Spontaneous fractures of the olecranon process in rheumatoid arthritis.

Spontaneous fractures through the olecranon process occurred in 3 patients with long-standing rheumatoid arthritis. In each case the elbow was severely damaged, particularly in the midportion of the trochlear notch, which was thinned either by erosion or cyst formation. The thin trichlear notch is the weak pivot point of a lever (the olecranon process) which pivots on the distal humerus. Excess stress on the lever, by the action of the triceps on the olecranon process, will produce a fracture at the weakest point: the midtrochlear notch.