Mechanism for superior subluxation of the glenohumeral joint in fibrodysplasia ossificans progressiva.

ABSTRACT

Progressive heterotopic ossification leads to ankylosis of the major joints in patients who have fibrodysplasia ossificans progressiva. Joint subluxation has not been recognized widely in patients with this disease. The clinical records and radiographs of 79 patients with fibrodysplasia ossificans progressiva were reviewed and, it was found that humeral to chest wall synostosis and subluxation of the glenohumeral joint had occurred in 21% of skeletally immature patients and in 74% of skeletally mature patients. In fibrodysplasia ossificans progressiva, synostosis of the humeral shaft to the chest wall commonly occurs by 7 years of age, well before the age of proximal physeal closure. The continued growth of the proximal humeral physis in the presence of a humeral to chest wall synostosis causes the humeral head to migrate superiorly, thus promoting growth related subluxation. The clinical significance of this finding for patients who have fibrodysplasia ossificans progressiva is unknown, but this unique model will be useful in the study of shoulder biomechanics and growth plate physiology.