WEAR AND DAMAGE CHARACTERISTICS OF THE UPPER AND LOWER SURFACES OF THE BEARINGS IN A LOCALLY DESIGNED MENISCAL KNEE PROSTHESIS.

Abstract

Meniscal knee designs are unlike conventional surface replacement designs as they have two moving surfaces between the polyethylene and the metal tibial tray. This means the sliding distance is shared over two surfaces. This study was performed to assess the damage to both surfaces and whether the concept of wear sharing exists in knee prostheses of these designs.

Although 22 meniscal bearings from both the designs of knee prosthesis of the Minns design were collected, 4 pairs of bearings (2 from each design of the Minns knee) were examined in detail as it was felt they represented the range of damage features seen in the explanted samples. These samples were examined for wear and damage on both the upper and lower polyethylene surfaces. In both designs of bearings, the wear was significantly less extensive on all the lower surfaces examined. The roughness of the burnished areas on the upper surface was always less than any of the lower surfaces of the same bearing. Even the specimens with gross wear and delamination damage on the upper surface has no corresponding damage on the lower surface. Only one specimen had wear on the lower surface of the dovetail retention bar, usually no wear was seen on this surface indicating the main weight-bearing area is the lower flat surface of both designs of bearings, and that the sliding distance is shared during use thus reducing the wear factor for both surfaces in use.