Following a vigorous range of motion protocol, 13 ankylosed knees (preoperative motion, 16 degrees +/- 8 degrees to 48 degrees +/- 23 degrees) achieved a significant increase in postoperative range of motion (0 degree +/- 2 degrees to 103 degrees +/- 20 degrees), which was indistinguishable from that achieved by a comparable group of flexible knees (preoperative flexion, 90 degrees or more). The motion gained has been sustained during the two- to five-year follow-up period of the study.