Late Fatigue Fracture of a Modern Cemented Forged Cobalt Chrome Stem for Total Hip Arthroplasty

We report 10 fatigue fractures of a modern, cemented, cobalt chromium alloy stem (Osteonics Omnifit) for total hip arthroplasty occurring between 1995 and 2004. The primary total hip arthroplasties had been performed between 1989 and 1996. The average age at the time of surgery was 54 years (range, 34-70 years), and the average body mass index was 29 (range, 20-38). The time in situ of the prosthesis at the time of fracture averaged 8 years (range, 4-12 years). Intermediate follow-up radiographs before the fracture were available in 7 cases, all of which demonstrated loss of calcar support. Scanning electron microscopy of the fracture surfaces in 3 of the components showed porosity near the initiation site. Metallography of polished and etched cross sections near the fracture surface revealed large grain size. In the presence of a spontaneous onset of thigh pain at intermediate follow-up in patients with this stem, particularly if associated with loss of calcar support, a fatigue fracture should be considered.