Fatigue fracture of a forearm plate within a long-arm cast.

Open fractures of both left ulna and radius, in which a segment of the radius was found to be missing, occurred in a 27-year-old man. The fractures were treated by open reduction, internal fixation with ASIF semitubular plates, and bone graft. Because of slow radiological union, regrafting was required twice. Approximately six months after the third operation, roentgenograms showed that the bone plate was broken, even though the fractures had been protected in a long-arm cast. The fatigue fracture of the plate, positioned on the posterior surface of the ulna, was presumably caused by the force of the finger flexors, most of which originate above the fracture site, and which were still able to contract because the fingers were not immobilized.