Fatigue fracture of the interlocking nail in the treatment of fractures of the distal part of the femoral shaft.

The clinical and mechanical factors predisposing to a fatigue fracture of an interlocking nail were studied in seven patients who were treated for a fracture of the distal part of the femur. In all patients, the fracture of the femur was five centimeters or less from the more proximal of the two distal screw-holes. Finite-element analysis revealed that the stress on the nail exceeded its fatigue endurance limit and that the femur had to regain 50 per cent of its original stiffness through healing to accommodate weight-bearing without the risk of fatigue failure of the nail. The risk of fatigue failure may be minimized by using nails that have a larger diameter and by avoiding early weight-bearing.