A 12-year-old obese boy presents with a 3-week history of right hip pain radiating to the knee and a limp. He is afebrile. On examination, right hip external rotation is noted with flexion, and passive internal rotation is restricted and painful. X-ray (AP and frog-leg lateral) shows posterior inferior displacement of the femoral head epiphysis. Loder classification of this injury is important. An 'unstable' SCFE is defined as:

• A Preslip stage — abnormal widening of the physis on X-ray without displacement
• B Slip angle >30° (Southwick angle) on frog-leg lateral
• C Bilateral SCFE detected on contralateral X-ray
• D Inability to bear weight on the affected limb regardless of slip angle ✓

Explanation

The Loder classification of SCFE is based on ability to bear weight: Stable — child can bear weight (with or without crutches); Unstable — child CANNOT bear weight on the affected limb regardless of slip magnitude. Unstable SCFE carries a 25–50% risk of avascular necrosis (vs <5% in stable SCFE) because the acute displacement interrupts the posterior superior retinacular vessels. Management of unstable SCFE requires emergency surgical stabilisation (in situ pinning with single cannulated screw) within 24 hours, after gentle positioning (not forceful reduction, which risks AVN). Slip angle and bilateral disease are not components of the Loder classification.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.