Femoral Stem Failure and Ectopic Bone Formation in Total Hip Arthroplasty

In 4 cases of fracture of the femoral stem in total hip arthroplasty (THA), 3 were preceded by clinical and radiographic evidence of loosening and the last was not. Each developed a significant amount of ectopic bone. Stem failure in THA is a continuum progressing in some cases from ectopic bone formation and calcar resorption to stem loosening. An association between ectopic ossification and stem loosening is determined by grading the quantity of new bone not only by the amount but also by its spatial relationship with the implant. Observation on a large number of cases by the method of DeLee, Ferrari, and Charnley is required to prove or disprove the effect of ectopic bone on stem failure. In any case, patients who develop ectopic bone should be restricted in their activities.