A previously healthy adolescent with intermittent right anterior thigh pain and limp; 25th percentile height and weight; limited abduction and internal rotation of the hip. What is the most likely diagnosis?

• A. Avascular necrosis of the femoral head (Legg-Calvé-Perthes disease)
• B. Slipped Capital Femoral Epiphysis
• C. Septic arthritis
• D. Osteomyelitis

Answer: (C)

In an adolescent with hip or referred thigh pain and a limp, a key clue is loss of hip motion, especially internal rotation, with an otherwise nonacute course. This pattern points to a problem at the proximal femur or femoral head rather than an acute joint infection. Slipped capital femoral epiphysis is the classic diagnosis in this age group: a physis that has slipped allows the femoral head to sit out of place, leading to limited internal rotation and abduction, and the pain is often felt in the anterior thigh or groin with a limp. The presentation is typically subacute rather than rapidly progressive, and systemic symptoms are usually absent.

Avascular necrosis (Legg-Calvé-Perthes) tends to occur in younger children (roughly ages 4–8) and presents with a more insidious limp with often more longstanding changes in gait and radiographs showing femoral head changes over time. Septic arthritis would present with an acute onset of severe hip pain, fever, and systemic toxicity, often with a marked inability to bear weight and joint swelling. Osteomyelitis would involve bone infection with fever and focal bone pain, again usually more acute and with systemic signs.

Thus the most likely diagnosis in this adolescent with intermittent anterior thigh pain, limp, and limited hip motion is slipped capital femoral epiphysis.