The Radiographic Morphology of Foot Deformities in Patients with Fibrodysplasia Ossificans Progressiva

Abstract

Background: The most consistent deformities that allow early diagnosis of fibrodysplasia ossificans progressiva are the presence of bilateral short first rays and hallux valgus. The purpose of this study was to describe the radiographic features observed in the feet of patients with fibrodysplasia ossificans progressiva. Methods: The radiographs of 26 feet (15 patients with fibrodysplasia ossificans progressiva) were reviewed to evaluate the radiographic changes that occur in the first ray. Variables analyzed were the hallux valgus (HV) angle, the distal metatarsal articular (DMA) angle, the proximal phalangeal articular (PPA) angle, the intermetatarsal (IM) angle, ratio of the lengths of the first and second metatarsal lengths (MT1:MT2), and the first and second ray length ratio. The length ratios were then subtracted from similar ratios in radiographs of age- and gender-matched normal patients previously reported. Results: The proximal phalanx was consistently shortened but morphologically dissimilar from subject to subject. Asymmetry was noted in some patients with bilateral radiographs. The mean HV angle was 28 degrees, and the mean IM angle was 10 degrees. The mean DMA angle was 33 degrees, and the mean PPA angle was 14 degrees. The MT1:MT2 ratio was 0.89, and the mean first ray to second ray length ratio was 0.87. The mean of the differences in the MT1:MT2 and first and second ray length ratios in patients with fibrodysplasia ossificans progressiva compared to the normal controls were 0.05 and 0.01, respectively. Fusion occurred between the abnormal tibial epiphysis of the proximal phalanx and metatarsal head with advancing age, and 68% of the metatarsal heads were fused with the abnormal proximal phalangeal epiphysis. Conclusions: Foot pathology in patients with fibrodysplasia ossificans progressiva is variable but consistently involves an abnormality of the tibial aspect of the proximal phalangeal epiphysis of the hallux. This results in the clinical observation of hallux valgus in these patients. The first metatarsal is consistently shortened, and fusion between the epiphysis of the abnormal proximal phalanx and the shortened first metatarsal head occurs with advancing age.