AN ANALYSIS OF HYLAMER AND POLYETHYLENE BEARINGS FROM RETRIEVED ACETABULAR COMPONENTS

Hylamer and conventional polyethylene acetabular liners of the same de sign, revised for a variety of reasons, were examined and compared to assess the performance of Hylamer as a bearing material. Clinical dama ge modes, linear wear rates, oxidation levels, and mechanical properti es were measured. In both series, many liners were retrieved for dislo cation. Wear/osteolysis was the most common reason for retrieval in th e Hylamer series, while none of the conventional polyethylene liners w ere retrieved for this reason. Nearly all liners exhibited abrasion, b urnishing, scratching, and creep. The Hylamer liners had more cracking , delamination, and pitting. The Hylamer liners had an average linear wear rate of 0.32 mm/year, while the conventional polyethylene liners had an average wear rate of 0.20 mm/year. Due to sample size, no stati stical difference in wear rate was noted between the two groups. In ge neral, both the Hylamer and conventional polyethylene showed oxidation peaks subsurface, resulting from their exposure to gamma radiation in air. Liners with elevated oxidation had decreased ultimate tensile st rength, elongation, and toughness. For given oxidation levels, the cor responding mechanical properties of Hylamer appeared lower than those of conventional polyethylene. The ultimate tensile strength values ran ged from 14 to 33 MPa for Hylamer and 19 to 32 NPa for conventional po lyethylene. Elongation ranges were 19% to 350% (Hylamer) and 80% to 37 5% (conventional). The Hylamer retrievals in this study gave initial i ndications of performance; Hylamer appeared to behave similarly, but n ot superiorly, to conventional polyethylene, in the early functional p eriod with respect to clinical wear and clinical performance. Both Hyl amer and conventional polyethylene liners were degraded by gamma steri lization in air, with Hylamer liners demonstrating greater property ch anges.