A 13-year-old boy sustains a minor fall while playing football and now has severe left hip pain. He is completely unable to walk, even with crutch support. Radiographs show a slipped capital femoral epiphysis. How is this slip classified and what is its major implication?

• A Stable slip, high risk of chondrolysis
• B Pre-slip, high risk of contralateral slip only
• C Acute-on-chronic slip, high risk of malunion
• D Unstable slip, high risk of avascular necrosis of the femoral head ✓

Explanation

Loder classified slips by stability: an unstable slip means the patient cannot bear weight even with crutches, while a stable slip allows weight bearing. Unstable slips carry a risk of avascular necrosis approaching 40 to 50 percent because the retinacular vessels supplying the epiphysis are disrupted, whereas stable slips have an avascular necrosis risk below 1 percent. Stability, not duration of symptoms, drives this prognostic difference.

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

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