= SLIPPED CAPITAL FEMORAL EPIPHYSIS

= atraumatic fracture through hypertrophic zone of physeal plate

Frequency: 2÷100,000 people

Etiology: growth spurt, renal osteodystrophy, rickets, childhood irradiation, growth hormone therapy, trauma (Salter-Harris type I epiphyseal injury)

Pathogenesis: widening of physeal plate during growth spurt + change in orientation of physis from horizontal to oblique increases shear forces

Mean age: 13 years for often overweight boys (range, 8–17 years), 11 years for girls; M÷F = 3÷1; Black >White

Associated with:

1. malnutrition, endocrine abnormality, developmental dysplasia of hip (during adolescence)
2. delayed skeletal maturation (after adolescence)

• hip pain (50%) / knee pain (25%) for 2–3 weeks

Location: usually unilateral; bilateral in 20–37% (at initial presentation in 9–18%)

• widening of epiphyseal growth plate (preslip phase):
  • irregularity + blurring of physeal physis
  • demineralization of neck metaphysis
• posteromedial displacement of head (acute slip):
  • decrease in neck-shaft angle with alignment change of growth plate to a more vertical orientation
  • line of Klein (= line drawn along superior edge of femoral neck) fails to intersect the femoral head
  • epiphysis appears smaller ← posterior slippage: early slips are best seen on cross-table LAT view
    CAVE: positioning into a frog leg view may cause further displacement
• sclerosis + irregularity of widened physis (chronic slip):
  • metaphyseal “blanch” sign = area of increased opacity in proximal part of metaphysis (healing response)

Grading (based on femoral head position):

• mild = displaced by <⅓ of metaphyseal diameter
• moderate = displaced by ⅓/⅔ of diameter
• severe = displaced by >⅔ of metaphyseal diameter

Cx:

1. Chondrolysis = acute cartilage necrosis (7–10%)
   = rapid loss of >50% of thickness of cartilage
   • joint space <3 mm
2. Avascular necrosis of femoral head (10–15%): risk increases with advanced degree of slip, delayed surgery for acute slip, anterior pin placement, large number of fixation pins, subcapital osteotomy
3. Pistol-grip deformity = broadening + shortening of femoral neck in varus deformity
4. Degenerative osteoarthritis (90%)
5. Limb-length discrepancy ← premature physeal closure

Rx:

1. limitation of activity
2. prophylactic pinning
3. osteotomy

• Attempted reductions increase risk of AVN!