Purpose: Surgical techniques must be evaluated before proceeding with widespread use. The evaluation system is usually copied after that used for drugs, relying on randomised trials. This system fails however to assess one dimension, i.e. quality control. The purpose of the present study was to demonstrate the usefulness of an evaluation technique taking into account the capacity to control the quality of a surgical procedure and determine the reliability, reproducibility, and controllability of the technique. This method of evaluation was applied to computer-assisted surgery for total knee arthroplasty. Material and methods: Computer-assisted surgery based on 3D bone reconstruction was used for 78 knees. The main outcome assessment criterion was the mechanical axis from the centre of the femoral head to the centre of the ankle. The desired alignment was between 3° varus and 3° valgus. Alignments were measured continuously by an independent operator. A Cusum curve was drawn over time and tested after each operation to determine whether the procedure under evaluation could be continued. The same method was applied to the position of the individual femoral and tibial implants setting the limits at two degrees around the perpendicular mechanical axis (AP view). Results: The mechanical axis was between 3° varus and 3° valgus in 91% of the knees. The continuous evaluation curve showed that the procedure was under control throughout the trial. There was a learning curve that plateaued at 27 knees. Evaluation of the position of the individual implants showed a trend towards femur valgus over time which was compensated by a trend towards tibial varus. Discussion: Industrial quality control procedures are well established and widely used. The goal of this work was to apply the same quality control methodology to a surgical procedure. Before undertaking a randomised trial this type of evaluation can affirm that the procedure is well controlled and that using an innovating technique under these conditions does not expose patients to undue risks

Orthopaedic surgery residents typically learn total knee arthroplasty (TKA) through an apprenticeship-type model, which is a necessarily slow process. If residents could learn the required technical and cognitive skills more quickly, they could make better use of reduced hours in the operating room, surgeons could teach at a higher level, patients could have shorter operating times with better outcomes, and the healthcare system would have reduced costs and better-trained surgeons. Surgical skills courses, using artificial bones, have been shown to improve technical and cognitive skills significantly within a couple of days. Computer-assisted surgery (CAS) provides real-time feedback and component position planning, leading to improved alignment and a shorter learning curve. Combining these two approaches challenges the participants to consider the same task in different contexts, promoting cognitive flexibility. We designed a hands-on educational intervention for junior residents incorporating a conventional tibiofemoral TKA station, two different tibiofemoral CAS stations and a conventional and CAS patellar resection station. The same implant system was used in all cases. Both qualitative and quantitative analyses were performed. Qualitatively, structured interviews before and after the course were analysed for recurring themes. Quantitatively, subjects were evaluated on their technical skills in a timed conventional TKA test before and after the course, and on their knowledge and error-detection skills after the course. Their performance was compared to senior residents who performed only the testing. Four themes emerged: increased confidence, improved awareness, deepening knowledge and changed perspectives. The residents' attitudes to CAS changed from negative before the course to neutral or positive after the course. They expected it to be difficult to use and found that it was easy. They originally distrusted the system, but came to think they would use it for their most difficult cases. The junior resident group improved their task completion rate from 23% to 75% of tasks (p<0.01), compared to 45% of tasks completed by the senior resident group. As a result of the course, the residents will be more aware what to focus on in the operating room. High impact educational interventions, promoting cognitive flexibility and including real-time feedback from computer-assisted surgery simulations, would benefit trainees, surgeons, the healthcare system and patients

Introduction and Aims: Computer-assisted surgery may significantly improve the accuracy of total knee arthroplasty. The reproducibility of acquiring points that facilitate the computer generation of joint morphology which is fundamental for guiding surgery remains unclear. The aim of this study was to assess inter- and intra-operator reproducibility using a computer guidance system. Method: Three surgeons were involved in this study, who under instruction from a proprietary computer system acquired points on a sawbone model of the knee that correlated with specific anatomic landmarks. This process was performed five times each and repeated on another identical model. The points acquired allowed the computer to generate a knee joint model that predicted size, orientation and alignment of the knee joint. Inter- and intra-operator comparisons of the size of the prostheses, the amount of resection, the rotation of the prostheses, and the relationship of the epicondylar to the posterior femoral condylar axis were made. Results: This study was commenced one day after an eight-hour hands-on workshop describing the use of the computer guidance system. The computer system accurately recorded the acquisition of points on a sawbone model. There was little difference in the time taken by each surgeon to acquire the points. Although, all iterations of point acquisition were performed sequentially, there was no clear reduction in the time taken for the process of acquisition. Despite the repetitive use of identical sawbone models, all three surgeons demonstrated significant variation within their own and between each others’ acquisitions. This resulted in variations of prosthetic sizes, amounts of bone resection and rotation of implants. The consistency at which certain indices differed suggested a specific bias between surgeons that may reflect technique or interpretation of anatomic landmarks, e.g. relationship between the epicondylar and posterior condylar axes. Conclusion: An important reason for the variation may be the difference in interpretation of the location of anatomic landmarks. This may have a significant impact on the generation of computer model for guiding subsequent surgery. Clear definitions of landmarks and a robust education program is required if computer assisted surgery is to be accurate and meaningful

The clinical success and long-term outcomes of total knee arthroplasty (TKA) depend not only on the accuracy of femoral and tibial components positioning, but also on the restoration of a proper mechanical axis (MA). Coronal and rotational mal-alignment may affect significantly the final result of a knee replacement. Patient specific cutting guides and intra-operative Computer-Assisted Surgery (CAS) have recently been introduced as options to improve implant alignment during TKA. The purpose of this study was to compare the alignment accuracy and implant positioning of Patient Matched technique to CAS system in patients with primary TKA. A cohort of 68 consecutive patients who underwent TKA was enrolled for this study: 34 patients received a TKA using CAS system while 34 patients received a TKA using a MRI-based Patient Matched system. Mechanical axis and kinematics were digitally measured pre- and post-operatively in all knees using the intra-operative navigation system but data were blinded for the operating surgeon in the Patient Matched group. A post-operative CT-scan evaluation was performed in all patients to analyse the prosthetic components alignment (coronal, sagittal and axial alignment according to Perth Protocol from CT-scan). CT-scan measurements were used as landmarks as this tool is considered the gold standard. MA, posterior tibial slope (PTS) and femoral component rotation (FCR) in CAS group were compared to data of Patient Matched group. All patients also underwent a clinical evaluation with Knee Society Score (KSS) and Knee injury and Osteoarthritis Outcome Score (KOOS) at 6 and 12 months of follow up. KSS, KOOS and range of motion were comparable in the two groups after surgery. Operative time was significantly shorter in the Patient Matched group. No differences were found regarding complications rate. Mean angles, respectively for CAS and Patient Matched groups, were the following: MA was 1,7° (SD 0,9°) vs 0.8° (SD 2.1°); PTS was 3.1° (SD 0.9°) vs 3.4° (SD 2.1°); FCR was 1.5° (SD 2.2°) vs 1.36° (DS 1.2°). The outcomes of the CT scan evaluation were the following: MA was 1.5° (SD 0.8°) vs 1.0° (DS 1.5°); PTS was 2.3° (SD 0.8°) vs 3.0° (SD 2.6°); FCR was 0.4° (SD 0.8°) vs 0.2° (SD 0.3°). MA was within 3° of neutral alignment in 94% of patients for CAS group and in 97% of knees for Patient Matched group. After a short follow up, there weren't statistically significant differences between CAS and Patient Matched techniques as regards clinical and functional scores. Both the systems achieved the goal of neutral alignment within 3° of varus and valgus. We only observed greater precision for Patient Matched technique in optimizing femoral component rotation. Actually it is unpredictable if this difference may determine long term effects. Patient Matched technique and CAS for TKA surgery will certainly continue to have an impact in the future. Studies are needed to define which technique is better, in terms of long term results, failure rate and cost-effectiveness

Computer-assisted surgery (CAS) is a tool developed to allow accurate limb and implant alignment in total knee arthroplasty [TKA]. The strength of the technology is that it allows the surgeon to assess soft tissue balance and ligament laxity in flexion and extension. The accuracy of this ligament balancing technology depends upon an accurate determination of femoral component size. This size is established with intraoperative surface registration techniques. Customised instrumentation (CI) is a measured resection technique in which component size is established on preoperative 3D MRI reconstructions. The purpose of this study is to determine how these two computer-based technologies compare with regard to the accuracy with which femoral component size is established in TKA. 67 TKA were performed using CI and 30 TKA were performed using CAS by a single surgeon. CI-predicted and CAS-predicted femoral component size were compared to actual component selection. The process by which CI and CAS perform an anatomic registration was evaluated. The CI and CAS systems accurately predicted surgeon-selected femoral component size in 89% and 43% of cases, respectively (p<0.001). The discrepancy between predicted and actual femoral component size with CI and CAS was 0.1 and 0.8 sizes, respectively (p<0.001). The maximum deviation between predicted and actual femoral component size was greater in CAS than in PMI (three sizes versus one size, respectively). The anterior cortex cut was flush in 92% of CI cases. The rotation profile was consistent with Whiteside's line in 95% of CI cases. The CI system was both more accurate and more precise than the CAS navigation system in predicting femoral component size in TKA. CI utilises preoperative MR imaging to generate femoral component sizing based on optimizing medial-lateral fit with a measured posterior femoral bone resection. CAS utilises surface registration techniques based on anatomic site registration that may be subject to intraoperative measurement error due to difficult visualization (femoral epicondyles), inherent subjectivity (Whiteside's line) or anatomic variation (hypoplastic posterior condyles). CI bases implant sizing solely on reproducing an anatomical fit and a measured resection technique, whereas CAS attempts to balance an anatomic fit with optimal soft tissue balancing. In this study, the surgeon's final component selection was more likely to be in accordance with the CI rather than the CAS sizing algorithm. The CI system was capable of accurate femoral component placement in TKA. This study suggests that intraoperative surface registration may not be as accurate as preoperative 3D MRI reconstructions for establishing optimal femoral component sizing. Surgeons using intraoperative navigation based surface registration need to be aware of this when making femoral component size selection, establishing ligament balance, and determining femoral rotation

Introduction

Malalignment of total knee arthroplasty components may affect implant function and lead to decreased survival, regardless of preferred alignment philosophy – neural mechanical axis restoration or kinematic alignment. A common technique is to set coronal alignment prior to adjusting slope. If the guide is not maintained in a neutral position, adjustment of the slope may alter coronal alignment. Different implant systems recommend varying degrees of slope for ideal function of the implant, from 0–7°. The purpose of this study was to quantify the change in coronal alignment with increasing posterior tibial slope comparing two methods of jig fixation.

Introduction

Acquiring adaptive soft-tissue balance is one of the most important factors in total knee arthroplasty (TKA). However, there have been few reports regarding to alteration of tolerability of varus/valgus stress between before and after TKA. In particular, there is no enough data about mid-flexion stability. Based on these backgrounds, it is hypothesized that alteration of varus/valgus tolerance may influence post-operative results in TKA. The purpose of this study is an investigation of in vivo kinematic analyses of tolerability of varus/valgus stress before and after TKA, comparing to clinical results.

Purpose: One of the biomechanical objectives of total knee arthroplasty (TKA) is to achieve a mechanical femorotibial axis of 180°. Frontal angulation greater or equal to 7° is a factor of poor implant survival. The development of computer-assisted navigation systems has led to the discovery of new concepts: dynamic goniometry, quantitative evaluation of ligament balance. The purpose of this study was to evaluate the influence of the rotational position of the femoral implant and its variation during flexion.

Material and methods: We reviewed the files of 50 patients who underwent surgery between October 2001 and December 2002 for computer-assisted implantation (Orthopilot(r)). We studied femorotibial axis at 0°, 30°, 60° and 90° before the bone cuts, after the tibial cuts and at the end of the procedure after definitive fixing of the implants.

Results: The population, mean age 70 years, was evenly distributed: 17 valgum and 32 varum. The mean femorotibial axis at the end of the operation with the definitive implants in place was 0° in extension with balanced ligaments (±2°) and more often increased varus at 30°, 60° and 90° flexion.

Discussion: External rotation of the femoral piece was not systematic. Certain normally aligned knees in extension after the tibial cut presented significant varus in flexion, probably due to external rotation of the femoral epiphysis. On the contrary, knees with internal rotation of the femoral epiphysis, irrespective of the cause, showed a trend to valgus during flexion. Using external rotation of the femoral implant systematically for both knee morphotypes cannot be done without deteriorating the ligament balance in certain patients.

Conclusion: The advent of navigation systems for TKA has led to the discovery of new concepts such as dynamic goniometry. This has enabled study of femorotibial alignment in flexion, the working position of the knee during walking. This study showed that systematic external rotation of the femoral implant for TKA is not appropriate for all patients.

Computer assisted surgery (CAS) is used in trauma surgery to reduce radiation and improve accuracy but it is time consuming. Some trials for navigation in small bone fractures were made, but they are still experimental. One major problem is the fixation of the dynamic reference base for navigation. We evaluated the benefit of a new image based guidance-system (Surgix®, Tel Aviv, Israel) for fracture treatment in scaphoid bones compared to the conventional method without navigation. The system consists of a workstation and surgical devices with embedded radio opaque markers. These markers as well as the object of interest must be on the same C-arm shot. If a tool is detected in an image by the attached workstation additional information such as trajectories are displayed in the original fluoroscopic image to serve the surgeon as aiming device. The system needs no referencing and no change of the workflow.

For this study 20 synthetic hand models (Synbone®, Malans, Switzerland) were randomised in two groups. Aim of this study was a central guide-wire placement in the scaphoid bone, which was blindly measured by using postoperative CT-scans. Significant distinctions related to the duration of surgery, emission of radiation, radiation dose, and trials of guide-wire positioning were observed.

By using the system the surgery duration was with 50 % shortened (p = 0.0054) compared to the conventional group. One reason might be the significant reduction of trials to achieve a central guide-wire placement in the bone (p = 0.0032). Consequently the radiation exposure for the surgeon and the patient could be shortened by reduction of radiation emission (p = 0.0014) and radiation dose (p = 0.0019).

By using the imaged based guidance system a reduction of surgery duration, radiation exposure for the patient and the surgeon can be achieved. By a reduced number of trials for achieving a central guide-wire position the risk of weakening the bone structure can be minimised as well by using the system. The system seems helpful where navigation is not applicable up to now. The surgical workflow does not have to be chanced.

Introduction: Computer-assisted TKA improves alignment accuracy; however few articles cite any clinical benefit over conventional TKA. The author’s experience and outcomes with CAS for TKA including ligament balancing with a spring loaded tensioning device is reported.

Methods: This is a retrospective review of prospectively collected data on 1005 TKAs (975 had OA) with 464 cases using Depuy^® LCS^® CompleteTM Rotating Platform and 474 cases using Depuy^® P.F.C^® SigmaTM Rotating Platform. Seventy-six were conventional TKAs and 929 were CAS TKAs. Average follow up was 17 months. Outcome variables included radiographic alignment, Knee Society Scores, and complications.

Results: Eighty-eight percent of CAS TKAs were placed within three degrees of neutral mechanical axis. Eighty-one percent were placed within three degrees of optimal sagittal tibial component angle. Ninety-two percent were placed within three degrees of optimal coronal tibial component angle.

Mean pain score improved 39.4 points, Knee Score improved 47.8 points, and the functional component improved 17.1 points. The pain score improvement for CAS was 39.2 compared to 33.0 for conventional knees (p< 0.002). The Knee Score improvement for CAS was 48.3 compared to 41.4 for conventional knees (p< 0.013). The functional component improvement was not significant between CAS and conventional TKA. When CAS is utilized along with the spring loaded tensioning device for ligament balancing, manipulation rates dropped to 7% (p< 0.01). There were a total of thirteen infections, three deep infections (0.3%) and ten superficial infections (1%). There were no fractures from the pin sites, and no patients were revised for instability.

Conclusion: Our series showed a statistically significant improvement in pain and Knee Society Scores compared with conventional TKA. In addition, CAS resulted in excellent radiographic alignment and well balanced knees with the spring loaded tensioning device. Furthermore, improved radiographic alignment is likely to increase implant survivorship and provide further cost savings. With continued use of CAS, long term studies may show significant beneficial clinical effects.

Background:

Numerous studies have reported the importance of acetabular component positioning in decreasing dislocation rates, the risk of liner fractures, and bearing surface wear in total hip arthroplasty (THA). The goal of improving acetabular component positioning has led to the development of computer-assisted surgical (CAS) techniques, and several studies have demonstrated improved results when compared to conventional, freehand methods. Recently, a computed tomography (CT)-based robotic surgery system has been developed (MAKO™ Robotic Arm Interactive Orthopaedic System, MAKO Surgical Corp., Fort Lauderdale, FLA, USA), with promising improvements in component alignment and surgical precision. The purpose of this study was to compare the accuracy in predicting the postoperative acetabular component position between the MAKO™ robotic navigation system and an imageless, CAS system (AchieveCAS, Smith and Nephew Inc., Memphis, TN, USA).

In recent years, some attempts have been made to develop a method that generates finite element (FE) models of the femur and pelvis using CT. However, due to the complex bone geometry, most of these methods require an excessive amount of CT radiation dosage. Here we describe a method for generating accurate patient-specific FE models of the total hip using a small number of CT scans in order to reduce radiation exposure.

A previously reported method for autogenerating patient-specific FE models of the femur was extended to include the pelvis. CT osteodensitometry was performed on 3 patients who had hip replacement surgery and patient-specific FE models of the total hip were generated. The pelvis was generated with a new technique that incorporated a mesh morphing method called ‘host mesh fitting’. It used an existing generic mesh and then morphed it to reflect the patient specific geometry. This can be used to morph the whole pelvis, but our patient dataset was limited to the acetabulum. An algorithm was developed that automated all the procedures involved in the fitting process.

Average error between the fitted mesh and patient specific data sets for the femur was less than 1mm. The error for the pelvis was about 2.5mm. This was when a total 18 CT scans with 10mm gap were used – 12 of the femur, and 6 of the pelvis. There was no element distortion and a smooth element surface was achieved.

Previously, we reported a new method for automatically generating a FE model of the femur with as few CT scans as possible. Here we describe a technique that customizes a generic pelvis mesh to patient-specific data sets. Thus we have developed a novel hybrid technique which can generate an accurate FE model of the total hip using significantly less CT scans.

An automated method of generating FE models for the total hip with reduced CT radiation exposure will be a valuable clinical tool for surgeons.

Purpose: To determine if use of CAS in TKA improves postoperative mechanical axis alignment and component position as compared to use of standard surgical instrumentation.

Method: 200 patients were prospectively randomized to TKA utilizing CAS navigation vs. standard surgical technique. Two surgeons performed all procedures utilizing a subvastus approach, the BrainLab navigation system and posterior cruciate substituting implants. Postoperative mechanical axis alignment was measured on full length standing radiographs and component placement on CT (Perth protocol). Two independent raters measured radiographic angles. The variation in mechanical axis measures were compared between the two treatment groups using a two-sided permutation test.

Results: Surgery has been completed on all 200 patients with patient demographics similar among the two treatment groups. Median tourniquet time was increased in the navigation group (82 mins versus 57 mins, p < 0.001). Radiographic analysis of the first 100 patients showed the standard deviation of the post-operative mechanical axis measurements to be 22% lower in the navigation group than the standard surgical instrumentation group (2.4 vs. 3.0), marginally significant (p = 0.055). Optimal mechanical axis alignment (to within 3 degrees or less) was achieved in 75% of patients with navigation and in 68% of patients with standard surgical instrumentation. Analysis of all 200 pts will be completed shortly as well as results of component placement based on postoperative CT.

Conclusion: Based on analysis of the first 100 patients, use of CAS in TKA marginally statistically improved mechanical axis alignment precision compared to standard surgical technique.

Purpose: This study attempted to determine if the form of feedback provided by a computer-based navigation technique improves the learning of the placement of cannulated screws across a femoral neck fracture in the surgical trainee.

Method: A prospective, randomized, appropriately powered, and controlled study involving 39 surgical trainees (first-year residents and fourth-year medical students) with no prior experience in surgically managing femoral neck fractures were used in the study. After a training session, participants underwent a pretest by performing the surgical task on a simulated hip fracture using fluoroscopic guidance. Immediately after, 20 participants were randomized into undergoing a training session using a conventional fluoroscopy-guided technique while the other participants were randomized into undergoing a training session using a computer-based navigation technique. Immediate post-tests and retention tests (4 weeks later) were performed. A transfer test was used to assess the impact of the type of training on surgical performance – after performing the retention test, each group repeated the task but used the other technique to guide them (i.e. those trained with fluors-copy used computer navigation and vice versa).

Results: Screw placement was equal and to the level of an expert surgeon with either training technique during the post-, retention, and transfer tests. Participants that were trained with computer navigation took fewer attempts to position hardware and used less fluoroscopy time than those that trained with fluoroscopy. When participants that trained with computer navigation reverted to conventional fluoroscopic technique at the transfer test, more fluoroscopy time and dosage was used. Participants that trained with fluoroscopy used less fluoroscopy time and took fewer attempts to position hardware when they subsequently used computer navigation to perform the task during the transfer test.

Conclusion: Computer navigation does not harm the learning of surgical novices in this basic orthopaedic surgical skill. Training with computer navigation minimizes radiation exposure and decreases the number of attempts to perform the task. No compromise in learning occurs if a surgical novice trains with one type of technology and transfers to using the other.

The Bernese periacetabular osteotomy (PAO) described by Ganz, et al. is a commonly used surgical intervention in hip dysplasia. PAO is being performed more frequently and is a viable alternative to hip arthroplasty for younger and more physically active patients. The procedure is challenging because pelvic anatomy is prohibitive to visibility and open access and requires four X-ray guided blind cuts around the acetabulum to free it from the hemi-pelvis. The crucial step is the re-orientation of the freed acetabulum to correct the inadequate coverage of the femoral head by idealy rotating the freed acetabular fragment.

Diagnosis and the decision for surgical intervention is currently based upon patient symptoms, use of two-dimensional (2D) radiographic measurements, and the intrinsic experience of the surgeon. With the advent of new technologies allowing three-dimensional reconstructions of hip anatomy, previous two-dimensional X-ray definitions have created much debate in standardizing numerical representations of hip dysplasia. Recent work done by groups such as Arminger et al. have combined and expanded two-dimensional measurements such as Center-Edge (CE) angle of Wiberg, Vertical-Center-Anterior margin (VCA) angle, Acetabular Anteversion (AcetAV) and applied them to three-dimensional CT rendering of hip anatomy. Further, variability in pelvic tilt is a confounding factor and has further impeded measurement translatability.

Computer assisted surgery (CAS) and navigation also called image-guided surgery (IGS) has been used in clinical cases of PAO with mixed results. The first appearing study of CAS/IGS in PAO was conducted by Langlotz, et. al 1997 and reported no clinical benefit to using CAS/IGS. However, they did conclude that the use of CAS/IGS is undoubtedly useful for surgeons starting this technically demanding procedure. This is supported by a more recent study done by Hsieh, et. al 2006 who conducted a two year randomised study of CAS/IGS in PAO and concluded its feasibility to facilitate PAO, but there was not an additional benefit when conventional PAO is done by an experienced surgeon. A study done by Peters, et. Al 2006 studying the learning curve necessary to become proficient at PAO found that “The occurrence of complications demonstrates a substantial learning curve” and thus makes a compelling argument for the use of CAS/IGS.

A major obstacle to navigation and CAS/IGS revolves around consistency, intra-operative time and ease of use. Custom made guides and implants may help circumvent these limitations. The use of CAS/CAM in developing custom made guides has been proven very successful in areas of oral maxillofacial surgery, hip arthroplasty, and knee replacement surgeries. Additionally, a significant study in the development of rapid prototyping guides in the treatment of dysplastic hip joints was done by Radermacher et. al 1998. They describe a process of using CAS/CAM within the operational theatre using a desktop planning station and a manufacturing unit to develop what they termed as “templates” to carry out a triple osteotomy.

Our group is evaluating and developing strategies in PAO using CAS/IGS and more recently using CAS and computer aided modeling (CAM) to develop custom made guides for acetabular positioning. Our first study (Burch et al.) focused on CAS/IGS in PAO using cadavers and yielded small mean cut (1.97± 0.73mm) and CE angle (4.9± 6.0) errors. Our recent study used full sized high-resolution foam pelvis models (Sawbones^®, Vashon, Washington) and used CAS/IGS to carry out the pelvic cuts and CAS/CAM to develop a acetabular positioning guide (APG) by rapid prototyping. The CAS/IGS pelvic cuts results were good (mean error of 3.18 mm ± 1.35) and support our and other studies done using CAS/IGS in PAO. The APG yielded high accuracy and was analysed using four angles with an overall mean angular error of 1.81 (0.55⁰)and individual angulation was as follows: CE 0.83° ± 0.53, S-AC 0.28° ± 0.19, AcetAV 0.41° ± 0.37, and VCA 0.68° ± 0.27. To our knowledge this is the first developed APG for PAO.

The APG we developed was to demonstrate the concept of using a positioning guide to obtain accurate rotation of the acetabular fragment. For a clinical application a refined and sleeker design would be required. Further, because working space within the pelvis is extraordinary constrained, once fitted the APG would need to remain and serve as an implantable cage capable of holding bone graft. A potential material is polyetheretherketone (PEEK). Customised PEEK implants and cages have been established in the literature and is a potential option for PAO. The benefits of an implant not only serve to constrain the acetabular fragment in the ideal position based upon the pre-operative plan, but may also provide the structural support for rotations not other wise possible.

Though CAS/IGS is a proven viable option, we envision a potentially simpler method for PAO, the use of a cut guide and an acetabular positioning implant. Using customized guides and implants could potentially circumvent the need for specialised intra-operative equipment and the associated learning curves, by providing guides that incorporate the pre-operational plan within the guide, constraining the surgeon to the desired outcome.

Recently, several preliminary reports have been issued on the application of computer assistance to bone tumour surgery. Surgical navigation systems can apply three-dimensional images such as CT and MR images to intraoperative visualization. Although CT is better at describing cortical bone status, MRI is considered the best method for defining the extent of marrow involvement for bone tumours and for planning surgical resection in bone tumour surgery. There have been a few reports on the application of MR imaging to navigation-assisted bone tumour surgery through CT–MR image fusion. However, the CT–MRI fusion technique requires additional costs and exposure of the patient to radiation from the preoperative CT, as well as additional time for image fusion. Above all, the image fusion process is a kind of registration (image to image registration) that inevitably leads to registration error. Herein we describe a new method for the direct application of MR images to navigation-assisted bone tumour surgery as an alternative to CT–MRI fusion. Six patients with an orthopaedic malignancy were employed for this method during navigation-assisted tumour resection. Resorbable pin placement and rapid 3-dimensional spoiled gradient echo sequences made the direct application of MR images to computer-assisted bone tumour surgery without CT–MR image fusion possible. A paired-point registration technique was employed for patient-image registration in all patients. It took 20 min on average to set up the navigation (range 15 to 25 minutes). The mean registration error was 0.98 mm (range 0.4 to 1.7 mm). On histologic examination, distances from tumours to resection margins were in accord with preoperative plans. Mean duration of follow-up was 25.8 months (range 18 to 32 months). No patient had a local recurrence or distant metastasis at the last follow-up. Direct patient-to-MRI registration is a very useful method for bone tumour surgery, permitting the application of MR images to intraoperative visualization without any additional costs or exposure of the patient to radiation from the preoperative CT scan

The hip centre (HC) in Computer Assisted Orthopedic Surgery (CAOS) can be determined either with anatomical (AA) or functional approaches (FA). AA is considered as the reference while FA compute the hip centre of rotation (CoR). Four main FA can be used in CAOS: the Gammage, Halvorsen, pivot, and least-moving point (LMP) methods. The goal of this paper is to evaluate and compare with an in-vitro experiment (a) the four main FA for the HC determination, and (b) the impact on the HKA.

The experiment has been performed on six cadavers. A CAOS software application has been developed for the acquisitions of (a) the hip rotation motion, (b) the anatomical HC, and (c) the HKA angle. Two studies have been defined allowing (a) the evaluation of the precision and the accuracy of the four FA with respect to the AA, and (b) the impact on the HKA angle.

For the pivot, LMP, Gammage and Halvorsen methods respectively: (1) the maximum precision reach 14.2, 22.8, 111.4 and 132.5 mm; (2) the maximum accuracy reach 23.6, 40.7, 176.6 and 130.3 mm; (3) the maximum error of the frontal HKA is 2.5°, 3.7°, 12.7° and 13.3°; and (4) the maximum error of the sagittal HKA is 2.3°, 4.3°, 5.9°, 6.1°.

The pivot method is the most precise and accurate approach for the HC localisation and the HKA computation.

A number of advantages of unicondylar arthroplasty (UKA) over total knee arthroplasty in patients presenting osteoarthritis in only a single compartment have been identified in the literature. However, accurate implant positioning and alignment targets, which have been shown to significantly affect outcomes, are routinely missed by conventional techniques. Computer Assisted Orthopaedic Surgery (CAOS) has demonstrated its ability to improve implant accuracy, reducing outliers. Despite this, existing commercial systems have seen extremely limited adoption. Survey indicates the bulk, cost, and complexity of existing systems as inhibitive characteristics. We present a concept system based upon small scale head mounted tracking and augmented reality guidance intended to mitigate these factors.

A visible-spectrum stereoscopic system, able to track multiple fiducial markers to 6DoF via photogrammetry and perform semi-active speed constrained resection, was combined with a head mounted display, to provide a video-see-through augmented reality system. The accuracy of this system was investigated by probing 180 points upon a 110×110×50 mm known geometry and performing controlled resection upon a 60×60×15 mm bone phantom guided by an overlaid augmented resection guide that updated in real-time.

The system produced an RMS probing accuracy and precision of 0.55±0.04 and 0.10±0.01 mm, respectively. Controlled resection resulted in an absolute resection error of 0.34±0.04 mm with a general trend of over-resection of 0.10±0.07 mm.

The system was able to achieve the sub-millimetre accuracy considered necessary to successfully position unicondylar knee implants. Several refinements of the system, such as pose filtering, are expected to increase the functional volume over which this accuracy is obtained. The presented system improves upon several objections to existing commercial CAOS UKA systems, and shows great potential both within surgery itself and its training. Furthermore, it is suggested the system could be readily extended to additional orthopaedic procedures requiring accurate and intuitive guidance.

Despite being demonstrably better than conventional surgical techniques with regards to implant alignment and outlier reduction, computer navigation systems have not faced widespread adoption in surgical operating rooms. We believe that one of the reasons for the low uptake stems from the bulky design of the optical tracker assemblies. These trackers must be rigidly fixed to a patient's bone and they occupy a significant portion of the surgical workspace, which makes them difficult to use. In this study we introduce the design for a new optical tracker system, and subsequently we evaluate the tracker's performance. The novel tracker consists of a set of low-profile flexible pins that can be placed into a rigid body and individually deflect without greatly affecting the pose estimation. By relying on a pin's stiff axial direction while neglecting lateral deviations, we can gain sufficient constraint over the underlying body. We used an unscented Kalman filter based algorithm as a recursive body pose estimator that can account for relative marker displacements. We assessed our tracker's performance through a series of simulations and experiments inspired by a total knee arthroplasty. We found that the flexible tracker performs comparably to conventional trackers with regards to accuracy and precision, with tracking errors under 0.3mm for typical operating conditions. The tracking error remained below 0.5mm during pin deflections of up to 40mm. Our algorithm ran at computation speeds greater than real-time at 30Hz which means that it would be suitable for use in real-time applications. We conclude that this flexible pin concept provides sufficient accuracy to be used as a replacement for rigid trackers in applications where its lower profile, its reduced invasiveness and its robustness to deflection are desirable characteristics.