## Why Trochlear dysplasia with reduced sulcus angle predisposing to patellar instability is right Trochlear dysplasia is a well-established anatomical abnormality of the femoral condyles and trochlea (structure **B**) that directly predisposes to patellar instability and recurrent dislocation. The flattened or dysplastic trochlear groove fails to provide adequate medial containment of the patella during knee flexion and extension, allowing lateral displacement. This is a key radiological finding on lateral knee X-rays and is a primary structural cause of patellar instability in adolescent athletes. (Maheshwari 10e) ## Why each distractor is wrong - **Medial femoral condyle hypoplasia causing lateral patellar tracking**: While femoral condyle anatomy matters, isolated medial condyle hypoplasia is not the classic association with patellar instability. Trochlear dysplasia (affecting the groove itself, not just one condyle) is the pathognomonic femoral abnormality. - **Femoral anteversion leading to internal rotation of the knee**: Femoral anteversion is a proximal femoral deformity, not a feature of the femoral condyles and trochlea. It affects hip rotation, not the direct trochlear anatomy shown in structure **B**. - **Increased Q-angle from femoral valgus deformity**: While valgus deformity can increase Q-angle and contribute to patellar tracking problems, this is a mechanical consequence of overall femoral alignment, not the specific anatomical abnormality of the trochlea itself visible on the lateral X-ray. **High-Yield:** Trochlear dysplasia = flattened/absent trochlear groove on lateral X-ray = patellar instability in adolescents; always assess sulcus angle and trochlear depth in recurrent dislocation. [cite:Maheshwari 10e — Knee X-ray landmarks: Femoral Condyles–Trochlear Dysplasia association with Patellar Instability]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.