Perthes Disease

Perthes disease (Legg-Calve-Perthes disease) is idiopathic avascular necrosis of the femoral head epiphysis in childhood, presenting as a limp with hip, thigh or knee pain.

It most often affects children aged 4 to 8, and boys about 4 times as often as girls. The head passes through necrosis, fragmentation and healing over several years, and the final head shape decides the long-term outcome.

Hip pain referred to the knee is the classic pitfall. Early radiographs may be normal, so a persistent limp with normal films still needs referral.

In this age group the femoral head depends mainly on the lateral epiphyseal vessels from the medial femoral circumflex artery. The growth plate blocks metaphyseal supply and the ligamentum teres contributes little, so the head is vulnerable when these vessels are interrupted.

The Waldenström stages:

• •Initial: necrotic bone appears dense; a subchondral fracture (crescent sign) may show on the frog-lateral view
• •Fragmentation: dead bone is resorbed and the head may collapse; it is at its softest here
• •Reossification: new bone forms and the final head shape is set
• •Remodelling: further reshaping with growth until skeletal maturity

Containment is the central principle. The acetabulum acts as a mould: a softened head kept inside it tends to heal round, while a head that extrudes laterally deforms and leads to early osteoarthritis. Younger children have more growth left to remodel, so they generally do better.