summary Fibrous Dysplasia is a developmental abnormality caused by a GS alpha protein mutation that leads to failure of the production of normal lamellar bone. The condition usually presents in patients who are less than 30 years of age with an asymptomatic lesion that is found incidentally on radiographs. Diagnosis is made with radiographs showing a lesion with ground glass appearance or a "punched-out" lesion with a well-defined margin of sclerotic bone. Treatment is usually nonoperative with bisphosphonates for pain control. Surgical management is indicated for lesions that lead to bone deformities such as scoliosis or coxa vara. Epidemiology Demographics male:female ratio females > males age bracket found in any and all ages onset for 75% of patients at <30 years of age Anatomic location any bone can be involved the proximal femur is most common site, followed by rib, maxilla, and tibia Etiology Genetics associated with GNAS mutation GS alpha protein (chromosome 20q13) activating mutation (affects cAMP signaling pathway leading to increased production of cAMP) high production of FGF-23 which may lead to hypophosphatemia Associated conditions orthopedic manifestations McCune Albright syndrome condition defined by the presence of skin abnormalities (cafe au lait spots in coast of Maine pattern) endocrine abnormalities (precocious puberty) renal phosphate wasting due to FGF-23 (oncogenic osteomalacia) polyostotic fibrous dysplasia obtain AP spine radiographs to look for scoliosis Mazabraud syndrome polyostotic fibrous dysplasia soft-tissue intramuscular myxomas Osteofibrous dysplasia rare form that primarily affects the tibia and is confined to the cortices nonorthopedic manifestations severe cranial deformities with blindness Presentation Symptoms usually asymptomatic and discovered as an incidental finding may have swelling or deformity bone lesions may be monostotic (80%) or polystotic (20%) pain from stress fractures Physical exam inspection cafe au lait spots larger and more irregular borders ("coast of Maine") than neurofibromatosis may or may not be present with fibrous dysplasia by definition present with McCune-Albright syndrome swelling around lesion scoliosis Imaging Radiographs hip/pelvis radiograph central lytic lesions in medullary canal (diaphysis or metaphysis) may have cortical thinning with expansile lesion highly lytic lesions or a ground glass appearance "punched-out" lesion with well-defined margin of sclerotic bone is common modest expansion of bone Shepherd's crook deformity AP spine radiograph vertebral collapse kyphoscoliosis Bone scan usually warm Studies Gross - yellow-white gritty tissue Histology characteristic look of "alphabet soup" or "chinese letters" fibroblast proliferation surrounding islands of woven bone woven bone lacks osteoblastic rimming (osteofibrous dysplasia has osteoblastic rimming) trabeculae of osteoid and bone in fibrous stroma with metaplastic cartilage or areas of cyst degeneration mitotic figures are common Treatment Nonoperative observation indications asymptomatic patients bisphosphonate therapy indications symptomatic polyostotic fibrous dysplasia effective in decreasing pain and reducing bone turnover Operative internal fixation and bone grafting indications symptomatic lesions impending/actual fractures through lesions in areas of high stress (femoral neck) severe deformity neurologic compromise in the spine technique never use autogenous cancellous bone, as the transplanted bone will quickly turn into fibrous dysplastic woven bone use cortical or cancellous allografts intramedullary device more effective than a plate in the lower extremity osteotomies indications coxa vara deformity intertrochanteric osteotomy Differential Fibrous Dysplasia Differential Multiple lesions in young patients Treatment is Observation alone Benefits from Bisphonate therapy Fibrous Dysplasia o o o Eosinophilic granuloma o o Lymphoma o Leukemia o Enchondroma / Olliers / Maffucci's o o Osteochondroma / MHE o o NOF /Jaffe-Campanacci syndrome o o Hemangioendothelioma o Paget's o o Metastatic Disease o Myeloma o Prognosis 1% risk of malignant transformation to osteosarcoma, fibrosarcoma, or malignant fibrous histiocytoma poor prognosis