Total knee replacements: design and pre-clinical testing methods

Abstract

Total knee replacement (TKR) is a common and successful treatment for severe osteoarthritis of the knee. However, a large minority of people remain dissatisfied after the operation, despite adequate pain relief. Over 50 designs of TKR are used in the UK each year, but differentiating between these devices in terms of patient function and making the right choice for each patient remains challenging. The aim of this research was to characterise designs of TKR in the laboratory, using pre-clinical testing methods, in order to better understand TKR function, and make suggestions for improved implant design and testing. Conventional, medial-pivot, guided-motion and bicruciate retaining (BCR) TKRs were tested. Standard ASTM test methods used for CE-marking purposes were demonstrated to differentiate between devices, but did not produce enough information to adequately understand how a new device will behave clinically, or what the potential benefits of a new device would be to patients. Guided-motion devices are meant to replicate normal knee motion, but there has been concern that they might cause too much rotation of the knee, leading to anterolateral knee pain. Results from cadaveric testing suggest that they do not adequately mimic normal knee motion and small design changes may have little impact on performance. A BCR TKR, designed to improve stability in the replaced knee joint, was also tested. Knee kinematics were measured for three design phases and surgical feasibility was also assessed for this more complicated procedure. BCR TKR was shown to lead to more normal levels of anteroposterior tibiofemoral laxity, compared to a conventional, anterior-cruciate-ligament-sacrificing TKR. Inherent variability between people’s anatomy and osteoarthritis pathology suggests there will never be a single, perfect, TKR, but more comprehensive pre-clinical testing could improve the regulatory approval process and inform better device selection, leading to improved patient outcomes.