Wear and Loosening in Cemented Hip Arthroplasty

Abstract: The mechanisms of loosening in total hip arthroplasty (THA) and the role of polyethylene (PE) wear debris in this process is unclear. Radiographic measurements showed that THA with 32 mm heads have about 3 times greater volumetric wear than those with 22 mm heads. If PE debris were the main cause of loosening, then there should be an obvious difference in revision rates between the prostheses with these two head sizes. However, the analysis of revision rates, due to aseptic loosening, showed no significant difference. These findings do not support the hypothesis that wear debris is the main cause of loosening. The intracapsular pressure and ultrasonographic synovitis in THA with loose components was studied. The pressure was high and with cyclic alterations dependent on hip joint movements. The synovitis in loose THA was more pronounced than in stable ones. There was a significant correlation between the intracapsular pressure with the hip in extension with inward rotation and synovitis. These results suggest that increased pressure and synovitis is important in loosening of THA. The correlation between synovitis, wear and radiographic loosening was studied. There was a significant correlation between volumetric wear and synovitis. Hips with cup loosening had significantly greater wear and synovitis than the others. In THA with loose cups the PE wear was higher than in those with loose stems. This indicates that PE debris is of certain importance in loosening of acetabular components, but of less significance in loosening of stems. The experimental study showed that bone cement, if left inside PE cups during curing, contaminates the articulating surface of the cups with cement debris. In clinical situations such contamination may predispose to increased wear.