Traumatic fractures of heterotopic bone in patients who have fibrodysplasia ossificans progressiva. A report of 2 cases.

Fibrodysplasia ossificans progressiva is an extremely rare genetic disorder characterized by the formation of a heterotopic skeleton that is histologically, biomechanically, and metabolically indistinguishable from the normotopic skeleton. Isolated cases of traumatic and pathologic fractures have been reported in the normotopic skeleton of patients who have fibrodysplasia ossificans progressiva, but to the authors' knowledge there have been no detailed reports of traumatic fractures in the heterotopic skeleton of patients who have this disease. Reported here are 2 children with fibrodysplasia ossificans progressiva who sustained traumatic fractures of heterotopic bone around the elbows. In both children, the fractures healed uneventfully with normal-appearing callus. These 2 extremely rare cases suggest that the biologic response to fractures in the heterotopic skeleton appears indistinguishable from that in the normotopic skeleton in patients who have fibrodysplasia ossificans progressiva.