Tribological Assessment of UHMWPE in the Knee

The testing of implants can be generally categorized into in vivo and in vitro testing. This chapter deals with in vitro tests. The obvious main benefit of such tests is that the evaluation can be made at the total knee replacement (TKR) design and prototyping stage and thus can not only screen risks prior to clinical use but can aid with useful feedback to the design process. TKR is quickly approaching and virtually all current TKR designs use ultra-high molecular weight polyethylene (UHMWPE) as a bearing component. With rising demand for TKR from a significant part of the aging population, more manufacturers and more types of prostheses continue to emerge, and the number of surgeons who carry out TKR and revision operations is probably increasing fastest of all. The testing of such a variety of implants poses a challenge. Testing itself needs to be standardized to help the industrial design process and to help the regulatory bodies in the screening of implants prior to their use clinically. The tribological testing of UHMWPE destined for TKR started with pin-on-disk (POD) testing, where preliminary screening of materials is needed. POD testing was described and could not take any consideration of the TKR design in the planning of the test, except for choices of articular contact area of the pin and the stress levels through suitable choices of loading. © 2009