Comparative in vitro wear testing of PEEK and UHMWPE capped metacarpophalangeal prostheses

Six metacarpophalangeal prostheses were each wear tested to five million cycles. Each prosthesis consisted of a metacarpal component with an approximately hemispherical shell on a titanium body, articulating against a titanium phalangeal component. Four prostheses had a shell made from ultra-high molecular weight polyethylene (UHMWPE) and two had a shell made from polyether ether ketone (PEEK). The tests were undertaken using a finger wear simulator. Despite pre-soaking and the use of control components, lubricant uptake by the metacarpal components was significant. Gravimetrically, the UHMWPE test components showed a greater weight gain than the UHMWPE control components. Therefore there was no apparent wear of any of the UHMWPE test metacarpal components. The original concentric machining marks of the UHMWPE components could still be seen after five million cycles of testing. For the metacarpal components with PEEK shells, gravimetric wear could be measured. Gravimetrically, all of the titanium phalangeal components showed little or no wear. Light scratches in the direction of sliding appeared on the articulating faces of all metacarpal and phalangeal test components, indicating slight abrasive wear.