The "pelvic digit"--an unusual developmental anomaly.

Five cases of a rare developmental anomaly involving extraskeletal bone formation are described--four in the pelvis and one arising from the 12th rib. Three of these bony growths, called "Pelvic digits" had well developed "joints" or pseudoarticulations. The similarity of this anomaly to posttraumatic myositis ossificans and avulsion injuries of the pelvis (rectus femoris) is pointed out and a differential diagnosis offered.