A 12-year-old obese boy presents with limp and referred knee pain for 2 months. Examination shows limited internal rotation of the right hip. X-ray pelvis shows posterior and medial displacement of the right femoral epiphysis relative to the metaphysis. In Slipped Capital Femoral Epiphysis (SCFE), the epiphysis is classified as 'unstable' when:
- A The epiphysis has slipped more than 50% of the femoral neck width
- B The patient is unable to bear weight regardless of the duration of symptoms ✓
- C The slip is acute-on-chronic in presentation
- D The slip angle is >30° on lateral X-ray
Correct answer: B. The patient is unable to bear weight regardless of the duration of symptoms
Explanation
The Loder classification divides SCFE into stable (able to bear weight, with or without crutches) and unstable (unable to bear weight regardless of duration). Unstable SCFE carries a dramatically higher risk of avascular necrosis (~47%) compared to stable SCFE (~0%). This classification is more clinically relevant than degree of slip for predicting AVN risk and urgency of treatment. Unstable SCFE requires urgent surgical stabilization (in situ pinning within 24 hours). The Southwick angle classifies severity by degree of slip but does not determine stability.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.