A 7-year-old child is brought to the pediatric clinic by their parents who report that the child has been limping for the past 2 weeks and complaining of hip pain. Which assessment finding would be most characteristic of Legg-Calvé-Perthes disease?

Limited internal rotation and abduction of the hip are characteristic due to avascular necrosis of the femoral head causing joint stiffness. Other options like severe acute pain or visible deformity are more typical of acute conditions like fractures or septic arthritis.

Understanding the Clinical Presentation of Legg-Calvé-Perthes Disease

The hallmark of Legg-Calvé-Perthes disease (LCPD) is an insidious onset of symptoms stemming from idiopathic avascular necrosis of the femoral head, most common in children between the ages of 5 and 7 ^[1]. Because the ischemia and subsequent bone remodeling occur gradually, the presentation is typically chronic and progressive rather than acute. The child in the scenario has been limping for 2 weeks with hip pain, which aligns with the classic prodromal phase of the condition.

When assessing a child with suspected LCPD, the physical examination focuses on identifying the mechanical consequences of a softening and potentially collapsing femoral head. The condition leads to synovitis and muscle spasm, which create a characteristic pattern of restricted movement. The most pathognomonic finding is a limitation in internal rotation and abduction of the affected hip. This occurs because the inflamed synovium and the deformed femoral head physically block these specific ranges of motion. As the hip is flexed and moved into abduction, the flattened or fragmented femoral head impinges on the acetabular rim, causing pain and a hard end-feel that limits further movement.

Let’s analyze why the other options are less characteristic of LCPD:

- Severe acute pain with inability to bear weight is more indicative of an acute process such as septic arthritis, a fracture, or transient synovitis. LCPD typically presents with a gradual onset of limp and mild, intermittent pain that may be referred to the knee or thigh, rather than a sudden, incapacitating event.
- Visible deformity of the affected hip joint is a late finding. In the early stages of LCPD, there is no grossly visible deformity. Obvious deformities, such as a leg-length discrepancy or a prominent greater trochanter, only develop over months to years as the femoral head collapses and remodels.
- Swelling and warmth over the hip joint are cardinal signs of acute inflammation or infection. The hip joint is deep, and while LCPD involves an inflammatory component, visible superficial swelling and warmth are rare. These findings should immediately raise suspicion for septic arthritis, which is a medical emergency requiring prompt diagnosis and intervention.

In clinical practice, the diagnostic process is supported by imaging. Frog-leg lateral X-rays are essential for visualizing the femoral head and are a cornerstone of diagnosis, though early-stage LCPD may show only subtle changes on plain radiographs . The modified Waldenström staging system, which relies on these radiographic views, helps guide management by classifying the disease stage . Given that LCPD classically affects children aged 2-14 years, with a peak incidence around ages 5-7, a thorough history and a focused physical exam assessing for limited internal rotation and abduction are critical for early identification and referral [1,4].