Fibrous Dysplasia —
Mutation of Gene GNAS1 leading to inhibition of differentiation and proliferation of bone stromal cells leading to replacement of bone by fibrous tissue and immature woven bone.
Location — Metaphyseal lesion extending into Diaphysis
Age group — 5-30 years
MC site (overall ) – Proximal femur
MC site in craniofacial area – zygomatic maxillary complex
Monostotic – Single bone involvement ( six times more common ) ( usually doesn’t progress )
Polyostotic – Multiple bone involvement ( progresses )
Clinical Presentation : Pain , Deformity and Pathological fracture
Generalised fibrous Dysplasia involving skull and face is called Leontiasis Ossea
X-ray – Multiloculated , translucent lesion expanding the cortex of the bone ( Ground Glass appearance )
In certain cases , surrounded by sclerotic rim called RIND Sign.
In neglected cases of the proximal femur , medial wall collapses leading to Shepherd Crook Deformity.
Biopsy – Chinese letter pattern Treatment