Extra-articular ankylosis in fibrodysplasia ossificans progressiva.

Forty-four patients with fibrodysplasia ossificans progressiva were identified by a national survey in the United Kingdom. All patients had diagnostic skeletal malformations in addition to ectopic ossification in voluntary muscles and ligaments. Twenty-three of 34 patients (68 per cent) who were traced and examined had limitation of mandibular movement due to ectopic ossification in the muscles of mastication. In three cases such involvement was precipitated by dental therapy and in a further three by other trauma. Operative treatment of the established case was ineffective. Thus management must aim to avoid unnecessary jaw trauma.