- Defect in osteoblastic differentiation and maturation resulting in replacement of medullary bone with fibrous tissue
- Virtually any bone in the body can be affected.
- It is a nonhereditary disorder of unknown cause.
- Accounts for approx 70-80% of fibrous dysplasias.
- Location in decreasing order of frequency:
- Rib (28%)
- Femur (23%)
- Craniofacial bones (10-25%)
- The degree of bone deformity of the monostotic form is relatively less severe than that of the polyostotic type.
 Polyostotic form
- Account for approximately 20-30% of fibrous dysplasias.
- Sites of involvement are:
- Femur (91%)
- Tibia (81%)
- pelvis (78%)
- Other locations include skull and facial bones, upper extremities, lumbar spine, clavicle, and cervical spine.
- The dysplasia may be unilateral or bilateral, and it may affect several bones of a single limb or both limbs with or without axial skeleton involvement.
 Other features
- Fibrous dysplasia is associated with endocrinopathies in 2-3% of cases
 McCune-Albright syndrome
- Sexual precocity in girls, with polyostotic fibrous dysplasia and cutaneous pigmentation (cafe-au-lait spots).
 Mazabraud's syndrome
- Intramuscular myxomas associated with fibrous dysplasia of bone (written boards question)
 Imaging Findings
Patient #1: Polyostotic fibrous dysplasia
Patient #2: McCune-Albright Syndrome
Patient #3: Shepard's crook deformity
 See Also
 External Links
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