RADIOGRAPHIC AND SCINTIGRAPHIC FEATURES OF MODELING AND REMODELING INTHE HETEROTOPIC SKELETON OF PATIENTS WHO HAVE FIBRODYSPLASIA OSSIFICANS PROGRESSIVA

To characterize the radiographic and scintigraphic features of modelin g and remodeling in the heterotopic skeleton of patients who have fibr odysplasia ossificans progressiva, radiographs from 47 patients and ra dionuclide bone scans from 12 of those patients, all of whom had a con firmed diagnosis of the disease, were reviewed. A wide range of normal bone modeling and remodeling features was seen in the heterotopic ske leton of all but the youngest two (age, 1 year) of the 47 patients. Ch aracteristic features of normal bone modeling identified on radiograph s of the heterotopic skeleton included: (a) the development of tubular and flat bones with mature cortical and trabecular organization; (b) the presence of well defined cortical-endosteal borders enclosing medu llary canals; and (c) the presence of metaphyseal funnelization in iso lated ossicles or at sites of synostoses. Characteristic features of n ormal bone remodeling identified on radiographs of the heterotopic ske leton included: (a) the response of heterotopic bone to weight bearing stress with osteosclerosis of use and osteopenia of disuse, and (b) t he resistance of heterotopic bone to fatigue failure with the absence of pathologic fractures and stress fractures. Radionuclide bone scans in 12 patients showed that remodeling of mature heterotopic bone occur red at a rate consistent with that of mature normotopic bone. This stu dy documents the radiographic and scintigraphic features of a heteroto pic skeletal system in 47 patients who have fibrodysplasia ossificans progressiva. These data provide additional support for the hypothesis that the genetic defect leading to the formation of a heterotopic skel eton involves normal skeletal morphogenesis at heterotopic sites.