Charnley low-friction arthroplasty

Surgeons were already replacing hips before John Charnley; what he pioneered was a successful low-friction version. Charnley, an orthopedic surgeon at Wrightington Hospital, set out to reduce friction between the head of the femur and the socket of the pelvis. In 1956 he tried polytetrafluoroethylene, or Teflon, as a synthetic cartilage. It wore away quickly and provoked an intense reaction in the surrounding tissue. In May 1961 he described his approach in The Lancet as a new operation.

The answer he settled on was ultra-high molecular weight polyethylene, which was strong, wore slowly and ran with little friction. He also cut the turning force of the metal head against the socket by making the femoral head small, 22.2 mm across. Both parts were fixed with cold-cured polymethyl methacrylate. Bone cement does not glue an implant to bone; it fills the space around it and holds it in place like grout. The combination of materials and design, dated to November 1962, became known as the Charnley concept.

Doubts later arose over whether the results reported by specialist hip centres could be matched in ordinary hospitals. A study published in BMC Musculoskeletal Disorders in 2008 followed 404 Charnley low-friction arthroplasties implanted between 1976 and 1993 by general orthopedic surgeons in a general hospital. Four percent of the hips dislocated and 3.5 percent developed deep infections. At 25 years, 83 percent of both stems and cups were still in place, with better survival in patients over 60, results similar to those from centres devoted to hip surgery.