Best X-rays for Patellar Tracking Assessment
For assessing patellar tracking, axial (tangential) radiographs are the most effective X-ray views, particularly when obtained in a weight-bearing position to better evaluate patellofemoral kinematics. 1
Recommended Radiographic Views for Patellar Tracking
- Axial (tangential) radiographs: These views demonstrate the degree of patellar tilt or subluxation and are the primary radiographic method for assessing patellar tracking 1
- Weight-bearing axial radiographs: Provide superior assessment of patellofemoral kinematics compared to non-weight-bearing views 1
- Standing anteroposterior (AP) and lateral views: Should be included as part of a complete assessment of patellar position and alignment 1
Optimal Positioning for Accurate Assessment
- Weight-bearing position: Enhances the evaluation of true functional patellar tracking during load-bearing conditions 1
- Multiple flexion angles: Consider obtaining axial views at different degrees of knee flexion (particularly at 20-30 degrees) as patellar tracking abnormalities may be more apparent at specific angles 2, 3
- 10 degrees of internal rotation: When obtaining AP views, this position improves the interpretation of varus and valgus alignment compared to neutral AP views 1
Clinical Applications and Considerations
- Patellofemoral instability: Axial radiographs are particularly useful for evaluating patellar subluxation, tilt, and dislocation 1
- Post-TKA assessment: Axial views are essential for evaluating patellar complications after total knee arthroplasty, including component malposition 1
- Limitation of static imaging: Standard radiographs provide only static assessment of patellar position rather than dynamic tracking 4, 5
Important Caveats
- Static vs. dynamic assessment: X-rays provide only static snapshots of patellar position; abnormal tracking may be missed if it occurs dynamically during movement 4, 2
- Knee flexion angle matters: Patellar tracking abnormalities may only be apparent at specific flexion angles (often early in flexion), so imaging at multiple angles may be necessary 2, 3
- Merchant views (45° flexion) may miss abnormalities: Some patellar tracking issues are more evident at lesser degrees of flexion (30° or less), making standard Merchant views potentially inadequate for complete assessment 2
- Consider advanced imaging: For complex cases or when X-rays are inconclusive, CT or MRI may provide more detailed information about patellar tracking, particularly regarding component rotation in post-TKA patients 1
When to Consider Advanced Imaging
- CT scanning: Most commonly used for measuring axial malrotation of knee prostheses and can provide more detailed assessment of patellar tracking when X-rays are inconclusive 1
- MRI with metal artifact reduction: Can be useful for assessing patellar complications in post-TKA patients when radiographs are inconclusive 1
- Kinematic MRI: May be considered for detailed evaluation of dynamic patellar tracking in complex cases 2