SummarySensitivity to chromium, cobalt, nickel, molybdenum, vanadium, and titanium was studied by patch tests in 50 patients who had received total joint replacements.Nineteen (38%) were sensitive to one or more ofthe metals. In 23 patients non-traumatic failure of the prosthesis had occurred, and 15 of these patients were sensitive to metal. Out of 27 patients with no evidence of prosthesis loosening, four were sensitive to nickel and cobalt or nickel only. Dermatological reactions occurred in 13 patients after surgery; in only eight, however, was there evidence of metal sensitivity. These findings indicate that metal-on-metal total joint replacements may sensitise the patient to metals contained in the prosthesis. Although there is a high incidence of prosthesis failure among metal-sensitive patients it remains uncertain whether the loosening causes the sensitisation or vice versa. IntroductionThere are several well established causes of the loosening of joint prostheses, such as infection, faulty implantation, trauma, and, in early types ofprosthesis, design faults. Recently, however, the development of a state of immunological sensitivity to the metallic components of the joint replacement has been suggested as a further cause of loosening. It is well established that in vivo during the wear of metal-on-metal bearings of prostheses grey-staining particulate material is found in tissues.' 2 These particles have been shown by x-ray fluorescence spectroscopy to be metallic.3 In patients with metal-on-metal hip prostheses both cobalt and chromium can be detected, often in considerable quantities, in the blood, urine, and hair. 4 Recently there have been several reports of patients suffering from urticarial or ezcematous dermatitis, which has been attributed to the presence of an implanted metallic prosthesis or other appliance.5-8 Patch tests showed these patients to be positive

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Isografts of cortical bone were tranplanted subcutaneously in the rat and the rate of osteogenesis 12 to 14 days later was assessed by measurement of 85Sr uptake and by histology. Some grafts were implanted complete whereas others had had one or more of their cellular components (viz. periosteum, endosteum, osteocytes, marrow) removed by mechanical or enzymatic pretreatment. From an analysis of the differences in osteogenesis between grafts devoid of different combinations of cellular components, the contribution of each component to osteogenesis was determined. The results indicate that the endosteal lining cells and marrow stroma together produce more than half of the new bone, the periosteal cells contribute about 30%, the osteocytes possibly make a small (10%) contribution, and the free, hemopoietic cells of the marrow make no significant contribution. Evidence about the relative contributions to osteogenesis of graft and host cells is reviewed and the possible osteogenetic role of bone marrow is discussed.

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