Pinned elbow fracture. X-ray of the arm of an 84- year-old woman showing metal pins (white) supporting a comminuted fracture of the olecranon bone in her elbow joint. The olecranon is a bony prominence on the upper end of the ulna, one of the bones (grey, lower frame) in the lower arm. A comminuted fracture is one where the bone is broken into more than two pieces. It is usually caused by a crushing injury, and extensive trauma to the surrounding soft tissues is often seen. The pieces of bone have been re-aligned and pinned in place, to ensure that they heal properly. The elbow joint occurs where the radius (parallel to the ulna), ulna and humerus (upper frame) meet.