Characteristics

• Can occur at any age. Commonest in 10–30 year olds with the majority arising prior to epiphyseal fusion.

• Any bone may be affected but most commonly occur in long-bone metaphyses, especially the lower limb.

• Aetiology unknown.

Clinical features

• Pain associated with expansile lesions.

• Pathological fractures may occur.

• May be visible or palpable if sufficiently large.

Radiological features

• Well-defined radiolucent cyst, often eccentric within bone. Marked ‘soap-bubble’ expansion may be seen.

• Usually trabeculated with a thin intact cortex (narrow transition zone).

• No periosteal reaction (except when fractured).

• Within the spine, posterior elements are more commonly involved.

• May be mistaken for other cyst-like lesions – see Bone cysts.

• MRI/CT – fluid levels within cyst due to blood sedimentation (in up to 35%).

Management

• Curettage and bone grafting, or substitute grafting.

• If the ABC recurs, then consider bone cement rather than bone graft in the revision procedure.