On an anteroposterior pelvic radiograph of a 12-year-old boy, a line drawn along the superior aspect of the femoral neck passes above and does not intersect the capital femoral epiphysis on the left side. This finding indicates:

• A Normal anatomy of the left hip
• B Legg-Calve-Perthes disease on the left side
• C Developmental dysplasia of the left hip
• D Slipped capital femoral epiphysis on the left side ✓

Explanation

The line described is Klein's line. Normally it intersects the lateral portion of the capital femoral epiphysis. When the epiphysis has slipped posteroinferiorly it falls below the line, so the line misses the epiphysis; this is Trethowan's sign and is diagnostic of a slipped capital femoral epiphysis, including mild slips that are otherwise subtle. Shenton's line disruption suggests dysplasia or dislocation, while Perthes is suggested by epiphyseal sclerosis and fragmentation instead.

Reference: Campbell's Operative Orthopaedics, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.