What is the best X-ray (X-ray) view to assess knee valgus?

Best X-ray View to Assess Knee Valgus

For assessing knee valgus deformity, a standing full-length hip-to-ankle radiograph is the gold standard, as it alone provides accurate information on the weight-bearing mechanical axis necessary to evaluate lower limb malalignment. 1, 2

Primary Imaging Approach

Full-Length Hip-to-Ankle Radiograph (Long-Leg View)

• This is the definitive study for valgus assessment because it captures the entire mechanical axis from hip to ankle, which is essential for measuring the true degree of valgus deformity 1, 2
• Must be obtained in standing (weight-bearing) position to accurately reflect functional alignment under load 1, 2
• Provides comprehensive evaluation of the mechanical axis in patients with suspected lower limb malalignment 1

Standard Standing AP Knee Radiograph

• Can serve as a valid alternative for determining coronal plane alignment at the knee joint itself, but does not provide information about the overall mechanical axis 1, 2
• Should be obtained with 10° of internal rotation to improve interpretation of varus and valgus alignment compared to neutral positioning 1, 2
• Useful for follow-up after a baseline hip-to-ankle radiograph has been established 1

Optimal Imaging Protocol

For Initial Assessment of Valgus Deformity

1. Standing full-length hip-to-ankle radiograph as the primary study 1, 2
2. Standing AP knee view with 10° internal rotation for detailed joint assessment 1, 2
3. Standing lateral view for complete evaluation 1, 2

For Valgus Osteoarthritis Specifically

• Add a standing posterior-anterior (PA) flexed view (tunnel view), which is superior to standard AP views for detecting lateral compartment osteoarthritis in valgus knees 3
• The PA-flexed view significantly improves detection of joint space narrowing in patients with up to 15 degrees of valgus deformity 3
• This view is particularly valuable because valgus OA typically begins with cartilage degeneration along the posterior aspect of the lateral femoral condyle, which is poorly visualized on standard AP radiographs 3

Clinical Pitfalls to Avoid

• Do not rely on standard AP knee radiographs alone for valgus assessment—they cannot accurately measure the mechanical axis 1
• Avoid non-weight-bearing radiographs, as they fail to demonstrate true functional alignment under physiologic load 1, 2
• Do not obtain radiographs in neutral rotation when assessing valgus/varus alignment; 10° internal rotation significantly improves accuracy 1, 2
• For valgus OA, standard AP views underestimate disease severity in 62.4% of cases compared to PA-flexed views 3

Follow-Up Strategy

After establishing baseline alignment with a full-length hip-to-ankle radiograph, subsequent monitoring can utilize targeted standing AP knee radiographs with 10° internal rotation 1, though serial full-length films remain the gold standard for tracking progression of valgus deformity over time 1, 2.