COMPARISON OF THE WEAR RATES OF 28 AND 32MM FEMORAL HEADS ON CROSS-LINKED POLYETHYLENE ACETABULAR CUPS IN A WEAR SIMULATOR

Abstract

Introduction and Aims: Studies have shown substantial reduction in wear rates in elevated cross-linked polyethylene (crosslinking to a higher degree than that obtained by radiation sterilisation alone). The aim of this study was to test the effect of increased crosslinking and increased head size on polyethylene wear rates.

Method: Four groups of acetabular liners from a single manufacturer were tested: 28mm nominally cross-linked, 32mm nominally cross-linked, 28mm elevated cross-linked, and 32mm elevated cross-linked. Three implants from each group were tested in a 12-station hip wear simulator using 90% bovine serum as lubricant. Liners were articulated with the appropriately sized cobalt-chrome femoral head. Additional liners from each design were subjected only to the same load without motion to serve as load-soak controls to account for any weight gain due to fluid absorption. Gravimetric analysis was performed every 500,000 cycles for a total of 5,000,000 cycles.

Results: Nominally cross-linked liners demonstrated mean wear rates of 14.97±2.70 and 16.92±2.58 milligrams/million cycles for 28mm and 32mm head sizes, respectively. Both of the elevated cross-linked liners had significantly lower wear rates than controls with a mean of 1.51±1.08 and 2.57±1.78 milligrams/million cycles for 28mm and 32mm head sizes, respectively (p< 0.001).

Conclusion: Larger femoral head sizes reduce dislocation in total hip arthroplasty; however, they have been associated with unacceptably high wear rates. The dramatic reduction in wear rates with polyethylene crosslinking even with the larger head size may increase the potential for use of 32mm head components in total hip arthroplasty.