Metal sensitivity as a cause of bone necrosis and loosening of the prosthesis in total joint replacement.

Loosening of the prosthesis, an important cause of clinical failure following total joint replacement, may be due to faulty implantation of the prosthesis, to trauma, or to infection in the tissues adjacent to the implant. Cases of loosening exist, however, in which the technique of implantation appears to have been satisfactory, in which there is no history of injury and in which there is no evidence by conventional criteria of the presence of infection. It will be argued in this paper that at least some of these cases may be due to sensitivity of the tissues to one of the metals in the alloy of which the prosthesis is composed. With one exception, all the patients described had prostheses implanted in which both components were composed of cobalt-chrome alloy. We believe that the problem of metal sensitivity is likely to be most important with implants of this kind but that it may also occur when an alloy articulates with bone. In contrast, we believe that the problem is least important when either cobalt-chrome alloy or stainless steel is articulated with high density polyethylene. In summary the argument to be presented is as follows. Laboratory and clinical studies have shown that when two cobalt-chrome alloy surfaces are rubbed against each other cobalt and chromium are released into the local tissues, pass into the blood stream to be presented to all body tissues, and finally appear in the urine. It is known that skin sensitivity can develop in response to certain metals implanted in the body, and that cobalt and chromium can produce skin sensitivity. We suggest that in certain patients the release of metal from a prosthesis may result in tissue sensitisation and that this can be detected clinically by a skin patch test in which a soluble salt of the metal (for example cobalt chloride) is used as the test object. We believe that the release of metal from prostheses in metal-sensitive patients causes obliterative changes in the blood vessels supplying the bone into which the prosthesis is implanted and leads to the death of this bone. We suggest that when the bone dies the integrity of the bone-prosthesis bond is prejudiced (probably as a consequence of fibrous replacement of, and fatigue failure in, the dead bone), and that the prosthesis then becomes loose. We now report the following three groups of observations relevant to this argument: 1) a study of the amount of metal in the tissues adjacent to prostheses; 2) a study of metal sensitivity in patients with prostheses; and 3) a study of the histopathology in the tissues adjacent to prostheses in metal-sensitive patients.