Characteristics

• Commonest hip disorder of adolescence (male 13 to 16 years, female 11 to 14 years).

• Commoner in boys with a ratio of 3 to 1.

• Occurs in approximately 2 in 100,000.

• Commoner in obese, but active, patients.

• Unknown aetiology, although genetic and traumatic theories have been proposed.

• Usually seen during a period of rapid growth when the physis appears to be more susceptible to shear forces.

• A history of trauma is given in up to 50% of cases.

• 60% are bilateral.

• Stable (able to weight bear) are distinguished from unstable (not weight bearing) hips. Unstable hips have a 50% risk of future femoral head AVN.

Clinical features

• Presents with pain and a limp, not necessarily localised to the hip.

• Depending on the chronicity, limb shortening with a degree of external rotation may be present.

• Muscle atrophy occurs in delayed presentation.

• Pain and limited internal rotation on examination.

• Considered chronic if symptoms greater than 3 weeks.

Radiological features

• PA and ‘frog leg’ views are the standard views.

• Widening of the epiphysis with metaphyseal irregularity.

• Posteromedial displacement of the femoral head; this is seen as failure of a line, drawn along the superior femoral neck, to intersect with the femoral head.

• Epiphysis appears smaller due to posterior slippage.

• Slippage may only be seen on the frog leg view – but avoid frog view if the hip is ‘unstable’.

• New bone formation (buttressing) seen late.

• Late findings include subchondral sclerosis, cyst formation, osteophyte formation and narrowing of the joint space.

• Ultrasound can be a useful adjunct showing an effusion with early slippage.

• MRI (bilateral) to look for ‘pre-slip’ if pain but normal X-rays.

Management

• Aimed at preventing further slippage and maintaining function. Always consider the contralateral hip.

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