(7) How are artificial hip replacements tested prior to being made available for clinical use?

New or modified hip replacements will undergo a number of tests that have been agreed within international and national bodies. These tests will test for the overall levels of wear using a pre-agreed protocol such that the wear from different prostheses can be compared. Other tests investigate the fatigue strength of the stem or the reaction to polymeric wear debris. Further, the range of materials are limited for reasons of toxicity and function. These materials are tightly specified such that their variability in mechanical properties is quite narrow. Once a body of evidence has been accrued that would suggest that the device is safe for use then a submission may be made to a regulatory authority to allow the implant to be used clinically and/or undergo a clinical trial. An issue highlighted around the current crop of poor-performing metal-on-metal total hip and resurfacing replacements has been the fact that none of the these standard tests appeared to highlight the potential for relatively high levels of wear and the possible high risk of failure. One reason for the lack of testing evidence was that the wear becomes problematic when adverse joints mechanics occur (e.g. when the femoral head is in contact with the socket edge) and that the testing regimes are largely focused on normal, and not adverse, activities.

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