A 6-year-old boy with hip pain has an AP pelvic radiograph showing a thin subchondral radiolucent line parallel to the articular surface of the capital epiphysis. What is this finding called and what does it represent?

• A Sagging rope sign; fibrous tissue across the old physis
• B Gage sign; osteoporosis of the metaphysis
• C Crescent sign; subchondral fracture of the necrotic epiphysis ✓
• D Waldenstrom sign; joint effusion displacing the fat pad

Explanation

The crescent sign is a subchondral fracture producing a linear lucency beneath the articular surface; it is virtually pathognomonic of Legg-Calve-Perthes disease and appears during the early fragmentation stage. The sagging rope sign is a dense band along the widened metaphysis seen in healed disease. Gage sign is a V-shaped osteoporotic defect at the lateral epiphysis and metaphysis, one of Catterall's head-at-risk signs, not a fracture line.

Reference: Tachdjian's Pediatric Orthopaedics, 5th ed.

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