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Posterior stabilised total knee replacements incorporate a cam/post mechanism which is intended to increase posterior translation of the femur on the tibia in flexion. A review of the literature revealed that there were different opinions as to the effectiveness of posterior stabilised total knee replacement designs in improving kinematics. The aims of this thesis were to investigate why current posterior sta- bilised total knee replacement designs do not improve kinematics, and how cam/post design could be modified to improve posterior translation in flexion. A set of measurement tools to determine cam/post engagement, tibio-femoral kinematics and patello-femoral kinematics were designed, developed, and validated. These tools were assessed for accuracy using computer simulation and in vitro meth- ods. The tools were used to investigate the sagittal plane knee kinematics of a group of patients implanted with posterior stabilised knee replacement (Scorpio PS) and compare this data with the kinematics of normal knees. The cam/post mechanism was found to engage and to have a positive influence on the kinematic profile. How- ever, the kinematics of the Scorpio posterior stabilised design differed from those of the normal knee. A two-dimensional sagittal plane patient specific model of the knee was devel- oped. The model, driven by the knee flexion angle, was capable of predicting the patella tendon angle of implanted knees for a given relative tibio-femoral relation- ship. The model was validated against the in vivo data collected for the group of knees implanted with the Scorpio posterior stabilised implant. The model was then used to assess an existing knee design, the Vanguard, and compare the predictions to the data for normal knees. The Vanguard was found to have abnormal kinematics. The model was then used to optimise the design to achieve more normal kinematics. The modified design incorporated an improved cam/post mechanism and a reduction in articular surface constraint. To validate the new optimised design, a prototype was manufactured and tested using in vitro methods. The experiments showed the cam/post mechanism of the modified implant was more effective in improving the kinematic profile in flexion.

The use of, and interest in, total knee replacements (TKR) has been growing over the last few decades. Loosening and migration of tibial components have been identified as one of the primary causes of failure in the proximal tibia. Clinical studies show the use of metal implants as one of the primary methods for the treatment of knee joints and associated bone defects. Alignment and fixation techniques play an important role in achieving high success rates. Defective bone stock requires the use of augments to stabilise the tibial plate. In these cases, current clinical practice is to use an extended implant stem to ensure stability. The problem with this is that it reduces the potential for future knee revision In this research Finite Element Analysis (FEA) has been used to undertake virtual in-vivo assessment of various configurations of augmented and non-augmented TKR that can be used for the treatment of tibial defects. These configurations are based on a standard tibial insert, namely a fIxed bearing revision tibial tray. This has provided insight and information that can be used to improve surgical decision making when dealing with defective bone stock. The 3D FE models of a non-defect TKR with a fixed bearing tibial insert showed a stable construct with stresses lying within an allowable threshold. The use of a stem extension generally showed a reduction in stress levels in the cancellous bone contributing to an increase in stress shielding and thus it is recommended that these are not used unless there is some other overriding clinical requirement. Further, the analysis demonstrated that, contrary to some clinical opinion, wedge augmentation (rather than block augmentation) may provide a better approach to treat the defect. This was largely due to improved cement stress distribution caused by a mechanism termed "reverse-shear". The use of a cement augment was found to provide a more favourable stress distribution in the cancellous bone. However, metal augments have been recommended as the cement augment was shown to operate too close to its fatigue endurance limits. Future work should focus on further enhancements of the bio-fidelity of the FE model particularly in the material distribution. The idealisation of the cancellous bone as a uniform isotropic material can be improved to provide a spatially varying distribution of material properties, reflecting the natural variation in bone density. Another aspect to further enhance this work would be to extend the applied loads to reflect other lower body movements and to consider the effect of friction at the condyles on the anterior-posterior load applied.

Due to the fact that a growing number of young patients require joint replacements, the expected lifetime of the prostheses is considerably increasing, and patient activities are becoming more demanding. New materials and designs are being introduced. The technical challenge lies in developing new designs, with high-performance materials, and low wear to improve prosthesis life. The main issue is to pre-clinically investigate the new materials and designs. Many researchers have reported wear in total knee replacements investigated in simulators. A single simulator test can be very expensive and take a long time to run. Computational wear modelling is an alternative attractive solution to these limitations, particularly when combined with experimental studies to provide input as well as validation. However, historical computational wear models have adopted the classical Archard's wear law, which was developed for metallic materials, and have selected wear factors arbitrarily from literature. It is known that such an approach is not generally true for polymeric bearing materials and is difficult to implement due to the dependence of wear factors on contact pressure as well as cross-shear. Therefore, these studies are generally not independent and lack general predictability. The objective of the present study was to develop a new computational wear model for the knee implants, where the wear volume dependent on sliding distance and contact area, based on an independent experimentally determined non-dimensional wear coefficient. The effects of cross-shear and creep on wear predictions were also considered. Independent experimental pin-on-plate multi- directional wear tests were conducted to provide the required input parameters. The output results from the new computational model were compared with the data from the experimental knee simulation tests in Leeds and parametric studies for different designs, materials and different operating conditions were conducted. The results suggested that the computational wear modelling, based on the new wear law and the independent -experimentally calculated non-dimensional wear coefficient, were more reliable, and therefore provide a more robust virtual modelling platform. In addition, the results showed that potential methods for increasing the expected total knee replacement lifetime might be to introduce less conforming knee replacement and to use cross-linked polyethylene as a bearing material.

Current techniques used for total knee arthroplasty (TKA) rely on conventional instrumentation (CI) systems that violate the intramedullary canals. The accuracy of these systems is questionable, and set up and assembly of their numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. The aim of this study was to prove a new concept of computer assisted preoperative planning to provide patient-specific templates (PST) that can replace conventional instruments. Computed tomography based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. Forty five TKA procedures were performed on 16 cadaveric and 29 plastic knees using the PST technique. Six out of 29 TKA procedures were included in a comparative trial against 6 procedures performed using CI systems. Computer assisted analysis of 6 random postoperative CT scans was performed to evaluate the accuracy of this technique. A reliability test was performed, in which five observers positioned the templates on a plastic knee model and a navigation system was used to measure alignment and the level of bone cutting for the planned tibial and femoral cuts. Each observer repeated the test 5 times. Errors in placement of the templates as well as intraobserver and interobserver variations were measured. The study showed that it was possible to perform all 45 TKA procedures without CI systems. There was no need for intramedullary perforation, tracking or registration. The mean time for bone cutting was 9 minutes (15 minutes for CI systems), when the surgeon had an assistant and 11 minutes (30 minutes for CI systems), when the surgeon was unassisted. Postoperative CT scans showed mean errors of 1.70 and 0.8 mm (maximum 2.30 and 1.2 mm) for alignment and bone resection respectively. The reliability test had a mean alignment error of 0.670(maximum 2.50). The mean error for bone resection was 0.32 mm (maximum 1 mm). The positioning of the templates was reliable, as there was no significant intraobserver and interobserver variation. This study proved the concept of patient-specific templating for TKA. It also showed a satisfactory level of accuracy and reliability of this technique. In conclusion, the PST technique has several advantages over conventional instrumentation and it is a simple alternative to navigation and robotic techniques for TKA. Further clinical validation is required before recommending this technique for new users.

Total knee replacement remains the final treatment for patients suffering from knee arthritis and providing relief from pain and improvement in function. Despite the fact that the common reason for revisions of TKR is due to problems regarding patella femoral joint, the use of patella during TKA varies from country to country with popularity in USA (90%), Denmark (76%), Australia (43%), England and Wales (33%), Sweden (14%) and Norway (11%). Research was performed into the in vitro wear simulation of the patella femoral joint but to date none of these simulations have employed all six degrees of freedom. The aim of this study was to • develop a six axis patella femoral joint simulator for assessment of wear, •develop a computational model to predict the kinematics of the patella femoral joint and validate using experimental knee joint simulator results, • investigate the influence of kinematic parameters (patella rotation, displacement and tilt) and shape (round and oval dome patella) on the wear of the patella femoral joint, • validate and develop other volumetric measurement techniques, • validate the experimental wear results with the retrievals volumetric analysis. The six station Leeds Prosim knee simulator was modified as a patella femoral knee simulator for the wear assessment process. Good overall agreement between the computational prediction and the experimental measurement were obtained for patella femoral kinematics. Increasing the medial lateral rotation significantly increased the wear rate from 8.6 mm3/MC to 12.3 mm3/MC. Decreasing the medial lateral displacement led to a no significant change in the wear rate. Changing the shape from round dome to oval dome led to a non significant decrease in wear rate from 8.7 mm3/MC to 6.3 mm3/MC. Ten retrievals were analyzed for volumetric and surface wear. Wear volume per year for retrievals were obtained in range of 0.9 mm3/year to 18.7 mm3/year. The wear scar area was similar in shape with the in vitro analysis validating the wear analysis.

Aims: To determine the effects of tibial component rotation and posterior slope on kinematics following Scorpio CR navigated TKR in cadaver specimens. Methods & Results: Knee kinematics were monitored using a validated IR Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads. Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. Combined malrotations over 10 degrees with posterior slopes over 6 degrees resulted in prosthetic subluxation under certain loading conditions. Discussion: Knee kinematics are different after TKR. Increasing internal and external malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics, and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Interpositional arthroplasty is a treatment option for isolated medial compartment osteoarthritis of the knee. No bone resection and no mechanical fixation are the main advantages of this procedure. However post-operative problems, such as implant dislocation, swelling and severe knee pain have been generally observed. Since these problems are related to the motions and loads occurring at the knee and probably to design factors of the implant, there is a need to investigate the kinematics and contact mechanics of the knee implanted with an interpositional spacer and its differences with respect to the normal knee. Although the knee joint is routinely involved in dynamic activities, to date, no experimental or numerical studies have investigated the kinematics and contact mechanics of the normal knee joint during dynamic loading conditions, most of the experimental and finite element studies are static or quasi-static in nature. Hence the purpose of this study was to investigate: 1) the behaviour of the normal knee joint under dynamic loading conditions, 2) the performance of a knee implanted with an interpositional spacer and 3) the effect of several implant design parameters on the behaviour of the implanted knee. The kinematics and contact pressures of the normal knee joint during the activities of walking, stair ascent and squatting were obtained using dynamic finite element analysis. Higher contact pressures were predicted when applying more demanding loads, during the simulation of the squatting and stair ascent activities. Similar ranges of motion were predicted for the three activities simulated, despite the difference in the magnitude of the loads applied, due to the restraining function of the ligaments and the geometry of the surfaces into contact. In the second study, the kinematics and contact pressures of a knee implanted with a polyurethane interpositional spacer were obtained and compared to the normal knee. In general, for the three activities simulated, the implanted knee was able to follow the kinematics of the normal knee, however higher contact pressures were predicted in the medial side of the tibial and femoral articular cartilages, which could increase the propensity for articular cartilage degeneration. In the third study, the influence of implant material, size, thickness and radii of the bearing surface in anterior/posterior and medial/lateral directions was assessed. A hard material compared to the menisci, such as a cobalt-chromium alloy, caused higher contact pressures in both the medial and lateral side of the knee. Implant size did not affect the kinematics or contact pressures in the knee, however anterior dislocation of the implant was observed for a large spacer during the squatting activity. Thickness and radii of the bearing surface did not show any significant influence on the kinematics or contact pressures.

Total joint replacement is one of the most common elective surgical procedures performed worldwide, with an estimate of 1.5 million operations performed annually. It has long been recognised that wear analysis of total joint replacements is an important means in determining failure mechanisms, functionality and improving longevity of these devices. The standardised method for assessing wear volumes in such joints is through gravimetric means and it has been shown that this method is a useful tool for indicating simulated wear volumes. This method is, however, of little value when considering the case of a clinically explanted bearing surface for which, by definition, there is no ‘pre-wear’ data. The purpose of this thesis is to present a co-ordinate measuring machine (CMM) based technique for assessing the volumetric material loss in total joint replacement joints and to establish its effectiveness. To this end uncertainty calculations are completed for the specific case of orthopaedic component measurement. In this thesis methods have been developed in this thesis for measurement of in vitro wear of total knee replacement bearings and a number of knee joint simulator tests have been completed and their results discussed. An initial test investigating the possible use of metal-on-metal bearings for total knee replacement is described. A test profile for simulation of deep squat is developed, a simulator test completed and the results discussed. An adapted version of the developed CMM measurement method is further adapted and developed for measurement of clinical wear from retrieved bearings and the implications of this capability are examined and discussed. In tandem with this methods are developed for the mapping of wear location and component form deviation and the implications that this has for manufacturing control and wear potential is discussed at length. Overall future developments and work are explored.