Failed femoral stems in total hip prostheses. A report of six cases.

Six femoral stems of total joint prostheses failed and were studied. These included two short-neck Müller, one standard Müller, one new design long-neck Müller, and two Charnley prostheses. In addition, reference is made to another failed Charnley prosthesis which had not required revision at the time of the study. Reoperation and replacement of the femoral component was required in all six cases. Metal fatigue appeared to be the cause of failure in all instances. Metallographic examination of the removed prosthesis revealed no underlying defects in one prosthesis. In the other five prostheses metallurgical defects were found. Varus placement of the femoral prosthesis or loosening of the cement-prosthesis bond, or both, were identified in five of the six and were thought to have led to overload. A combination of metal defects and loosening or malpositioning was thought to be responsible for the failures. It was further indicated that current designs should be regarded as marginal in relation to long service life, until more fatigue information is available on the metallic materials currently in use.