Best X-ray Series for Knee Evaluation
The best x-ray series for evaluating the knee consists of standing anteroposterior (AP), lateral, and tangential axial (sunrise/Merchant) views of the patellofemoral joint, with additional weight-bearing tunnel view recommended for comprehensive assessment. 1, 2
Standard Knee Radiographic Series
Primary Views (Essential)
- Standing Anteroposterior (AP) view: Evaluates tibiofemoral joint space, alignment, and bony structures
- Lateral view: Assesses patellar position, joint effusion, and posterior structures
- Tangential axial view (sunrise/Merchant): Examines patellofemoral joint and patellar tracking
Additional Recommended Views
- Weight-bearing tunnel view: Improves detection of intercondylar notch pathology, tibial spine osteophytes, and early arthritis changes not visible on standard AP 3, 4
- Standing long-leg (hip-to-ankle) view: Provides optimal assessment of overall limb alignment; particularly valuable as a baseline assessment 1
Clinical Scenarios and View Selection
For Routine Knee Evaluation
- The combination of standing AP, lateral, and tangential axial views provides comprehensive assessment of all knee compartments 1
- Adding the tunnel view significantly increases detection of joint space narrowing in both lateral (p<0.001) and medial (p=0.006) compartments compared to AP view alone 3
For Alignment Assessment
- Standing AP knee radiograph is a valid alternative to hip-to-ankle radiograph for determining coronal plane alignment at the knee 1
- After acquiring a baseline hip-to-ankle radiograph, further follow-up can be based on targeted knee radiographs 1
For Post-Arthroplasty Evaluation
- Standing AP and lateral views with tangential axial view of patellofemoral joint 1
- Some practitioners also use standing long-leg views to provide optimal assessment of alignment 1
Technical Considerations
- AP views obtained in 10° of internal rotation improve interpretation of varus and valgus alignment compared to neutral AP views 1
- Weight-bearing views are essential for accurate assessment of joint space narrowing 1
- For osteoarthritis evaluation, the weight-bearing tunnel view combined with weight-bearing AP significantly increases detection of:
- Medial subchondral cysts (p=0.022)
- Sclerosis of lateral tibial plateau (p=0.041)
- Moderate-to-large osteophytes in medial compartment (p=0.012) 3
Common Pitfalls to Avoid
- Ordering MRI before appropriate radiographs 2
- Failing to obtain weight-bearing views when evaluating for osteoarthritis 1
- Missing intercondylar notch and tibial spine pathology by omitting tunnel views 4
- Inadequate positioning affecting visualization of periprosthetic lucencies 1
By following this comprehensive radiographic protocol, clinicians can maximize diagnostic yield while minimizing unnecessary radiation exposure and healthcare costs.