A 6-year-old boy is brought to the clinic because of a dull, aching pain in his right groin and thigh that has been present for the past two months. His parents report that the pain is worse after his soccer practice and that he has developed a persistent limp. He has no history of trauma, fever, or recent viral illness. On physical examination, he has limited internal rotation and abduction of the right hip. There is mild atrophy of the right proximal thigh muscles. A Trendelenburg sign is positive on the right. Plain radiography of the pelvis reveals a small, fragmented, and slightly flattened right femoral head with increased radiodensity.
Which of the following is the most likely underlying pathophysiology of this patient's condition?
The correct answer is:
B) Avascular necrosis of the femoral head
The patient is presenting with Legg-Calvé-Perthes disease (LCPD), which is idiopathic avascular necrosis of the femoral head. It typically affects children between the ages of 4 and 10 years and is much more common in boys. The classic presentation is an insidious onset of hip, groin, or knee pain and an antalgic limp. Unlike slipped capital femoral epiphysis (SCFE), which occurs in older, often obese adolescents, LCPD occurs in younger, often active children. The pathophysiology involves a temporary interruption of blood supply to the capital femoral epiphysis, leading to bone necrosis, followed by a period of revascularization and bone remodeling. On X-ray, this manifests as a "flattened" or fragmented femoral head.
Answer choice A: Autoimmune destruction of the synovial lining, is incorrect. This describes juvenile idiopathic arthritis (JIA). While JIA can cause hip pain, it typically presents with systemic symptoms like fever or rash, involvement of multiple joints, and elevated inflammatory markers.
Answer choice C: Displacement of the epiphysis through the physis, is incorrect. This describes slipped capital femoral epiphysis (SCFE). As discussed previously, SCFE typically affects older, heavier adolescents and shows a "scoop of ice cream slipping off a cone" appearance on X-ray.
Answer choice D: Infection of the joint space, is incorrect. This describes septic arthritis. Septic arthritis is an acute emergency characterized by high fever, refusal to bear weight, and irritable hip where any movement is extremely painful.
Answer choice E: Inflammation of the tibial tuberosity, is incorrect. This describes Osgood-Schlatter disease, which causes pain specifically at the anterior knee (tibial tubercle) in active adolescents, not the hip.
Key Learning Point
Legg-Calvé-Perthes disease is idiopathic avascular necrosis of the femoral head in children, typically ages 4–10 years. It presents with an insidious limp and limited hip abduction/internal rotation. Management is usually conservative with observation and bracing to maintain the femoral head within the acetabulum during the remodeling process.
