Ten uncemented total hip replacements were performed in 1975 using an implant in which the cobalt-chrome femoral stem was coated to give a porous surface. In all but one case a high-density polyethylene head was used. The radiological changes in the upper femoral shafts were assessed between three and nine years later. Seven showed extensive stress-relieving changes, loss of calcar, stress fractures at the root of the lesser trochanter with subsequent detachment, and osteoporosis followed by avulsion of the greater trochanter. In these seven patients the lower part of the stem appeared to be soundly embedded, although in only one was there evidence of bony incorporation. It is suggested that if the fixation of a fully coated implant of this sort remains sound, gross atrophy of the upper femoral shaft develops after five years. This atrophy, associated with an implant which can be removed only at the expense of further bone destruction, presents substantial problems if revision is needed.

The occurrence of an osteosarcoma at the site of a cobalt-chrome total hip replacement is described, and the possibility of the tumour arising as a result of the liberation of cobalt particles is discussed. The experimental and clinical evidence relating tumour formation to the presence of particulate metals, and to the presence of solid and particulate polyethylene, is presented. It is considered that the risk of tumour formation at the site of any total hip replacement is very small.