Changing Pattern of Femoral Deformity During Growth in Polyostotic Fibrous Dysplasia of the Bone: An Analysis of 46 Cases

Background: In polyostotic fibrous dysplasia (PFD) affecting the femur, 6 types of stable femoral deformities have been identified, ranging from the mild type 1 to the most severe type 6. The purpose of our study was to identify the type of deformity present at diagnosis in children with PFD affecting the femur, and to investigate possible changes in the original type with growth. Methods: Twenty-seven children affected by either PFD or McCune-Albright syndrome, with 46 affected femurs, were consecutively observed from 1994 to 2010. Radiographs of the pelvis and femurs were taken at diagnosis, and afterward at regular intervals of 6 to 12 months depending on the clinical evolution of each case. Radiographs of the femurs taken at 3 and 7 years after diagnosis were selected to assess the evolution of the femoral deformity. Deformities were classified according to the femoral shape, neck-shaft angle value, and the presence of shepherd's crook deformity evaluated on AP radiographs. Results: The average age of the patients at diagnosis was 5 years (range, 2 to 11 y). At diagnosis, 30 femurs were type 1; 12, type 2; 1, type 3; 1, type 4; and 2, type 5. Three years later, 39% of the femurs had maintained the original deformity present at diagnosis, whereas only 13% did so 7 years after diagnosis. Predictors of change to a more severe type were: younger age at diagnosis, McCune-Albright syndrome, rapid spreading of fibrodysplastic tissue from the trochanteric area to the proximal femoral shaft, cortical thinning of the proximal femur, calcar osteolysis, and presence of an intertrochanteric cystic-like lesion eroding the calcar. Conclusions: In children with PFD affecting the femur, 61% of the femoral deformity present at diagnosis switched to a more severe type of deformity within 3 years from diagnosis, whereas 87% either shifted to a more severe type of deformity or already had corrective surgery within 7 years after diagnosis.