Characteristics

• A form of avascular necrosis of the femoral head, probably secondary to disruption of the blood supply to the femoral epiphysis.

• Commonest between the years of 4 to 8.

• Male predominance with a ratio of 5 to 1.

• Occurs in 1 in 10,000 and is bilateral in 10%.

Clinical features

• Presents with a limp or, or if bilateral with a painful gait.

• Pain may be referred to the knee or medial thigh.

• On examination, hip abduction and internal rotation are limited.

• Onset may be insidious and thus the child may present late with shortening on the affected side and disuse atrophy of muscle.

• Onset prior to age 8 confers better prognosis.

Radiological features

• Radiographic features are usually well seen by time of presentation.

• Femoral epiphysis appears smaller on the affected side.

• Femoral head sclerosis with adjacent bone demineralisation.

• Slight widening of the joint space.

• Metaphyseal lucent areas – Gage's sign.

• Subchondral fracture best seen on the frog lateral view.

• Sclerotic fragmentation of the femoral head.

• Coxa magna – widened flatter femoral head secondary to remodelling.

• CT may show loss of normal trabecular pattern.

• Bone scan will show decreased uptake followed by increased uptake as repair and secondary degenerative change predominate.

• MRI is sensitive, again with varying appearances depending on the stage.

Management

• Initial management involves bed rest and analgesia. In young presentation disease (< 8 years) non-operative treatment is most common.

• Maintain the femoral head within the acetabulum.

• Surgical osteotomy may be appropriate in selected cases.

• Herring (J. Bone Jt Surg. Am. 2005) has shown surgical management with femoral or pelvic osteotomy is beneficial in late presentation (after age 8) for cases of moderate severity.

• Surgery in late-onset severe disease is controversial.