Large-diameter total hip replacement bearings

Abstract

In recent years, the use of larger heads has become popular in total hip arthroplasty. This development is the consequence of dislocation being cited as the second most frequent reason for revision and also of high patient expectations with respect to function of their hip replacement. Larger heads have been shown to be an effective measure against dislocation and also have the potential to increase range of motion. However, larger heads always increase the joint friction moment, thereby challenging component fixation in the femur and in the acetabulum. Since larger heads are also associated with greater wear when articulating against polyethylene, there has been a shift to hard-on-hard bearing articulations. In simulators, metal-on-metal bearings demonstrated a particular decrease in wear with increasing head diameter. Initially, it was not appreciated that in situations of poor lubrication and edge loading, the benefit of larger heads is lost, with an increased risk of revision. Large-diameter metal-on-metal bearing couples demonstrated an especially marked increase in revision rates due to cup loosening, excessive metal debris, or taper issues. The challenge now is to find a balanced head size that reduces the rate of early revision due to dislocation, as well as late revision due to lysis, loosening, and other wear debris-related problems. The evidence suggests that the compromise could be a diameter of 32 or 36 mm, depending on the bearing articulation.