Analysis of wear and oxidation on retrieved bipolar polyethylene liner.

Abstract

For bipolar prostheses, most of the previous studies attributed the occurrence of osteolysis to wear debris generated from the bearing surface. We looked closely into the wear debris and reported on our findings with respect to the oxidation index and the rate of wear in ultra-high molecular weight polyethylene (UHMWPE) inserts retrieved from bipolar prostheses after various spans of time in vivo. The inserts were retrieved from the heads of three types of bipolar prosthesis (UH1, UPF1, UPF2). We retrieved 24 bipolar prostheses from 23 patients whose mean implantation period was 10.0 years (2.7-15.4 years). All the retrieved polyethylene had a burnished bearing surface. In all, 92% (22/24) of these inserts had indentation and roughness at the rim and flange, suggesting neck-cup impingement; periprosthetic fracture occurred in the other two inserts. The mean linear wear rate was 0.035 mm per year. The average maximum oxidation index for the inserts with osteolysis was 3.34, and it was was 3.49 for the inserts without osteolysis. We, therefore, could not detect any significant difference between the aforesaid groups of inserts. The results strongly suggest that most of the polyethylene wear debris was not generated from the bearing surface. Moreover, the wear debris generated from neck-cup impingement may well be the cause of an inflammatory reaction, which in turn has a strong potential to become the primary cause of osteolysis.