In Legg-Calvé-Perthes disease, the Catterall group III classification describes which extent of femoral head involvement?

• A Only the anterior segment of the head is involved; epiphysis is not at risk
• B Three-quarters of the head involved with anterolateral loss; only posterior segment intact; head-at-risk signs present ✓
• C Anterior segment and the central portion affected; posterior segment uninvolved
• D Total head involvement with central sequestrum

Explanation

Catterall's classification of Perthes disease: Group I — anterior involvement only; Group II — anterior and lateral involvement with intact posterior; Group III — three-quarters of the head involved (anterolateral including central metaphyseal involvement), with only the posterior segment surviving as the 'viable island'; head-at-risk signs (calcification lateral to epiphysis, Gage's sign, horizontal physis, lateral subluxation, diffuse metaphyseal reaction) are typically present. Group IV — total head involvement. Groups I–II are low risk; III–IV are high risk and may require containment treatment.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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