You are in: eMedicine Specialties > Orthopedic Surgery > NEOPLASMS Fibrous DysplasiaArticle Last Updated: Jun 1, 2005AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Mark Clayer, MD, MBBS, FRACS, FAOrthA, Head of Musculoskeletal Tumor Service, Queen Elizabeth Hospital; Senior Visiting Medical Specialist, Department of Orthopaedics and Trauma, Royal Adelaide Hospital and Women's and Children's Hospital Mark Clayer is a member of the following medical societies: Australian Medical Association and Australian Orthopaedic Association Editors: Howard A Chansky, MD, Associate Professor, Department of Orthopedics and Sports Medicine, University of Washington Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Sean P Scully, MD, PhD, Professor, Department of Orthopedics, University of Miami; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Harris Gellman, MD, Consulting Surgeon, Broward Hand Center, Voluntary Clinical Professor of Orthopedic Surgery and Plastic Surgery, Departments of Orthopedic Surgery and Surgery, University of Miami School of Medicine Author and Editor Disclosure Synonyms and related keywords: bone dysplasia, dysplastic disorder, connective tissue, fibroosseous tissue, lamellar bone, monostotic fibrous dysplasia, polystotic fibrous dysplasia, precocious puberty, skin pigmentation, McCune-Albright syndrome, Mazabraud's syndrome INTRODUCTIONSection 2 of 12
  Fibrous dysplasia is a developmental dysplastic disorder of bone in which immature woven bone is formed directly from abnormal fibrous connective tissue. It is characterized by expanding fibroosseous tissue within affected bones and predominantly is a lesion of the growing skeleton. It is termed a dysplasia because of the inability of involved tissue to form mature lamellar bone from the immature, woven precursor. Monostotic fibrous dysplasia affects only one bone, most commonly the ribs, proximal femur, and craniofacial bones. Polyostotic affects many bones, up to 75% of the skeleton. Monostotic fibrous dysplasia is 7-10 times more common than polyostotic fibrous dysplasia. It also can be associated with systemic conditions, including precocious puberty and skin pigmentation (as in McCune-Albright syndrome) or soft-tissue myxomas (as in Mazabraud's syndrome). History of the ProcedureLichtenstein, in 1938, and Lichtenstein and Jaffe, in 1942, described fibrous dysplasia in 2 classic papers as a congenital or developmental anomaly caused by disturbance of the bone-forming mesenchyme. ProblemDisorganized, immature bone surrounded by primitive fibrous tissue cannot mature into normal lamellar bone in affected areas. This may result in loss of mechanical integrity of the bone and predispose the patient to fracture or deformity, particularly in weightbearing bones. Even prior to fracture, pain can be disabling. In addition, fractures usually heal with more dysplastic bone, thereby potentiating the problem of mechanical insufficiency. Rarely, fibrous dysplasia may become more aggressive and dedifferentiate (desmoplastic fibroma) or undergo sarcomatous transformation (as in osteosarcoma, fibrosarcoma, malignant fibrous histiocytoma (MFH), dedifferentiated chondrosarcoma). Risk factors include polyostotic form, past radiation therapy, facial bone involvement, and Albright syndrome. FrequencyMost cases are asymptomatic, so true incidence is unknown. Fibrous dysplasia comprises approximately 10% of all benign bone tumors. The monostotic form is about 7-10 times more common than the polyostotic form. Usually, fibrous dysplasia presents clinically in children and adolescents, with a median onset age of 8 years. Most cases will be manifested by age 30 years. Males are affected more often than females, except in McCune-Albright syndrome, in which females are affected more often than males. EtiologyAny theory of pathogenesis must explain clinical features of fibrous dysplasia. At a fundamental level, fibrous dysplasia appears to be either a disorder of postnatal cancellous bone maintenance in which bone undergoing physiologic remodeling is replaced by an abnormal proliferation of fibrous tissue or a developmental abnormality of the bone-forming mesenchyme. At the molecular level, fibrous dysplasia is caused by sporadic mutation of the GNAS1 gene that encodes the alpha subunit of the stimulatory G protein (G1). The exact biochemical pathway that leads to the clinical phenotype is unknown. The somatic mutation occurs after conception; the extent and pattern of disease depend on the stage of development and location at which the mutation occurs. PathophysiologyInvolved bone consists of immature, relatively undifferentiated fibrous connective tissue that fails to produce normal amounts of collagen or to orientate appropriately to the lines of mechanical stress. ClinicalMost commonly, fibrous dysplasia affects the ribs and often is asymptomatic. Other sites typically affected include the femur, tibia, maxilla, and skull. Patients usually seek medical care because of either painful swelling and deformity or a pathologic fracture through a weakened bone. Nonskeletal manifestations include abnormal cutaneous pigmentation (jagged "coast of Maine" border), precocious puberty, hyperthyroidism, Cushing disease, hyperparathyroidism, and hypophosphatemic rickets. Albright syndrome is defined as the triad of precocious puberty, polyostotic fibrous dysplasia, and cutaneous pigmentation. Typically, only females are affected by precocious puberty, but the other endocrine abnormalities occur equally in males and females. All of these abnormalities are thought to be due to the same underlying mutation. INDICATIONSSection 3 of 12
More than 80% of upper-extremity lesions respond to nonsurgical management. Surgical treatment is indicated in the prevention or treatment of fractures or deformity or to alleviate chronic pain that is secondary to loss of mechanical integrity of bone. Surgical indications can be summarized as follows:
RELEVANT ANATOMYSection 4 of 12
This condition can affect almost any bone in the body. The relevant anatomy is that of the bone involved. CONTRAINDICATIONSSection 5 of 12
No specific contraindications to surgical intervention exist; however, care must be used in the skeletally immature patient. Internal fixation of long bones to prevent deformity may necessarily involve penetration of the physis or physes. Unlocked intramedullary fixation should be considered, as it is least likely to restrict growth. WORKUPSection 6 of 12
Lab Studies
Imaging Studies
Diagnostic Procedures
Histologic FindingsThe gross findings of fibrous dysplasia include a centrally located tan to gray-white gritty-feeling lesion. The microscopic appearance shows a fibrous/collagenous matrix with randomly oriented bone or fiber trabeculae that are formed by osseous metaplasia of spindled stromal cells. The spicules of immature bone that are produced are short and irregular and are not lined by osteoblasts. The appearance has been described as that of Chinese letters. Small nodules of cartilage are found within the fibrous matrix in 10% of cases. Staging
TREATMENTSection 7 of 12
Medical therapyTreatment is usually conservative and primarily to prevent deformity. Treat any underlying endocrine disturbance. In upper extremity lesions, more than 80% respond to nonsurgical management. No specific medical treatment exists for the bone disease, although early evidence suggests that vitamin D and bisphosphonates (after physeal closure) may be helpful in ameliorating pain and possibly in reconstituting lesions with normal bone. Bisphosphonates used have included alendronate, pamidronate, etidronate, risedronate, tiludronate and zoledronate. Pamidronate has been used the most and is usually given intravenously as an infusion of 180 mg over 3 days every 6 months. Concomitant calcium (500-1500 mg/day) and vitamin D2 (800-1200 IU/day) must be given to avoid secondary hyperparathyroidism. Surgical therapyCurettage and replacement of the bone defect with autograft or allograft usually result in resorption of the graft into fibrous dysplasia. Use of allograft or cortical autograft usually delays this conversion, as it is more resistant to resorption and replacement by dysplastic bone. Long bones require stabilization only, and this is best achieved by intramedullary nail fixation. Expendable bones can be treated by excision. Deformity may require corrective osteotomy and internal fixation. A vascularized fibular graft has been used for some lesions with success. Intraoperative detailsThe dysplastic bone can be quite difficult to ream and direct a guide wire down the canal without perforation. Follow-upFibrous dysplasia rarely undergoes remission, and it is unusual for grafted bone or bone substitutes to be replaced by more fibrous dysplasia. For this reason, it is appropriate to periodically monitor the disease progression, especially in the skeletally immature patient. Once skeletal maturity has been achieved, it is unusual for fibrous dysplasia to progress. The main role of the follow-up, therefore, is to prevent deformity as a result of the disease. The author follows up with yearly plain radiographs of the involved area or areas until skeletal maturity. Early intervention with internal fixation of involved bones may be important in the prevention of deformity. COMPLICATIONSSection 8 of 12
Fracture is the most common complication. In polyostotic disease, fracture occurs in approximately 85% of cases. Deformity may occur in weightbearing bones. Malignant transformation occurs in less than 0.5% of cases. It is more likely to occur if polyostotic disease exists or following treatment with radiation therapy. The risk of malignant transformation in the presence of McCune-Albright syndrome has been reported to be 4%. OUTCOME AND PROGNOSISSection 9 of 12
The recurrence rate has been reported at 21% following curettage and grafting but probably is closer to 100% if patients are monitored for many years. Unless malignant transformation develops, fibrous dysplasia is not a life-threatening disease. The lesions tend to stabilize as skeletal maturity is reached. The risk of malignant transformation has been reported to be 0.5% in monostotic fibrous dysplasia, 4% in McCune-Albright syndrome. FUTURE AND CONTROVERSIESSection 10 of 12
Recent major advances have occurred in understanding the molecular basis of fibrous dysplasia. The mutation has been identified, but the actual pathways that lead to abnormal osteoblast differentiation and function are just beginning to be understood. In the future, effective nonsurgical treatments may be possible. The risk of local recurrence is high, so the decision to treat must be made with informed consent to avoid inappropriate expectations. In general, the goals of surgery should be to stabilize the bone and relieve pain, rather than to excise the involved bone. The condition often is found incidentally, and the need for prophylactic treatment may be difficult to accept for an asymptomatic or minimally symptomatic patient. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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