Orthopedics - Oleksa A.P. 2006

Pathophysiology of Joints
Developmental Defects and Congenital Skeletal Anomalies
Fibrous Dysplasia

Fibrous Dysplasia is a benign bone disorder caused by abnormal skeletal development, which can occur sporadically (Stephenson R.B., London M.D., Hankin F.M., Käufer H., 1987). In 1937, Albright and co-workers (Albright F., Bulter A.M., Hamoton A.O., 1937) described the association of polyostotic fibrous dysplasia with characteristic Skin pigmentations and endocrine dysfunction, defining this condition as McCune-Albright syndrome.

Fibrous dysplasia of the bones presents as either a monostotic or polyostotic process, rather than a generalized one. The core of the disease lies in impaired Bone tissue formation originating from the medullar cavity. Normal Bone Formation is replaced by the proliferation of fibro-bone tissue, affecting both the cortical and cancellous bone. Periosteal bone formation remains normal, as the cambial layer of periosteal Cells is not involved in the pathological process. Expanding from the bone cavity, the process very slowly and progressively replaces the cancellous Bone Structure with fibrous tissue, which displaces and thins the remaining cortical layer, leaving it thin yet mature.

Albrecht (1937) described polyostotic fibrous dysplasia (Fig. 68), which is associated with irregular, café-au-lait skin pigmentation and precocious Puberty in girls.

Lichtenstein and Jaffe (Lichtenstein L., Jaffe H.L., 1942) described monostotic fibrous dysplasia, interpreting it as a congenital condition resulting from insufficiently functioning bone-forming mesenchyme. Affected children typically exhibit progressive deformities and pathological fractures within the first month of life due to structural bone impairment.

The exact Etiology of the disease remains unclear to this day. The presence of unilateral—and occasionally bilateral, with a predominance on one side—pathological changes points to early embryonic disruptions in mesenchymal tissue development. There is no conclusive evidence of genetic inheritance.

The pathological process can develop in any bone, but it most frequently localizes in the femoral neck, Tibia, and radius, and occasionally in the Ribs, Skull base, and facial bones.

Fibrous dysplasia manifests in childhood, but due to its slow progression, it is usually diagnosed much later. The initial sign of the disease may be bone curvature or another deformity, and occasionally a pathological fracture. When the process involves the facial bones, facial Asymmetry and deformity occur.

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Fig. 68. Congenital Spondyloepiphyseal Dysplasia complicated by Scoliosis and degeneration of the femoral heads (Grogan D.P., Ganel A., 1997).

The Diagnosis is established based on X-ray and histological examinations.

Histological analysis of fibrous dysplasia reveals a relative consistency of changes before, during, and after puberty (Marris W.H., Dudley H.R., Barry R.J., 1962). Histology demonstrates pathological bone changes resembling those seen in hyperparathyroidism, alongside prominent fibrous metaplasia of the Bone Marrow and normal osteoblastic periosteal function.

Routine Blood tests show no pathological deviations, though alkaline phosphatase activity may be slightly elevated in cases of polyostotic lesions.

Radiographic findings (Fig. 69) reveal focal radiolucencies within the bones, filled with bone tissue of varying density and extending into the cortical layer, which indicates reduced bone remodeling. Frequent fractures, microfractures, and "shepherd's crook" deformities of the proximal Femur are classic diagnostic features. Café-au-lait skin pigmentation presents with irregular borders. Stephenson et al. (Stephenson R.B., London M.D., Hankin F.M., Käufer H., 1987) analyzed serial bone sections in fibrous dysplasia. Overall, Treatment of upper extremity lesions with minimal functional impairment was successful in 88% of cases, which was not observed in lower extremity bone lesions. Among patients older than 18 years, conservative therapy yielded satisfactory results in 89 out of 100 cases, whereas patients treated with curettage and bone grafting showed unsatisfactory outcomes.

The failures were attributed to graft resorption or disease recurrence. This suggests that the condition is quite severe and presents challenges when treated with curettage alone. Local resections, radical resections, and amputations are key to successful treatment (Stephenson R.B. et al., 1987).

Fig. 69. Polyostotic fibrous dysplasia involving the radius and tibia (Crawford A.A., Hamblen D.L., 1990).

In cases of pathological fractures, external fixation osteosynthesis yields favorable results in 86% of cases, regardless of the patient's age. The mechanical strength of the bone depends on its structural restoration following treatment and the absence of disease progression or recurrence.