What X-ray views are recommended for patella evaluation?

X-Ray Views for Patella Evaluation

For patellar imaging, obtain anteroposterior (AP) and lateral views of the knee, plus an axial (tangential) view of the patellofemoral joint—ideally performed in weight-bearing position. 1, 2

Standard Radiographic Protocol

The American College of Radiology recommends a three-view series for comprehensive patellar evaluation 1:

• AP view: Standard anteroposterior projection in weight-bearing position 1
• Lateral view: Weight-bearing lateral projection 1
• Axial (tangential) view: Also called "skyline" or "Merchant" view—this is the primary view for assessing patellar tracking, tilt, and subluxation 2

Why the Axial View Matters

The axial view is essential for detecting patellar pathology that other views miss. 2, 3

• Axial radiographs demonstrate the degree of patellar tilt or subluxation better than any other plain film view 2, 4
• Weight-bearing axial views provide superior assessment of patellofemoral kinematics compared to non-weight-bearing views 2, 5
• In patients with patellar dislocation, the lateral view showed 98% sensitivity while the axial view showed only 62% sensitivity—but combining both views provides optimal diagnostic accuracy 3

Critical Technical Point: Weight-Bearing Position

Obtain the axial view with the patient standing in a semi-squatted position (45° knee flexion) whenever possible. 5

• Weight-bearing axial views reveal patellofemoral tracking changes that are missed on standard non-weight-bearing views 5
• The standing position with muscle activation reproduces true in vivo patellofemoral kinematics 5
• Weight-bearing views show significantly reduced lateral tilt and subluxation compared to supine views, and better correlate with clinical symptoms 5

When Evaluating for Acute Trauma

For suspected patellar fractures following acute knee trauma 4:

• Start with minimum two views: AP and lateral 4
• Add the patellofemoral (axial) view to evaluate for patellar fractures and/or subluxation or dislocation 4
• Common pitfall: Recent evidence suggests the skyline view may not significantly increase fracture detection sensitivity (92.86% without skyline vs 97.86% with skyline, p=0.1), but guidelines still recommend it for comprehensive evaluation 6

Additional Technical Considerations

• For optimal AP views when assessing alignment: use 10° internal rotation to improve interpretation of varus and valgus alignment 1
• Ensure precise overlap of posterior femoral condyles on the lateral view to accurately assess patellar position 3
• The lateral view in full extension has 98% sensitivity for detecting prior patellar dislocation 3

When Plain Films Are Insufficient

If radiographs are inconclusive 4, 2:

• CT with metal artifact reduction: Best for detailed bone assessment and measuring component rotation in post-arthroplasty patients 4, 2
• MRI with metal artifact reduction: Useful for soft tissue injuries, cartilage damage, and bone marrow edema 2, 7