-operatively a weight-bearing long leg radiograph was performed to measure possible differences between planned and implanted component alignment in patients operated via NOLA groups (A and B) and via KOLA group (C).


H. Enomoto T. Nakamura H. Shimosawa Y. Niki Y. Kiriyama T. Nagura Y. Toyama Y. Suda

Although proximal tibia vara is physiologically and pathologically observed, it is difficult to measure the varus angle accurately and reproducibly due to inaccuracy of the radiograph because of rotational and/or torsional deformities. Since tibial coronal alignment in TKA gives influence on implant longevity, intra- or extra-medurally cutting guide should be set carefully especially in cases with severe tibia vara. In this context, we measured the proximal tibial varus angle by introducing 3D-coordinate system.

Materials & Methods

Three-dimensional models of 32 tibiae (23 females, 9 males, 71.2 ± 7.8 y/o) were reconstructed from CT data of the patients undergoing CT-based navigation assisted TKA. Clinically relevant mid-sagittal plane is defined by proximal tibial antero-posterior axis and an apex of the tibial plafond. After the cross-sectional contours of the tibial canal were extracted, least-square lines were fitted to define the proximal diaphyseal and the metaphyseal anatomical axis. The proximal tibia vara was firstly investigated in terms of distribution of proximal anatomical axis exits at the joint surface. TVA1 and TVA2 were defined to be a project angle on the coronal plane between the metaphyseal tibial anatomical axis and the proximal diaphyseal anatomical axis, and that between the metaphyseal tibial anatomical axis and the tibial functional axis, respectively. The correlations of each angle with age and femoro-tibial angle (FTA) were also examined.

Results

The proximal anatomical axis exits distributed 4.3 ± 1.7 mm medially and 17.1 ± 3.4 mm anteriorly. TVA1 and TVA2 were 12.5 ± 4.5°(4.4?23.0°) and 11.8 ± 4.4° (4.4?22.0°), respectively. The correlations of FTA with TVA1 (r=0.374, p<0.05) and TVA2 (r=0.439, p<0.05) were statistically significant.


P.H. Richter T. Rahmanzadeh F. Gebhard G. Krischak M. Arand S. Weckbach M. Kraus

INTRODUCTION

Isolated injuries of the sacral bone are rare. The pathomechanism of these injuries are usually high velocity accidents or falls from large heights. The computer-assisted implantation of iliosacral screws (SI-screw) becomes more important in the treatment of dorsal pelvic ring fractures. The advantage of the minimal-invasive screw placement is the reduction of the non-union and deep wound infection rate. Another advantage of computer-navigated SI-screw placement is the reduction of intraoperative radiation for the patient and the surgical staff. The purpose of this study was to analyse the position of navigated iliosacral screws.

METHODS

In the study group 74 screws (49 patients) were included and radiologically analysed. All screws were implanted using 3D-navigation (BrainLAB Vector Vision, Brainlab, Germany). Navigation was always executed with the same 3D c-arm (ARCADIS Orbic 3D, Siemens, Germany) and navigation system. We determined the grade of perforation and angular deviation in the postoperative CT-scans in all screws. The classification was performed according to Smith et al in 4 grades. Grade 0 implies no perforation and grade 1 a perforation less than 2 mm. Grade 2 correlates a perforation of 2–4 mm and grade 3 a perforation of more than 4 mm. Furthermore the intra- and postoperative complications as well as the body-mass-index, the co-morbidities and the duration of radiation were documented. The statistical analysis was executed using Microsoft Excel 2003.


C.A. Anthony K. Duchman P. McCunniff S. McDermott M. Bollier D.R. Thedens B.R. Wolf J.P. Albright

While double-bundle anterior cruciate ligament (ACL) reconstruction attempts to recreate the two-bundle anatomy of the native ACL, recent research also indicates that double-bundle reconstruction more closely reproduces the biomechanical properties of the ACL and restores the rotatory and sagittal stability to the level of the intact knee that was not attainable with anatomic single-bundle reconstruction. Though double-bundle reconstruction provides these potential biomechanical benefits, it poses a significant challenge to the surgeon who must attempt to accurately place twice as many tunnels while avoiding tunnel convergence compared to single-bundle reconstruction. In addition, previous work has shown that tunnel malpositioning may cause grafts that fail to reproduce the native biomechanics of the ACL, increase graft tension in deep knee flexion, increase anterior tibial translation, and produce lower IKDC (International Knee Documentation Committee) scores.

We hypothesise that experienced surgeons without the use of computer-assisted navigation will place tunnels on the tibial plateau and lateral femoral condyle that more closely emulate the locations of the native anteromedial (AM) and posterolateral (PL) ACL bundles than inexperienced surgeons with the use of computer-assisted navigation.

A novice surgeon group comprised of three medical students each performed double-bundle ACL reconstruction using passive computer-assisted navigation on a total of eleven cadaver knees. Their individual results were compared to three experienced orthopaedic surgeons each performing the identical procedure without the use of computer-assisted navigation on a total of nine cadaver knees.

There were no significant differences in placement of either the AM or PL tunnels on the tibial plateau between novice surgeons using computer-assisted navigation and experienced surgeons without the use of computer navigation. On the lateral femoral condyle, novice surgeons placed the AM and PL tunnels significantly more anterior along Blumensaat's line on average compared to experienced surgeons. Both groups placed femoral AM and PL tunnels anterior to previously described AM and PL bundle positions.

Novice surgeons utilizing computer-assisted navigation and experienced surgeons without computer assistance place the AM and PL tunnels on the tibial side with no significant difference. On the lateral femoral condyle, novice surgeons utilising computer-assisted navigation place tunnels significantly anterior along Blumensaat's line compared to experienced surgeons without the use of computer navigation.


C.A Anthony P. McCunniff S. McDermott J.P. Albright

Variations in the pivot shift test have been proposed by many authors, though, a test comprised of rotatory and valgus tibial forces with accompanied knee range of motion is frequently utilised. Differences in applied forces between practitioners and patient guarding have been observed as potentially decreasing the reproducibility and reliability of the pivot shift test.

We hypothesise that a low-profile pivot shift test (LPPST) consisting of practitioner induced internal rotatory and anterior directed tibial forces with accompanied knee range of motion can elicit significant differences in internal tibial rotation and anterior tibial translation between the anterior cruciate ligament (ACL) deficient and ACL sufficient knee.

Fresh, frozen cadaver knees were used for this study. Four practitioners performed the LPPST on each ACL sufficient knee. The ACL of each knee was subsequently resected and each practitioner performed the LPPST on each ACL deficient knee. Our quantitative assessment utilised computer assisted navigation to sample (10Hz) the anterior translation and internal rotation of the tibia as the LPPST force vectors were applied. We subsequently pooled and averaged data from all four practitioners and analysed the entrance pivot (tibial reduction with knee range of motion from extension into flexion) and the exit pivot (tibial subluxation with knee range of motion from flexion into extension).

We observed a significant difference in anterior tibial translation and internal tibial rotation in the ACL deficient vs. ACL sufficient knees during both the entrance and exit pivot phases of the LPPST. The entrance pivot (n=140) was found to have an average maximum anterior tibial translation of 7.83 mm in the ACL deficient knee specimens compared to 1.23 mm in the ACL sufficient knee specimens (p<0.01). We found the ACL deficient knees to exhibit an average maximum internal tibial rotation of 12.38 degrees compared to 11.24 degrees in the ACL sufficient specimens during the entrance pivot (p=0.04). The exit pivot (n=120) was found to have an average maximum anterior tibial translation of 7.82 mm in the ACL deficient knee specimens compared to 1.44 mm in the ACL sufficient knee specimens (p<0.01). The ACL deficient knees exhibited an average maximum internal tibial rotation of 12.44 degrees compared to 11.13 degrees in the ACL sufficient knee specimens during the exit pivot (p=0.02).

Our results introduce a physical exam maneuver (LPPST) consisting of practitioner induced internal rotatory and anterior directed forces, with notable absence of valgus force, on the tibia while applying knee range of motion. Our results demonstrate that the LPPST can elicit significant anterior translation and internal rotary differences in an effort to differentiate between the ACL deficient and ACL sufficient knee. Our work will next seek to explore the clinical reproducibility of this physical exam maneuver.


N. Nakamura D. Iwana M. Kitada Y. Maeda T. Sakai

The occurrence of impingement can lead to instability, accelerated wear, and unexplained pain after THA. While implant and bony impingement were widely investigated, importance of soft tissue impingement was unclear. In the THA through posterior approach, it is known that posterior soft tissue repair can decrease the risk of dislocation. However, it is not known whether anterior soft tissue impingement by anterior hip capsule will influence hip ROM. The purpose of this study is to quantitatively measure the effect of anterior capsule resection on hip ROM in vivo during posterior approach THA using hip navigation system.

From June 2011, 26 hips (25 patients) that underwent primary THA using Stryker CT-based hip navigation system were the subjects. All were female osteoarthritis patients and the average age at the operation was 59 (47–76) years. Intraoperatively, acetabular cup and femoral stem placement were performed through posterior approach under the navigation system. After reduction of the joint, we measured hip ROM using the same navigation system. We measured them before and after the resection of anterior hip capsule and compared the difference.

After the resection of anterior hip capsule, the average increases of ROM were 0.7±3.5 degrees for flexion, 2.3±2.3 degrees for extension, 1.1±2.3 degrees for abduction and 2.1±2.9 degrees for external rotation at flexion 0 degree compared with ROM before the resection. However, it significantly increased 7.5±5.1 degrees for internal rotation at flexion 90 degree (range; −3–20, paired t-test p<0.001) and 6.1±5.5 degrees for internal rotation at flexion 45 degree (range; −4–18, p<0.001).

In this study, we used navigation system for assessment of soft tissue impingement. We found that during posterior approach THA, resection of anterior hip capsule brought about significant increase of ROM, especially in the direction of flexion with internal rotation. We also found that this procedure did not change ROM of flexion, extension, abduction and external rotation. These results indicated that, during THA through posterior approach, resection of anterior hip capsule could reduce the risk of posterior instability without increasing the risk of anterior instability.


T. Tsukeoka

Introduction

The midcortical line, the midline between the anterior and the posterior cortical walls has been reported as an intraoperative reference guide for reproducing the true femoral anteversion in cross-sectional computed tomography (CT) image study but we suspected that the version of the midcortical line on the cutting surface is different from that on the axial image. The three-dimensional (3D) CT-based preoperative planning software for THA enabled us to evaluate the cut surface of the femoral neck osteotomy. When we planned the straight non-anatomic stem placement in 20° of anteversion, we noticed that the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was coincident with the component torsion in almost all cases except those involving secondary osteoarthritis of the hip. Therefore we hypothesised that the T-line would provide an accurate reference guide for anteversion of the femoral component in THA. We performed this study to answer the question: which is the better intraoperative reference guide for reproducing the true femoral anteversion, the midcortical line or the T line?

Materials and methods

The institutional review board allowed a retrospective review of CT images of 33 normal femora (33 patients) in our CT database. We performed virtual THA using the non-anatomic straight stem on the 3D CT-based preoperative planning software at the two different cutting heights of 10mm or 15mm above the lesser trochanter. The anteversion of the stem implanted parallel to the T line or the midcortical line was measured. The true femoral neck anteversion was measured using the single CT slice method reported by Sugano.


RS. Khakha M. Norris A. Kheiran SK. Chauhan

Introduction

Computer Assisted Total Knee Arthroplasty (CATKA) has proven benefits of achieving reproducible and accurate component alignment with outcomes comparable to conventional jig based TKR. Optical trackers are required for assessment of alignment and are fixed via bone pins. This technique does present its own unique complications including fracture and infection at the pin- sites. We report our experience of a single surgeon series performing CATKA.

Objectives

Assess incidence of complications associated with Computer Assisted Total Knee Arthroplasty.


R.S. Khakha M. Norris A. Kheiran S.K. Chauhan

Introduction

Minimally invasive Computer Assisted Total Knee Arthroplasty (MICATKA) has benefits of reduced blood loss, shorter hospital stay, improved post-operative quadriceps function and enhanced post-operative recovery. Our study looked into these factors to compare if there was a significant difference when compared to conventional Computer Assisted Total Knee Arthroplasty (CATKA).

Objective

Compare radiological and clinical outcomes of MICATKA and CATKA at a minimum of 5 years.


R.S. Khakha M. Norris A. Kheiran S.K. Chauhan

Introduction

Unicondylar knee replacement (UKR) surgery is proven long term results in its benefit in medial compartment OA. However, its results are sensitive to component alignment with poor alignment leading to early failure. The advent of computer navigation has resulted in improved mechanical alignment, but little has been published on the outcomes of navigated UKR surgery. We present the results of 253 consecutive Computer Assisted UKR's performed by a single surgeon.

Objective

Assess clinical and radiological outcomes of Computer Assisted Unicondylar Knee Replacement at 5 years follow-up


R.S. Khakha M. Norris A. Kheiran S.K. Chauhan

Introduction

Computer assisted total knee replacement (CATKR) has been shown to give reproducible and accurate alignment of the mechanical axis. The benefits of the reproducible technique has been demonstrated in literature but there is little evidence of benefits in training junior surgeons in a clinical setting. We show our experience of CATKR performed by junior staff under supervision by the senior author, looking at component alignment and patient reported outcome measures.

Objectives

Assess radiological and clinical outcomes of Computer Assisted Total Knee Replacements performed by trainees.


H.M. Alvi R. Talati A.R. Patel M.A. Yaffe S.D. Stulberg

Introduction

Patient specific instrumentation (PSI) is an innovative technology in total knee arthroplasty (TKA). With the use of a preoperative MRI or CT scan, custom guide blocks are individually manufactured for each patient. Contrary to other TKA technologies such as computer-assisted surgery, PSI utilises measured resection technique rather than a primarily ligament balancing technique. This has the potential to negatively affect the operating surgeon's ability to achieve optimal soft tissue balancing, which is especially critical in patients with severe lower extremity malalignment. Despite early research suggesting that PSI is accurate, has a low learning curve, and can reduce operating room time, it remains unclear whether a surgeon using PSI can achieve optimal soft tissue balancing using a measured resection technique. The purpose of this study is to evaluate the efficacy of PSI in patients with severe preoperative limb alignment deformities.

Methods

Fifty PSI total knee arthroplasties were performed on 46 patients (21 male, 25 female) using the Zimmer NexGen Patient Specific Instrumentation system. Each patient included in the study had a minimum preoperative deformity of at least 10° varus or valgus measured on preoperative long leg standing radiographs, Zimmer preoperative software or both. Forty-three of the included knees had a varus deformity and 7 had a valgus deformity. Preoperative mechanical axis alignment measurements were obtained using the PSI preoperative planning software and were manually calculated using preoperative long leg standing radiographs. Postoperative mechanical axis alignment measurements were calculated using plain long leg standing radiographs. The Knee Society Scoring System was used to evaluate clinical and functional outcomes at 1 to 6 months postoperatively.


L. Angibaud X. Silver S. Gulbransen B. Stulberg

Clinical outcomes for total knee arthroplasty (TKA) are especially sensitive to lower extremity alignment and implant positioning. The use of computer-assisted orthopedic surgery (CAOS) can improve overall TKA accuracy. This study assessed the accuracy of an image-free CAOS guidance system (Exactech GPS, Blue-Ortho, Grenoble, FR) used in TKA.

A high-precision 3D scanner (Comet L3D, Steinbichler, Plymouth, MI) was used to scan seven knee models (MITA, Medical Models, Bristol, UK) and collect pre-identified anatomical landmarks prior to using the models to simulate knee surgery. The Exactech GPS was then used to acquire the same landmarks. After adjusting the Exactech GPS cutting block to match the targets, bone resections were performed, and the knee models were re-scanned. The 3D scans made before and after the cuts were overlaid and the resection parameters calculated using the pre-identified anatomical landmark data and advanced software (XOV & XOR, RapidForm, Lakewood, CO and UG NX, Siemens PLM, Plano, TX). Data sets obtained from the 3D scanner were compared with data sets from the guidance system. Given the accuracy of the 3D scanner, its measurements were used as the baseline for assessing CAOS system error.

The CAOS system bone resection measurement errors had an overall mean of less than 0.35 mm. The mean errors for joint angle measurement was less than 0.6°. Even considering the ranges, errors were no more than 1 mm for all bone resection measurements and no more than 1° for all joint angle measurements. The low variability is also supported by small SD values.

To our knowledge, this is the first study to use a high-resolution 3D scanner to assess the accuracy of surgical cuts made with image-free CAOS system assistance. Determining precise landmarks using CAOS for TKA has been shown to be of critical importance. For this reason, the anatomical landmarks used by the scanner and guidance system were carefully identified and prepared to ensure consistency.

The study demonstrated that the evaluated image-free CAOS system was able to achieve a high level of in-vitro accuracy (small mean errors) as well as a high level of precision (small error variability) when making femoral and tibial bone resections during TKA.


S. Khamaisy B. P. Gladnick D. Nam K. R. Reinhardt A.D. Pearle

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs.


J.G.G. Dobbe J.C. Vroemen S.D. Strackee G.J. Streekstra

A fracture of the distal radius may lead to malunion of bone segments, which gives discomfort to the patient and may lead to chronic pain, reduced range of motion, reduced grip strength and finally to early osteoarthritis. A treatment option to realign the bone segments is a corrective osteotomy. In this procedure the surgeon tries to improve alignment by cutting the bone at, or near, the fracture location and by fixating the bone segments in an improved position, using a plate and screws. Standard corrective osteotomy of the distal radius is most often planned using two orthogonal radiographs to find correction parameters for restoring the radial inclination, palmar tilt and ulnar variance, to normal. However, 2D imaging techniques hide rotations about the bone axis and may therefore cause a misinterpretation of the correction parameters.

We present a new technique that uses preoperative 3-D imaging techniques to plan positioning and to design a patient-tailored fixation plate that only fits in one way and realigns the bone segments as planned in six degrees of freedom. The procedure uses a surgical guide that snugly fits the bone geometry and allows predrilling the bone at specified positions, and cutting the bone through a slit at the preoperatively planned location. The patient-tailored plate fits the same bone geometry and uses the predrilled holes for screw fixation. The method is evaluated experimentally using artificial bones and renders realignment highly accurate and very reproducible (derr < 1.2 ± 0.8 mm and ϕerr < 1.8 ± 2.1°). In addition, the new method is evaluated clinically (n=1) and results in accurate positioning (derr ≤ 1.0 mm and ϕerr ≤ 2.6°).

Besides using a patient-tailored plate for corrective distal radius osteotomy, the method may be of interest for corrective osteotomy of other long bones, mandibular reconstruction and clavicular reconstruction as well. In all of these cases the contralateral side can equally be used as reference for reconstruction of the affected side.

The two-step method of predrilling and cutting using a surgical guide, followed by the utilisation of a patient-tailored plate for fixation and accurate 3D positioning at the same time, seems very easy to utilise during surgery, since it does not require complex navigation, robotic equipment or tracking tools. Custom treatment with a patient-tailored plate may reduce the reoperation rate, since repositioning is likely to be better than conventional malunion treatment using 2D imaging techniques and a standard anatomical plate. The patient-tailored plating technology is expected to have a great impact on future corrective osteotomy surgery.


P.L. Yen S.S. Hung S.W. Hsu

An intelligent bone cutting tool as well as a navigation system is of high potential to provide great assistance for the surgeons in computer assisted orthopedic surgery. In this paper we designed a coordinated controller for the surgical robot to perform bone cutting more safely, easily and fast compared with being performed by manual bone saw. Coordinated control is in an outer control loop and determines suitable parameters of the inner control loop of the robot. The inner control loop is an admittance controller for the master site and a compliance controller for the slave site. Coordinated control consists of three modes, i.e. automated cutting, cautious cutting and automated prevention depending on bone cutting conditions and human intention. In automated cutting mode, the coordinated control will set larger admittance gain and smaller compliance gain to provide an assistant force to the human for completion of bone cutting. In cautious cutting mode, smaller admittance gain and larger compliance gain will be set and a resistant force will be provided to the operator for micro progress of bone cutting. In emergence mode, the robot will stop the cutter going forward.

Experimental result shows that in automated mode of the proposed coordinated control was able to assist bone cutting at the same time to avoid undesired large cutting force and cutter breakage. The moving speed of cutter slowed down as the cutting forces increased due to the cutter hitting harder bone, thus alleviated sawblade bouncing up and achieved less deviation from designed cutting plane. In cautious cutting mode the cutting forces were magnified to be felt by the operator. The operator was able to perform micro progress of bone cutting with intensive monitoring of the cutting forces. This functionality is especially useful as the cutter approaches the critical area where the surgeon regards as dangerous region. The emergent mode was also successfully triggered by calculating the defined apparent admittance. The apparent admittance is more reliable than using the cutting force only in detection of cutting boundary.

A hand's on robot under coordinated control is demonstrated in conjunction with surgical navigation system in computer assisted orthopedic surgery. This paper experimentally showed that the coordinated control can effective provide assistive and resistant forces to achieve safe and accurate bone cutting in total knee arthroplasty.


H. Lin J.Q. Wang

Objective

Femoral shaft fracture treatment often results in mal-alignment and the high dosage of radiation exposure. The objective of this study is to develop a Parallel Manipulator Robot (PMR) on traction table to overcome these difficulties so as achieve better alignment for the fractured femur and reduce radiation to both patients and physicians.

Method

The distal platform of PMR is attached to the central pole on standard traction table by the boot adaptor. A leg model with soft tissue made by Pacific Research Laboratory, Inc. is flexed at the knee with patella on the top. A 2/3 circular ring, with 1/3 open circle down, fixed to the fractured distal femur with one trans-wire and one self-tapping screw, acting as adaptable stirrup fixing scheme. To secure proximal femur, an adapter is assembled on the traction table and fixed on the proximal femur. The distal femur is fixed to the 2/3 circular ring platform of PMR. Surgical planning is performed by first acquiring the bi-planar images from the C-Arm X-ray machine. After simulated fracture on 3-D femoral model is made, proximal and distal segments of the model will be superimposed with background bi-planar images. Finally the pre-fractured length and mechanical axis of 3-D femoral model will be restored. Afterwards, a table of schedule for length adjustments of six struts of PMR is generated. This length adjustment schedule is used to drive the PMR for fractured femur alignment and reduction. When reduction completed, a special designed device is used to fix the reduced femur. Then the PMR is removed from the traction table and the patient can be removed from the traction table.


K. Kress C. Anderson

Acetabular component positioning is highly correlated with total hip arthroplasty (THA) outcomes. Multiple reports however indicate that less than 50% of acetabular cups are placed within surgeon-desired ranges for abduction and anteversion angles when using conventional cup positioning techniques. Issues with improper placement include instability-dislocation, impingement and impact on range of motion, polyethylene wear, leg length discrepancy, and gait mechanics. Accuracy in placement of the acetabular component is complicated by the need to estimate cup impactor angles to create desired cup position. A low cost approach to THA using Image-based Ultrasonic Guidance (IUG) (Orthosensor, Sunrise, FL) coupled to existing surgical tools is presented. IUG utilises acoustic measurement techniques for achieving optimal component positioning and leg length. A precisely machined Hip Test Fixture (HTF) has been built to simulate the anatomical pelvis, acetabular cup, and femur to validate system accuracy.

The IUG was affixed to the HTF to demonstrate placement of the cup during THA. The HTF was loaded onto a 27-inch Graphic User Interface (GUI) providing three-dimensional CAD data of the HTF. Registration points included the Iliac Crest and 10 points around the acetabular cup. These points were mapped to the CAD data by the GUI. The HTF was set to 45° of abduction and 0° of version to begin testing. Abduction and version were measured over a +15° range in 1-degree increments while leg length and offset were measured over a +5mm range in 2mm increments. A high-resolution coordinate measurement machine (FaroArm EDGE) verified the accuracy and margin of error for inclination, version, leg length and offset at each increment.

The HTF provided a precise means for evaluating IUG system accuracy of simulated THA in a controlled environment. Acceptable margins of error were reported on the HTF: mean error for version was 0.36° (SD 0.02°; 0.25° to 0.38°); mean error for inclination was 1.04° (SD 0.52°; 0.48° to 1.66°); mean error for leg length and offset were respectively 0.36mm (SD 0.86mm; −0.65 to 1.55mm) and 0.41mm (SD 0.28; 0.05 to 0.80mm).

IUG provides a means for achieving acceptable precision and accuracy in component placement during THA as evaluated with the HTF. Further study is however necessary to correlate accuracy of IUG with clinical utility and short-term clinical outcomes.


Ph. Piriou E. Peronne

Rotational positioning of the femoral component during the realisation of a total knee arthroplasty is an important part of the surgical technique and remains a topic of discussion in the literature. The challenge of this positioning is important because it determines the anatomical result and its effect on the flexion gap and clinical outcome mainly through its impact on patellofemoral alignment. The intraoperative identification of the axis transepicondylar visually or by navigation is not reliable or reproducible. The empirical setting to 3 ° of external rotation, the procedure used to cut or dependent or independent is not adapted to the individual variability of knee surgery. Indeed, the angle formed by the posterior condylar axis and trans-epicondylar axis is subject to large individual variations.

The authors propose a novel technique, using the navigation of the trochlea to determine the rotation of the femoral component. The principle is to consider the rotation of the femoral implant as “ideal” when it makes a perfect superposition of the prosthetic trochlea with the native bony trochlea on patellofemoral view at 60 ° when planning the femur. The bottom of the prosthetic trochlea is well aligned with the trochlea groove, identified during the trochlear morphing, itself perpendicular to the trans-epicondylar axis. The authors hope to encourage centering patellofemoral joint prosthesis, thus favouring the original kinematics of the extensor apparatus.

The purpose of this study is to demonstrate firstly, that the navigation of the trochlea is a reliable and reproducible method to adjust the rotation of the femoral component relative to the trans-epicondylar axis taken as reference and the other, the rotation control by this method is not done at the expense of the balance gap in flexion.

It is a bi-centric study prospective, nonrandomised, including continuously recruited 145 patients in two French centres. All patients were included in the year 2010 and have all been revised three months and one year of surgery. The average age of patients was 71 years [53, 88]. It was made no selection of patients who have all been included consecutively in the study and in the two centres. In all cases, the rotation of the femoral component was determined by intraoperative navigation of the trochlea. The authors compared the alpha angle (angular divergence between the plane and the posterior bicondylar plane and trans-epicondylar axis) obtained by this method and that calculated on a pre-or postoperative scan. The authors also measured the space between femur and tibia internal and external side in flexion (90°) to assess the impact on the balance in flexion.

There is excellent agreement between the results obtained by the method of CT scan and the trochlear navigation technique. In addition, this technique allows to achieve a quadrilateral space gap in flexion. The authors found large individual variation in the distal femoral epiphyseal torsion (angle alpha). They demonstrate that the navigation of the trochlea is a reliable and reproducible method to adjust the rotation of the femoral component relative to the trans-epicondylar axis taken as reference and provides, concomitantly, a quadrilateral space gap in flexion.


J.G.G. Dobbe J.C. Vroemen R. Jonges S.D. Strackee G.J. Streekstra

After a fracture of the distal radius, the bone segments may heal in a suboptimal position. This condition may lead to a reduced hand function, pain and finally osteoarthritis, sometimes requiring corrective surgery.

The contralateral unaffected radius is often used as a reference in planning of a corrective osteotomy procedure of a malunited distal radius. In the conventional procedure, radiographs of both the affected radius and the contralateral radius have been used for planning. The 2D nature of radiographs renders them sub-optimal for planning due to overprojection of anatomical structures. Therefore, computer-assisted 3D planning techniques have been developed recently based on CT images of both forearms.

The accuracy of using the contralateral forearm for CT based 3D planning the surgery of the affected arm and the optimal strategy for planning have not been studied thoroughly.

To estimate the accuracy of the planned repositioning using the contralateral forearm we investigated bilateral symmetry of corresponding radii and ulnae using 3-dimensional imaging techniques. A total of 20 healthy volunteers without previous wrist injury underwent a volumetric computed tomography scan of both forearms. The left radius and ulna were segmented to create virtual 3 dimensional models of these bones. We selected a distal part and a larger proximal part from these bones and matched them with a mirrored CT-image of the contralateral side. This allowed estimation of the accuracy by calculation of relative displacements (Δx, Δy, Δz) and rotations (Δψx, Δψy, Δψz) required to align the left bone with the right bone segments as a reference. We also investigated the relationship between longitudinal length differences in radius and ulna and utilised this relationship to arrive at an optimal planning of the length of the affected radius after surgery.

Relative differences in displacement and orientation parameters after planning based on the contralateral radius were (Δx, Δy, Δz): −0.81±1.22 mm, −0.01±0.64 mm, and 2.63±2.03 mm; and (Δψx, Δψy, Δψz): 0.13°±1.00°, −0.60°±1.35°, and 0.53°±5.00°. The same parameters for the ulna were (Δx,Δy, Δz): −0.22±0.82 mm, 0.52±0.99 mm, 2.08±2.33 mm; and (Δψx, Δψy, Δψz): −0.56°±0.96°, −0.71°±1.51°, and −2.61°±5.58°. The results also point out that there is a strong linear relationship between absolute length differences (Δz) of the radius and ulna among the individuals.

Since we observed substantial length difference of the longitudinal bone axes of both forearms in healthy individuals, including the length difference of the adjacent forearm bones in the planning turned out to be useful in improving length correction in computer-assisted planning of radius or ulna osteotomies. The improved planning markedly reduces length positioning variability, (from 2.9± 2.1 mm to 1.5 ± 0.6 mm). We expect this approach to be valuable for 3-D planning of a corrective distal radius osteotomy. Awareness of the level of bilateral symmetry is important in reconstructive surgery procedures when the contralateral unaffected side is used as a reference for planning and evaluation. Bilateral asymmetry may introduce length errors into this type of preoperative planning that can be reduced by taking into account the concomitant ulnae asymmetry.


M. Pink T. Valousek M. Miklas

Introduction

The aim of our study was to compare the radiographic alignment unicompartmental knee arthroplasty (UKA) with using conventional non-navigation technique and computer-assisted navigation technique. Our study was focused on bearing alignment on clinical outcome of knee.

Materials and Methods

In our department we have performed between January 2005 and December 2012 106 UKA. All patients were examined clinically and radiologically before and after operation. There were implanted two types of UKA, 67 of UKA were performed by The PRESERVATION™ (DePuy) with navigation and 39 UKA Oxford® Partial Knee (Biomet.) were performed by conventional technique. In our study we have evaluated 104 of medial UKA divided to groups, 65 implantation of The PRESERVATION™ and 39 implantation of Oxford® Partial Knee UKA. We have evaluated 101 patients, 61 women, 40 men, average age 66,5 (50–82) years. Firstly we performed measurement of parameters determine alignment UKA. These values were written down and the deviation of norm was established. Results were divided in two groups, one with values of normal range and the second beyond normal range. Values of all UKA were matched with clinical outcome postoperatively. This assessment was performed by The Knee Society Clinical Rating System (Knee score).


N. Confalonieri A. Manzotti S. Aldè

INTRODUCTION

Despite clear clinical advantages Unicompartimetal Knee Replacement (UKR) still remain a high demanding and less forgiving surgical procedure. Different Authors in literature pointed out how in coronal tibial malalignment beyond 3° as well as tibial slope beyond 7° increase the rate of aseptic failure. Likewise, overcorrection in the coronal plain is a well recognised cause of failure because of an overweighting on the controlateral compartment. Furthermore it has been shown how in UKR surgery even using short narrow intramedullary guide this can cause errors in both coronal planes. Computer assisted surgery has been proposed to improve implant positioning in joint replacement surgery with no need of intramedullary guide. Likewise more recently Patient Specific Instrumentation (PSI) has been suggested as a new technology capable of new advantages such as shorter surgical times and lower blood losses maintaining at least the same accuracy. Aim of this prospective study is to present comparing 2 groups of UKRs using either a computer assisted technique or a CT based PSI.

MATERIALS AND METHODS

Since January 2010 54 patients undergoing UKR because of medial compartment arthritis were prospectively enrolled in the study. Before surgery patients were alternatively assigned to either computer-assisted alignment (group A) or PSI group (group B). In the group A (27 knees) the implant (Sigma, Depuy Orthopaedics Inc, Warsaw, Indiana, USA) was positioned using a CT-free computer assisted alignment system specifically created for UKR surgery (OrthoKey, Delaware, USA USA). In group B (27knees) the implant (GMK uni, Medacta, Castel San Pietro, Switzerland) was performed using a CT-Based PSI technology (MyKnee, Medacta, Castel San Pietro, Switzerland). In both the groups all the implants were cemented and using always a fixed metal backed tibial component. The duration of surgery and all the complications according to Kim classification were documented in all cases. Six months after surgery each patient had long-leg standing anterior-posterior radiographs and lateral radiographs of the knee. The radiographs were assessed to determine the Frontal Femoral Component angle (FFC), the Frontal Tibial Component angle (FTC), the Hip-Knee-Ankle angle (HKA) and the sagittal orientation (slope) of both tibial and femoral component. The number and percentage of outliners for each parameter was determined. In addition the percentage of patients from each group with all 5 parameters within the desired range was calculated. Furthermore at the latest follow-up the 2 groups were clinically assessed using KSS and Functional score.


A. Manzotti S. Aldè N. Confalonieri

INTRODUCTION

A preoperative planning for accurately predicting the size and alignment of the prosthetic components may allow to perform a precise, efficient and reproducible total knee replacement. The planning can be carried out using as a support digital radiographic images or CT images with three-dimensional reconstruction. Aim of this prospective study is to evaluate and compare the accuracy of two different types of pre-operative planning, in determining the size of the femoral and tibial component in total knee arthroplasty performed with Patient Specific Instrument (PSI). The two compared techniques were: digital radiography and “CT-Based”.

MATERIALS AND METHODS

A prospective study was conducted to compare the accuracy in predicting the size of the prosthetic components in total knee replacement in 71 patients diagnosed with primary and symptomatic osteoarthritis of the knee. Inclusion criteria was “Easy Knee”: BMI ≤ 35, varus/valgus deviation ≤15° and residual flexion of the knee ≥ 90°. Pre-operatively all the patients underwent to the same standard protocol including digital radiographs with calibration and a CT scan. A dedicated IMPAX digital software (Agfa-Gevaert, NV, USA) was used to template the radiographs. The CT-based planning was performed on 3D reconstruction of CT scans of 3 joints: hip, knee and ankle, as established in standardised protocol to build up patient specific cutting mask (MyKnee, Medacta, Castel S. Pietro, Switzerland). All the surgeries were performed by 2 senior Authors (M.A and N.C.) using the same implant and the definitive component sizes implanted were registered and compared with the sizes suggested by both planning techniques considering also the range of error. Results analysis was carried out using nonparametric tests.


M. Kraus C. Dehner C. Riepl G. Krischak F. Gebhard H. Schöll

In orthopaedic surgery, as in many other surgical fields, there is a clear tendency towards the use of minimally invasive procedures. These techniques are increasingly being implemented almost routinely for procedures such as spine and pelvis surgery. However, for fracture treatment and for applications involving small bones, such as hand and foot surgery, these systems are hardly ever used. We introduce a new system for image based guidance in traumatology.

We included 20 patients with a fracture of the fifth metatarsal. They were randomised on admission into two groups. Ten patients in the metatarsal group were operated conventionally and ten were operated with the assistance of a new image guidance system. This system is based on 2D-fluoro images which are acquired with a conventional c-arm and are transferred to the system workstation. After detecting marked tools, it can be used to display trajectories for K-wire guidance in the c-arm shot.

The average duration of surgery (time from incision to suture) in the image-based group was 12.7 minutes ± 5.5 (min. 6, max. 23), in the conventional group it was 17 minutes ± 6.5 (min. 7, max. 28) (p=0.086). The average duration of radiation was 18 seconds ± 8.5 (min. 6, max 36) in the image-based group vs. 32.4 seconds ± 19.4 (min. 12, max. 66) in the conventional group (p=0.057). An average of 4.7 C-arm shots ± 2 (min 2, max 9) were necessary in the image-based group to position the K-wire. For the conventional group, 8.2 shots ± 2.3 (min 4, max 12) were used (p=0.0073). It took 1.6 trials ± 0.7 (min.1, max. 3) to position the K-wire for the image-based procedures, in the conventional group 2.7 trials ± 0.9 (min. 1, max 4) were necessary (p=0.0084). There were no malfunctions or adverse events in any of the image-based navigational cases. No screws needed to be replaced in the image-based group. In the conventional group, two screws were replaced intra-operatively because they were too short in the control c-arm shot, and the screw threads did not bridge the fracture gap completely, leading to insufficient compression.

In this pilot study with only a small sample size, the image-based guidance system could be integrated into the existing surgical workflow and was used for applications, where existing navigation systems are not commonly used. The technology gives the surgeon additional information and can reduce the number of trials for perfect implant positioning. This potentially increases the safety of the surgical procedure and spares intact bone substance which is essential for the footing of implants in small bones and fragment fixation. Whether these factors contribute to a reduction in complications or revision rate must be confirmed in larger prospective studies.


D.C. Hansen R.M. Palmer K. Botkin R.C. Wasielewski S.K. Kusuma

Medial unicompartmental knee arthroplasty (UKA) for isolated medial knee arthritis is a highly successful and efficacious procedure. However, UKA is technically more challenging than total knee arthroplasty (TKA). Research has shown that surgical technical errors may lead to high early failure rates. Haptic robotic systems have recently been developed with the goal of improving accuracy, reducing complications, and improving overall outcomes. There is little research comparing robotic-assisted UKA to standard UKA. The goal of this study was to compare clinical and radiographic data for matched cohorts who received robotic-arm assisted UKA or standard instrumentation UKA.

We performed a non-randomised, retrospective review of 30 robotic-arm assisted UKA and 32 manual UKA performed by single fellowship-trained joint arthroplasty surgeon (SKK) over 2.5 years. All procedures completed through a medial parapatellar approach. All components were cemented. All tibial components were a metal-backed onlay design. Average follow-up was 10.1 months (range 5–36). A full clinical/hospital chart review of demographic, intra- and post-operative measures was performed. Radiographic analysis of pre- and post-op images evaluating sagital and coronal alignment, and component positioning was performed by single observer (DCH), using OsiriX imaging system (Pixmeo; Geneva, Switzerland). Radiographs were available for analysis in 28 robotic-assisted and 30 manual patients. Statistical analysis was performed using SPSS v. 20. Comparison between group means was performed as well as calculation of variance in component placement within groups.

No demographic differences were seen between groups. Operative time was significantly longer in robotic-assisted UKA compared to the manual group. Minimal clinical post-op differences were seen between groups. The robotic group showed some early advantage in ambulation/ROM during inpatient stay. This ROM difference reversed at 2 weeks post-op. Continued medial-sided knee pain was reported more commonly in robotic group. Radiographic results showed no difference between groups in pre-op mechanical alignment. The robotic group was significantly more accurate at recreating femoral axis. Accuracy in recreation of tibial slope/ was similar between groups. Accuracy of the tibial component in the coronal plane was not significantly different between groups. The robotic group did have significantly larger variance in coronal alignment of the tibial component. Medial overhang of tibial component was significantly greater and more variable in the manual group. Non-significant decrease in resection depth found in robotic group.

There were minimal clinical and radiographic differences between techniques. Clinically, both cohorts did very well. Radiographically, both groups had quite accurate placement of components, with the most obvious difference being the increased tibial component overhang in the manual group. The increased variance in tibial component alignment in the robotic group is likely due to the ability to more specifically alter the resection to fit the patient's specific anatomy. Overall, our data suggests that the purported benefits of robotic UKA may be obviated in the hands of a surgeon with training and experience in manual UKA implantation.


X. Kang D. R. Wilson A. J. Hodgson

This paper presents a methodology for measuring the femoro-pelvic joint angle based on in vivo magnetic resonance imaging (MRI) images taken under weight-bearing conditions. We assess the reproducibility of angle measurements acquired when the subject is asked to repeatedly assume a reference position and perform a voluntary movement.

We scanned a healthy subject in a lying position in a 3T MRI scanner to obtain high resolution (HR) images including two transverse T1-weighted TSE sequence scans at the pelvis and knee and a sagittal T1-weighted dual sense scan at the hip joint. We then scanned the same subject in a weight-bearing configuration in a 0.5T open MRI scanner to obtain related low resolution (LR) images of the femur and acetabulum. Four scan cycles were obtained with the subject being removed and reinserted between cycles in the Open MRI scanner. In each cycle, a block was inserted (up position) and removed (down position) under the subject's foot.

The femur and acetabulum bone models were manually segmented and the models from the LR (sitting) images were registered to the HR (supine) images. The femoroacetabular angles relative to the LR scanning plane for four cycles were calculated. The femoral angle relative to the scanner were quite repeatable (SD < 0.9°), the pelvic angles less so (SD ∼2.6–4.3°). The hip flexion angle ranged from 23°–34° in the down and up positions, respectively, so the block induced a mean angle change in the flexion direction of approximately 11° (SD = 1.7°).

We found that the femoral position could be accurately re-acquired upon repositioning, while the pelvic position was notably more variable. Limb position changes induced by inserting a block under the subject's foot were consistent (standard deviations in the relative attitude angles under 2°). Overall, our measurement method produces plausible measures of both the femoroacetabular angles and the changes induced by the block, and the reproducibility of relative joint changes is good.

ACKNOWLEDGMENTS: Dr. Kang was supported by the National Science and Engineering Research Council of Canada (NSERC) through a Postdoctoral Fellowship and conducted her research at the Centre for Hip Health and Mobility at Vancouver General Hospital, Canada.


M.K. Merz F.C. Bohnenkamp K.N. Sadr W.M. Goldstein A.C. Gordon

Introduction

Risks and benefits of bilateral total knee arthroplasty (TKA), whether simultaneous, sequential single-staged, or staged is a topic of debate. Similarly, computer-assisted navigation for TKA is controversial regarding complications, cost-effectiveness, and benefits over conventional TKA. To our knowledge, no studies have compared computer-assisted and conventional techniques for sequential bilateral TKA. We hypothesise that the computer-assisted technique has fewer complications.

Methods

We retrospectively reviewed 40 computer-assisted and 36 conventional bilateral sequential TKAs from 2007–2011 with 1 year follow-up for complications. Groups were matched by age, gender, body mass index (BMI), Charlson Comorbidity Index (CCI), and American Society of Anesthesiologists Classification (ASA). Pearson's Chi-square, Fisher's exact test, and independent samples t-test were used to compare groups.


M.S. Hefny J.F. Rudan R.E. Ellis

INTRODUCTION

Understanding bone morphology is essential for successful computer assisted orthopaedic surgery, where definition of normal anatomical variations and abnormal morphological patterns can assist in surgical planning and evaluation of outcomes. The proximal femur was the anatomical target of the study described here. Orthopaedic surgeons have studied femoral geometry using 2D and 3D radiographs for precise fit of bone-implant with biological fixation.

METHOD

The use of a Statistical Shape Model (SSM) is a promising venue for understanding bone morphologies and for deriving generic description of normal anatomy. A SSM uses measures of statistics on geometrical descriptions over a population. Current SSM construction methods, based on Principal Component Analysis (PCA), assume that shape morphologies can be modeled by pure point translations. Complicated morphologies, such as the femoral head-neck junction that has non-rigid components, can be poorly explained by PCA. In this work, we showed that PCA was impotent for processing complex deformations of the proximal femur and propose in its place our Principal Tangent Component (PTC) analysis. The new method used the Lie algebra of affine transformation matrices to perform simple computations, in tangent spaces, that corresponded to complex deformations on the data manifold.


S. Luria Y. Schwartz R. Wollstein P. Emelif G. Zinger E. Peleg

Purpose

Knowing the morphology of any fracture, including scaphoid fractures, is important in order to determine the fracture stability and the appropriate fixation technique. Scaphoid fractures are classified according to their radiographic appearance, and simple transverse waist fractures are considered the most common. There is no description in the literature of the 3-dimensional morphology of scaphoid fractures. Our hypothesis was that most scaphoid fractures are not perpendicular to its long axis, i.e. they are not simple transverse fractures.

Methods

A 3-dimensional analysis was performed of CT scans of acute scaphoid fractures, conducted at two medical centres during a period of 6 years. A total of 124 scans were analysed (Amira Dev 5.3, Visage Imaging Inc). Thirty of the fractures were displaced and virtually reduced. Anatomical landmarks were marked on the distal radius articular surface in order to orient the scaphoid in the wrist. Shape analysis of the scaphoids and a calculation of the best fitted planes to the fractures were carried out implementing principal component analysis. The angles between the scaphoid's first principal axis to the fracture plane, articular plane and to the palmar-dorsal direction were measured. The fractures were analysed both for location (proximal, waist and distal) and for displacement.