Aims

Unicompartmental knee arthroplasty (UKA) is a bone-preserving treatment option for osteoarthritis localized to a single compartment in the knee. The success of the procedure is sensitive to patient selection and alignment errors. Robotic arm-assisted UKA provides technological assistance to intraoperative bony resection accuracy, which is thought to improve ligament balancing. This paper presents the five-year outcomes of a comparison between manual and robotically assisted UKAs.

Objectives

This study reports on a secondary exploratory analysis of the early clinical outcomes of a randomised clinical trial comparing robotic arm-assisted unicompartmental knee arthroplasty (UKA) for medial compartment osteoarthritis of the knee with manual UKA performed using traditional surgical jigs. This follows reporting of the primary outcomes of implant accuracy and gait analysis that showed significant advantages in the robotic arm-assisted group.

The knee joint displays a wide spectrum of laxity, from inherently tight to excessively lax even within the normal, uninjured population. The assessment of AP knee laxity in the clinical setting is performed by manual passive tests such as the Lachman test. Non-invasive assessment based on image free navigation has been clinically validated and used to quantify mechanical alignment and coronal knee laxity in early flexion. When used on cadavers the system demonstrated good AP laxity results with flexion up to 40°. This study aimed to validate the repeatability of the assessment of antero-posterior (AP) knee joint laxity using a non-invasive image free navigation system in normal, healthy subjects.

Twenty-five healthy volunteers were recruited and examined in a single centre. AP translation was measured using a non-invasive navigation system (PhysioPilot) consisting of an infrared camera, externally mounted optical trackers and computer software. Each of the volunteers had both legs examined by a single examiner twice (two registrations). The Lachman test was performed through flexion in increments of 15°. Coefficients of Repeatability (CR) and Interclass Correlation Coefficients (ICC) were used to validate AP translation. The acceptable limits of agreement for this project were set at 3mm for antero-posterior tibial translation.

The most reliable and repeatable AP translation assessments were at 30° and 45°, demonstrating good reliability (ICC 0.82, 0.82) and good repeatability (CR 2.5, 2.9). The AP translation assessment at 0°, 15°, 75° and 90° demonstrated moderate reliability (ICC ≤ 0.75), and poor repeatability (CR ≥3.0mm).

The non-invasive system was able to reliably and consistently measure AP knee translation between 30° and 45° flexion, the clinically relevant range for this assessment. This system could therefore be used to quantify abnormal knee laxity and improve the assessment of knee instability and ligamentous injuries in a clinic setting.

Knee osteoarthritis results in pain and functional limitations. In cases where the arthritis is limited to one compartment of the knee joint then a unicondylar knee arthroplasty (UKA) is successful, bone preserving option. UKA have been shown to result in superior clinical and functional outcomes compared to TKA patients. However, utilisation of this procedure has been limited due primarily to the high revision rates reported in joint registers. Robotic assisted devices have recently been introduced to the market for use in UKA. They have limited follow up periods but have reported good implant accuracy when compared to the pre-operative planned implant placement.

UKA was completed on 25 cadaver specimens (hip to toe) using an image-free approach with infrared optical navigation system with a hand held robotically assisted cutting tool. Therefore, no CT scan or MRI was required. The surface of the condylar was mapped intra operatively using a probe to record the 3 dimensional surface of the area of the knee joint to be resurfaced. Based on this data the size and orientation of the implant was planned. The user was able to rotate and translate the implant in all three planes. The system also displays the predicted gap balance graph through flexion as well as the predicted contact points on the femoral and tibial component through flexion. The required bone was removed using a bur. The depth of the cut was controlled by the robotically controlled freehand sculpting tool.

Four users (3 consultant orthopaedic surgeon and a post-doctoral research associate) who had been trained on the system prior to the cadaveric study carried out the procedures. 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 RMS angular error was 2.34°. The maximum femoral RMS translational error across all directions was up to 1.61mm. The maximum tibial RMS angular error was 2.60°. The maximum tibial RMS translational error across all directions was up to 1.67mm.

In conclusion, the results of this cadaver study reported low RMS errors in implant position placement compared to the plan. The results were comparable with those published from clinical studies investigating other robotic orthopaedic devices. Therefore, the freehand sculpting tool was shown to be a reliable tool for cutting bone in UKA and the system allows the surgeon to plan the placement of the implant intra operatively and then execute the plan successfully.

Unicompartmental knee arthroplasty (UKA) has been gaining popularity in recent years due to its perceived benefits over total knee arthroplasty (TKA), such as greater bone preservation, reduced operating-room time, better post-operative range of motion and improved gait. However there have been failures associated with UKA caused by misalignment of the implants that have lead to revisions. To improve the implant alignment a robotic guidance system called the RIO Robotic Arm has been developed by MAKO Surgical Corp (Ft. Lauderdale, FL), which is 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 RCT trial of the MAKO system against the Oxford unicompartmental knee arthroplasty – a conventional UKA used in the UK. Motion analysis was used in order to obtain a quantitative assessment of their movement. The results from a total of 51 patients (23 MAKO, 28 Oxford) that underwent a one year post-operative biomechanical assessment were investigated.

Motion analysis showed that during level walking the MAKO group achieved a higher knee excursion during the highest flexion portion of the weight bearing stage of the gait cycle (foot-strike to mid-stance) compared to the Oxford group (18.6° and 15.8° respectively). This difference was statistically significant (p-value = 0.03). Other knee excursion values that were compared were from mid-stance to terminal stance, and overall knee flexion. No statistically significant differences were seen in either of these measurements. A subsequent comparison of both MAKO and Oxford groups with a matched normal cohort (50 patients), demonstrated that there wasn't a statistically significant difference between the MAKO group and the normal knees during mean knee excursion from foot-strike to mid-stance (18.6° and 19.5° respectively, p-value 0.36). However the Oxford group, with a lower knee excursion was found to be significantly different to our normal control group (15.8° and 19.5° respectively, p-value < 0.001).

This suggests that the robotic-assisted knees behaved more similarly to normal gait during this phase of the gait cycle than those of the conventional group. While significant differences in gait were found between the Oxford and MAKO groups, further work is required to determine if this results in improved knee function that is perceptible to the patient.

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.

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.

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.

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.

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.

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.

This RCT compared electromagnetic (EM) navigated and conventional total knee arthroplasty (TKA) in terms of clinical and functional outcomes. 200 patients (navigated=102, conventional=98) were recruited. Oxford Knee Scores (OKS) and the American Knee Society Score (AKSS) were recorded pre operation, 3 and 12 months after surgery. Post operative (coronal, sagittal and rotational) alignment was analysed from 3D CT scans taken 3 months after surgery. An objective functional assessment was completed using electrogoniometry on a sub group (navigated=60, conventional=57) at 12 months post surgery.

The EM group showed statistically significantly improved OKS (p=0.04) and AKSS (p=0.03) scores at 3 months post operation. However at 12 months post surgery there was no difference between the two groups. At the 1 year follow up it was reported that 9% of the navigated compared to 14% of the conventional group were dissatisfied with their surgical outcome.

The mechanical axis alignment of 90% of the navigated group was within 3 degrees of neutral compared to 84% of the conventional group. Although all alignment parameters except for tibial rotation was improved in the navigated group they did not reach significance apart from femoral slope alignment (p=0.01).

There was no statistically difference between the surgical groups in terms of the maximum, minimum and excursion knee joint angles during 12 functional activities. Only the knee kinematic function cycles for level walking resulted in statistically significant higher knee joint angles during 55–70% of the gait cycle in the navigated group.

Knee alignment was better restored following EM navigated TKA relative to conventional TKA, but the difference was not significant. The EM group showed greater clinical and functional improvements at early follow-up; however this difference was not sustained at 12 months. The EM group reported minimal gait improvements. Proving cost-effectiveness for navigation systems in TKA remains a challenge.

The aim of this study was to determine the influence of electromagnetic (EM) navigation in total knee arthroplasty (TKA) on post operative function.

In this double blinded randomised control trial, patients with osteoarthritis either received TKA using conventional techniques (n = 49) or EM navigation (iNav Portable Navigation System, Zimmer Orthopaedics) (n = 52). All of the patients were reviewed in the Outcomes Clinic at 3 and 12 months. At 12 months post operation the patients completed an objective biomechanical functional assessment using flexible electrogoniometers, which recorded dynamic knee kinematics during daily activities. Knee joint flexion and extension moments were recorded at the 12 month post operation assessment. The functional assessment included validated questionnaires (Oxford Knee Score, American Knee Society Score, WOMAC Score and Short Form SF-36 Score). All patients underwent CT scanning of the implanted prosthesis to assess component alignment.

Improved alignment was recorded in the navigated group. However there was no significantly significant difference between the two surgical groups in terms of the subjective questionnaire scores. The biomechanical assessment showed no statistically significant differences in the maximum, minimum or excursion knee joint angles between the two surgical groups during the 12 daily functional tasks. However, significant differences were reported in level and slope walking activities during pre-swing phase (at around 60% of the gait cycle). The navigated group had significantly higher knee joint angles during pre swing suggesting a more vigorous push off into swing phase and a more ‘normal’ gait cycle. The two surgical groups were sub divided into males and females for the strength test. The female navigated group recorded a significantly greater hamstring (p = 0.03) and quadriceps (p = 0.003) moment. There was no significant difference in hamstring or quadriceps moments between the navigated and conventional male groups.

The knee kinematics and moment data suggests that the navigated group had an improved functional outcome. However the difference in the post-operation function of the two groups remains minimal despite the better alignment achieved using navigation.

There is increasing interest in the use of image free computer assisted surgery (CAS) in total hip arthroplasty (THA). Many of these systems require the registration of the Anterior Pelvic Plane (APP) via the bony landmarks of the anterior superior iliac spines (ASIS) and pubic tubercles (PT) in order to accurately orient the acetabular cup in terms of anteversion and inclination. Given system accuracies are within 1mm and 1° and clinical validation studies have given accuracy by cup position. However, clinical outcomes contain not only system inaccuracies but also variations due to clinical practice. To understand the effects of variation in landmark acquisition on the identification of the acetabular cup orientation, independent bench testing is required. This requires a phantom model that can represent the range of pelvises, male and female, encountered during THA and introduce deliberate known errors to the acquisition to see the effect on anteversion and inclination angles. However, there is a paucity of information in the literature with regards to these specific pelvic dimensions (pelvic width and height). Therefore the aims of this work were to generate the normal expected range of sizes of the APP for both males and females and to use these to manufacture a phantom model that could be used to assess CT free navigation systems.

In the first part of the study 35 human cadavers and 100 pelvic computed tomography (CT) scans were examined.

All cadavers had no gross pelvic abnormalities or previous surgeries. Measurements were carried out with cadavers placed in a supine position. The first author made three sets of measurements using a millimeter ruler. Solid steel pins were used to identify the palpated ASISs and PTs. String was tied between the two ASIS pins and the pelvic width measured. The midpoint of the pubic tubercles was taken to be the midpoint of the pubic symphysis. Pelvic height was measured from the midpoint of the ASIS distance (marked on the string) to the midpoint of the PTs. One hundred pelvic CT scans with no bony abnormalities, previous surgery or metal prosthesis (due to artefacts) were obtained retrospectively from the hospital radiological online system (PACS, Kodak). Mimics software (Mimics12 Materialise, Leuven, Belgium) was used to automatically reconstruct three-dimensional (3D) models using the ‘Bone’ thresholding function. This eliminated any soft tissue from the 3D models. The most anterior ASIS and PT points were then identified on the 3D model surface and measurements of distances made. As the software did not allow identification of points not on the model surface it was not possible to directly obtain the midpoint of the ASIS distance. Therefore to obtain the pelvic height measurements the distance between each ASIS and the ipsilateral and contralateral PTs was also measured. The pelvic height was then calculated using trigonometric functions. The ratio of width to height was calculated (ratio > 1 indicating pelvis width greater than pelvis height). Student's t test was used analyse any differences between male and female pelvic measurements with a p<0.05 being statistically significant.

Using the results from above an aluminium pelvic phantom model was designed and manufactured. It was machined from a billet of marine grade aluminium alloy using a vertical computer numerical controlled (CNC) milling machine. The top surface represented the APP and sides (which represented the acetabuli) were angled to give anteversion and inclination angles of 20° and 45° respectively. Co-ordinates for ASIS and PT points were given based on the 99% prediction intervals from the pelvic data and additional points were milled to give up to a 20 mm error mediolaterally and also in height. Each co-ordinate point was drilled with a 2.0mm diameter ball-nose cutter to a depth of 1.0mm, these holes designed to accommodate the ball-nosed pointer tip to ensure it remained at the same position in space at all orientations of the pointer. Further to this, known errors in height were introduced using accurately manufactured blocks with similar points milled on the surface to fit a ball-nosed pointer. These blocks could be secured to the top surface of the model using screws. A Perspex base unit with tracker attachments was made to hold the phantom and provide the reference frame. A further support that enables the phantom to also be used in the “lateral” position was manufactured.

For the assessment of pelvic size there were 66 females and 69 males, mean age 62.3 years (range from 20 to 99 years). The mean width was 238 mm (SD 20 mm) and mean height was 93 mm (SD 11 mm) with a mean ratio of 2.6 (SD 0.3). There were no statistically significant differences in mean between males and females (p>0.4 in all cases). From this data set the range of APP sizes required to cover 99% of population (width 186 to 290 mm and height 66 to 120 mm) and therefore the measurements for the model were generated. The manufactured model can be used to give the range of pelvis sizes from 170mm to 290mm in width and 60mm to 120mm in height and also to add up to 20 mm of error in palpation of each of the ASISs and PT.

This study generated APP sizes to cover 99% of the general population over a wide age range. It illustrated that a single pelvic model would fit both sexes. The model allows the determination of the effects of changes of the pelvic dimensions may have on the acetabular orientation measured on an image free CAS system including the assessment of point acquisition and deliberate errors. The model has been successfully used in preliminary testing and can be used to assess any CT free system.

Computer assisted surgery is becoming more frequently used in the medical world. Navigation of surgical instruments and implants plays an important role in this surgery. OrthoPilot™ Hip Suite (BBraun Aesculap) is one such system used for hip navigation in orthopaedic surgery. However the accuracy of this system remains to be determined independently of the manufacturer. The manufacturer supplies a technical specification for the accuracy of the system (± 2 mm and ± 2°) and previous research has been undertaken to compare its clinical accuracy against conventional hip replacements by x-ray. This clinical validation is important but contains many sources of error or deviation from an ideal outcome in terms of the surgeons' use of the system, inaccurate palpation of landmarks, variation in actual cup position from that given by the navigation system and measurement of the final cup position. It is therefore not possible to validate the claims of the manufacturer from this data. There is no literature evaluating the technical accuracy of the software i.e. the accuracy of the system given known inputs. This study had two main aims 1) validating the accuracy of the OrthoPilot data while navigating the surgical instruments and 2) validating the accuracy of navigation algorithm inside the OrthoPilot system which determines cup implant placement. The OrthoPilot validation was performed and compared against the gold standard of a VICON movement analysis system.

The system used was OrthoPilot™ with a Spectra camera from Northern Digital Inc. (Ontario, Canada). Software investigated was the Hip Suite THA cup only navigation software Version 3.1. The validation was performed and compared against the VICON Nexus version 1.4.116 with Bodybuilder software version 3.55. An aluminium pelvis phantom was used for measurement allowing accurate and repeatable inputs. The OrthoPilot system has three types of instruments sets; passive, active and hybrid. This study was carried out with the passive instruments set. Data were captured simultaneously from both the OrthoPilot and VICON systems for the supine position of the phantom. Distances between the anatomical land marks on the phantom were compared to test the data capturing accuracy of the OrthoPilot system. Anatomical land marks of right anterior superior iliac supine (RASIS), left anterior superior iliac supine (LASIS) and Pubic Symphasis (PS) were palpated to define the Anterior Pelvic Plane (APP). Distances between the anatomical landmarks of RASIS to LASIS, RASIS to PS and LASIS to PS were considered for comparison. Width and height of the pelvis was varied to examine different APPs. The width and height used were 170 mm and 53 mm, 230 mm and 88 mm, and 290 mm and 123 mm respectively. One hundred APP data sets were captured at each instance.

The accuracy of the hip navigation algorithm was tested by applying similar algorithm to calculate the native anteversion and inclination angles of the acetabulum using the VICON system. Data were captured simultaneously from both OrthoPilot and VICON systems. Radiographic anteversion and inclination angles were obtained with phantom model, which had 14° of anteversion angle and 45° of inclination angle. APP of 230 mm in width and 88 mm in height was used to obtain anterior pelvic plane data. Position vectors for each anatomical land mark from the OrthoPilot system were extracted from relevant transformation matrices, while position vectors from the VICON system were extracted from static trial modelling.

The distance data from both systems were compared with calibrated distance data from the phantom model. Mean values of the distances between anatomical landmarks were found to be similar for both OrthoPilot and VICON systems. In addition, these distances were comparable with the pelvic phantom model data, within 1 mm for all measured distances for the VICON and 2 mm for the OrthoPilot. Furthermore, the standard deviations were less than 1% of the measured value. Comparison was also made for the anteversion and inclination angles of the acetabulum of the pelvic model with OrthoPilot and VICON data. Both systems produced similar results for the mean angle values, within 0.5° of the known angles for the VICON and 1° for the OrthoPilot and with standard deviations of the measured values of less than 1%.

All the data were captured simultaneously from both OrthoPilot and VICON systems under the same laboratory conditions. According to the above results it is clear that the distance readings obtained from the OrthoPilot are comparable to the results obtained from the gold standard VICON system and the calibrated distance readings of the phantom. In addition, acetabular angle results obtained from OrthoPilot are almost equivalent to results obtained from VICON and the calibrated phantom angles. Finally it is can be concluded that, both the data palpation with OrthoPilot system and acetabular angle calculation algorithm of the OrthoPilot system are accurate enough for the real world clinical tasks they are expected to perform.

Electromagnetic navigation versus conventional Total Knee Arthroplasty: Clinical improvements Optical and electromagnetic (EM) tracking systems are widely used commercially. However in orthopaedic applications optical systems dominate the market. Optical systems suffer from deficiencies due to line of sight. EM trackers are smaller but are affected by metal. The accuracy of the two tracker systems has been seen to be comparable1. Recent advancements in optical navigated TKA have shown improved overall limb alignment, implant placement and reduce outliers when compared to conventional TKA2-4.

This study is the first RCT to compare EM and conventional TKA. Two groups of 100 patients underwent TKA using either the EM navigation system or the conventional method. Frontal, sagittal and rotational alignment was analysed from a CT scan. Clinical scores including Oxford Knee Score (OKS) and Knee/Function American Knee Society Score (AKSS) were recorded pre-op, and at 3 and 12 months post-op. 3 month data presented includes 180 patients (n = 90). The 12 months data presented includes 140 (n = 70).

The two groups had similar mean mechanical axis alignments (EM 0.31o valgus, conventional 0.15o valgus). The mechanical axis alignment was improved in the EM group with 92% within +/-3o of neutral compared to 84% of the conventional group (p = 0.90). The alignment of the EM group was improved in terms of frontal femoral, frontal tibial, sagittal femoral, sagittal tibial and tibial rotation alignment. However, only the sagittal femoral alignment was significantly improved in the EM group (p = 0.04). Clinically, both TKA groups showed significant improvements in OKS and AKSS scores between both pre-op to 3 month post-op and 3 months to 12 months post-op (p<0.001). The OKS and the AKSS knee score for the EM group was significantly better at 3 months post-op (OXS p = 0.02, AKSS knee p = 0.04). However there was no difference between the groups at 12 months. The mean pre-op range of motion (ROM) for both groups was 105o. This decreased to 102o in the EM group and 99o in the conventional group at 3 months. There was a significant improvement at 12 months post-op, EM = 113o (p = 0.012) and conventional = 112o (p = 0.026). There was no significant difference in ROM between the two groups at 3 or 12 months post-op.

Therefore the alignment outcome of the EM TKA group was improved compared to the conventional group. The EM group also showed clinical improvements at 3 months post-op however these were not seen again at 12 months post-op. ROM was seen to decrease at 3 months post-op but then significantly improve by 12 month post-op.

Recent advancements in optical navigated TKA have shown improved overall limb alignment, implant placement and reduced outliers compared to conventional TKA. This study represents the first RCT comparing EM navigation and conventional TKA. 3D alignment was analysed from CT scans. Clinical scores (Oxford Knee Score (OKS) and American Knee Society Score (AKSS)) were recorded at pre-op, 3 and 12 months post-op. Data presented includes 180 patients (n=90 per group) at 3 months and 140 (n=70 per group) at 12 months.

The groups had similar mean mechanical axis alignments (EM 0.31° valgus; conventional 0.15° valgus). Mechanical axis alignment however was improved in the EM group with 92% within +/−3° of neutral compared to 84% of the conventional group (p=0.90). The EM group showed improved coronal and sagittal femoral alignment and improved coronal, sagittal and rotational tibial alignment, which was significant for sagittal femoral alignment (p=0.04). The OKS and AKSS scores were significantly better for the EM group at 3 months post-op (OKS p=0.02, AKSS p=0.04), but there was no difference between groups at 12 months. The mean pre-op range of motion (ROM) for both groups was 105°. This decreased at 3 months to 102° in the EM group and 99° in the conventional group, but there was a significant improvement by 12 months: EM=113° (p=0.012) and conventional=112° (p=0.026). ROM was statistically similar between groups at all assessment phases.

Knee alignment was better restored following EM navigated TKA relative to conventional TKA, but the difference was not significant. The EM group showed greater clinical improvements at early follow-up; however this difference was not sustained at 12 months. ROM was seen to decrease at 3 months but then significantly improve by 12 month post-op. Proving cost-effectiveness for navigation systems in TKA remains a challenge.

The aim of this study was to investigate the pre-operative factors predicting the knee range of motion during stair ascending and descending a year after total knee arthroplasty.

The pre-operative and one year post-operative results of fifty six patients with osteoarthritis were analysed. Range of knee motion during stair ascent and descent was recorded using electrogoniometry. Pre-operative measures were grouped in three different domains; the Demographic Domain with age and Body Mass Index (BMI), the Body Function Domain with knee range of motion in long sitting (ROMsit), Knee extensor moment, Pain on a Visual Analogue Scale and the stiffness component of the Western Ontario McMaster University Osteoarthritis Index (WOMAC) and thirdly the Psychosocial Domain with the Tampa scale for ‘fear of movement’ (TSK) and the sense of helplessness due to pain. Hierarchical Multiple Regression was used to analyse the relative importance of measures grouped into the three domain blocks on range of motion of the operated knee during stair ascent and descent. Model 1 contained domain block 1, model 2 included domain blocks 1 and 2 and model 3 included domain blocks 1,2 and 3.

Learned helplessness was a significant predicting factor for stair descent (beta; −0.538, p=0.025) while for stair ascent, age (beta 0.375, p=0.005) and ROMsit (beta 0.365, p=0.021) were significant predicting variables.

These results show that postoperative stair ascent and descent are predicted by different pre-operative factors. For stair ascent the demographic factors age and function factor ROM are important, while for stair descent, only the addition of the psychosocial factors in model 3 resulted in a significant change. These results indicate that treatment of patients with end-stage osteoarthritis should not only be aimed at improving range of motion of the knee but should also take into account psychosocial variables such as a sense of helplessness due to pain.

The primary aim of this study was to investigate whether objective daily physical activity, measured using an activity monitor one year after Total Knee Arthroplasty was different from that measured before surgery.

An activity monitor (activPAL) which records the number of steps in addition to the time spent sitting or lying, standing and ‘stepping’ was used to quantify physical activity. Forty-five patients with osteoarthritis (average 69.8 years old) were assessed an average of 38 days before and 368 days after total knee arthroplasty-before. A group of 40 age matched controls were also recruited. In addition to objective daily physical activity, knee range of motion, pain using the visual analogue score and the Western Ontario McMaster University Osteoarthritis Index (WOMAC 3.1) were also recorded before and after surgery.

Patients reported a significant decrease in pain (54%, p< 0.001) and increase in function (62% p< 0.001) after surgery. However, measures of physical activity showed much smaller improvements which were mostly statistically non-significant. The number of steps taken on one day increased by 19% (from 6438 to 7634 steps, p=0.119) and time spent stepping increased from 7.9% to 8.7% (p=0.27). Only average cadence and estimated energy expenditure were statistically significantly higher after surgery, 8% improvement, p=0.003 and 8% improvement, p=0.026 respectively. Stepwise regression analysis showed that only 11.4% of the improvement in physical activity was due to the decrease in pain.

One year after TKA levels of physical activity were still significantly (p< 0.05) lower than those of a group of age matched controls. In conclusion, other factors not measured in this study are to a large part determining the amount of physical activity in patients after knee surgery. Future studies aiming to identify those factors are warranted.

The aim of this study was to investigate the effects of implant design and gender on the outcome of Total Knee Arthroplasty (TKA) in patients with osteoarthritis (OA).

In this double blind randomised controlled trial, patients with OA received either a standard posterior stabilised implant (n=28) or high flex version of this implant (n=28). Walking speed, knee flexion under anaesthesia (‘drop test’), knee flexion in sitting and during functional activities as measured by electrogoniometry, daily number of steps, Quality of Life (SF36), the function component of the Knee Society Score, pain (Visual Analogue Score) and extensor strength were measured before and one year after TKA.

Type of implant did not have a significant effect on any of the outcome measures recorded, while gender showed significant effects both before and after surgery. Before surgery, females had a significantly lower knee range of motion, (both passive and functional), lower Knee Score function component, walking speed and strength. After surgery they had a statistically significant lower range of knee motion during functional activities such as walking up and down a slope. Strength was also still significantly lower but post-operative self-reported function were similar for both genders. There was also no difference between male and female participants regarding Quality of life, objective daily physical activity or pain.

The results of this study showed that there is a clinically and statistically significant difference between the function of female and male patients both before and after total knee arthroplasty. Although female patients seem to benefit more from TKA than males, on average they do not achieve the same functional knee motion after surgery. Unlike gender, implant design did not influence the knee motion or function in this group of patients. This has important implications for future research and treatment planning in order to maximise the functional outcome after TKA.