A 14-year-old male who is overweight presents with left knee and anteromedial thigh pain for the past month. The knee X-ray is normal. The most likely diagnosis is?

• A. Genu valgum
• B. Legg-Calve-Perthes disease
• C. Osgood-Schlatter disease
• D. Slipped capital femoral epiphysis

Answer: (A)

When a teenage patient has knee pain with a normal knee radiograph, think about alignment and overuse rather than acute joint disease. Genu valgum, or knock-knee, is a structural alignment issue where the knees angle inward. This abnormal loading of the medial knee compartment can cause knee pain during activity and, due to compensatory changes in gait and muscle use, discomfort that can be felt higher up in the anteromedial thigh. The absence of knee x-ray findings fits a mechanical problem rather than an intra-articular process or a hip disorder.

In this setting you’d expect to find a noticeable valgus alignment on exam with an increased Q-angle. Management focuses on weight control and targeted physical therapy to strengthen hip abductors and thigh muscles, which can improve alinement and reduce pain; many patients improve as growth occurs, though persistent deformity may require braces or, rarely, surgical consideration.

Legg-Calve-Perthes disease and slipped capital femoral epiphysis primarily involve the hip and typically present with hip or groin pain (SCFE can cause knee pain but usually has signs of hip pathology and gait changes), while Osgood-Schlatter disease causes anterior knee pain at the tibial tubercle. The distribution and the normal knee x-ray make genu valgum the best-fitting explanation in this scenario.