METAL ON METAL BEARINGS IN HIP-ARTHROPLASTY

Periprosthetic osteolysis caused by wear debris released from the bear ing surface of polyethylene components is the major problem in contemp orary hip arthroplasty. Several types of metal on metal prostheses wer e developed in the 1960s, but by the mid 1970s they were completely di splaced by polyethylene bearings. There have been several generations of all metal components with significant variation in design, toleranc es, and bearing surface quality. A number of these hips have survived for more than 25 years because of low wear rates and minimal osteolysi s. Identification of the characteristics that contributed to long term function is important. The historical development and clinical result s of metal on metal hip arthroplasties are presented. Factors that led to the abandonment of the metal on metal bearings are related to: (1) the early success of the Charnley prosthesis; (2) the frictional torq ue issue; (3) carcinogenesis concerns; (4) metal sensitivity concerns; (5) high infection rates; and (6) increased strain rates in periprost hetic bone and fatigue fractures of the acetabular floor. The accumula ted experience to date enables one to evaluate all the factors with a different perspective and makes the use of newer metal on metal bearin gs a viable option in younger patients.