Bio tribology of the patella femoral joint in total knee replacement

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.