Studies of host response to orthopedic implants and biomaterials.

The use of implanted biomaterials in orthopedic surgery has increased rapidly during the past two decades. Total joint replacement of the hip or knee joint has become common treatment; at the same time, an increasing number of fractures are treated with osteosynthesis. The original Charnley low-friction arthroplasty of the hip is still widely used and gives in large series excellent results. Aseptic loosening of this arthroplasty has been thought to be due to wear debris of the methylmethacrylate used for fixation of the implants, or to debris generated from wear of the polyethylene socket. To date, many different materials have been tried in order to reduce wear and generation of macrophage irritating submicron sized particles, or to provide more biocompatible components. However, trials to improve the methylmethacrylate cement or to invent better polyethylenes have often failed. Diamond coating of the metallic components seems promising: there is less wear and diamond is very biocompatible in bulk and small particulate form. Biodegradable implants have also been found useful in treating fractures. Bioactive bioabsorbable materials may also make possible a tissue engineering approach and can be used as carriers for selected drugs and cytokines. Because many promising materials and designs have failed in clinical use, extensive theoretical and experimental testing is mandatory before introducing new materials and implants in a clinical setting.