Six femoral stems of total joint prostheses failed and were studied.
These included two short-neck Muller, one standard Muller, one new design
long-neck Muller, 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.