An overweight 13-year-old boy presents with limp and referred knee pain. On the frog-leg lateral pelvic radiograph, a line drawn along the superior margin of the femoral neck fails to intersect any part of the capital femoral epiphysis on the left side. The most likely diagnosis is:

• A Developmental dysplasia of the hip
• B Legg-Calve-Perthes disease
• C Slipped capital femoral epiphysis ✓
• D Transient synovitis

Explanation

Klein's line drawn along the superior femoral neck should normally intersect the lateral third or more of the capital femoral epiphysis. Failure of the line to intersect the epiphysis indicates superior displacement of the epiphysis relative to the neck, which is slipped capital femoral epiphysis. This typically affects overweight adolescent boys and classically presents with hip or referred knee pain. In Legg-Calve-Perthes disease the abnormality is fragmentation and sclerosis of the epiphysis itself, while developmental dysplasia is assessed by Shenton's line and acetabular indices.

Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.