Total Hip Replacement with a Trunnion Bearing Prosthesis:Biomechanical Principles and Preliminary Clinical Results

The biomechanics are presented of a bushing principle forming the basis for a trunnion bearing prosthesis in total hip replacement. The femoral stem is equipped with a trunnion on to which a cylindrical plastic sleeve is applied. On top of this a metal casing is placed which forms the femoral head. On flexion-extension this remains stationary in the acetabular cup and motion occurs between the trunnion and the cylindrical sleeve. Friction between head and cup is reduced to a minimum, decreasing the risk of loosening. A follow-up study of 61 hips replaced by the trunnion bearing prosthesis was performed 2.5 years postoperatively. Eighty-eight per cent were considerably improved. There was one deep infection and two femoral stem loosenings.