Fatigue failure of an AO spiral blade.

We report an unusual case of a femoral neck stress fracture leading to the fatigue failure of an AO spiral blade. An unreamed femoral nail with a spiral blade was inserted to treat an unstable subtrochanteric femoral fracture. which lead to fracture union at 5 months. Eight months post-operatively the patient started to complain of left hip pain. Serial radiographs revealed progressive osteoporosis of the proximal femur possibly due to the stress sharing effect of a stiff intramedullary device, which continued to bear a significant amount of the transmitted load. The cause of pain was a stress fracture of the femoral neck and the AO spiral blade, which only became radiologically visible 4 months after the start of the symptoms (1 year after the initial operation). The implant was removed and replaced by a cemented hemiarthroplasty. This case reaffirms the difficulty in diagnosing a stress fracture through a metallic implant. The delay in diagnosis may be shortened if stress fracture were included as an expected complication following an intramedullary nailing.