Pinned broken arm (2 views). Coloured X-ray of the forearm of a 34 year old man, showing the pinning of a double compound fracture. Both radius and ulna lower arm bones have been fractured. Steel plates have been surgically inserted and screwed against each bone at the point of fracture to immobilise and align the broken bone, so that the ends can knit together and heal properly. The broken ends of bone had separated and could have pierced the skin. The radius is the larger forearm bone, aligned with the thumb of the hand (at top). The smaller ulna is at right. Most fractures are due to sudden injury.