Normal Patellar Tilt Angle: Radiography, CT & MRI
Patellar tilt refers to the angular orientation of the patella relative to the femoral trochlea in the axial plane, describing whether the patella tilts laterally or medially about its long axis. Accurate measurement of patellar tilt is essential for evaluating anterior knee pain, patellofemoral instability, and malalignment syndromes. It guides both conservative and surgical management decisions in patients with patellofemoral disorders.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Sunrise | 20¡ |
Clinical Significance
A normal patellar tilt angle of 20° is established on the sunrise (axial) view. Lateral patellar tilt — where the lateral patellar facet tilts inferiorly relative to the medial facet — is the most clinically relevant abnormality. Tilt exceeding 20° is generally considered abnormal and may indicate lateral retinacular tightness, trochlear dysplasia, or vastus medialis oblique weakness.
Excessive lateral tilt is associated with abnormal lateral facet loading, accelerated cartilage wear, and anterior knee pain. It frequently coexists with other malalignment parameters such as increased tibial tubercle–trochlear groove (TT-TG) distance and patellar alta. Isolated tilt without subluxation can still produce symptomatic patellofemoral syndrome and chondromalacia.
- Lateral retinacular tightness — most common cause of increased lateral tilt
- Trochlear dysplasia — shallow trochlea fails to constrain patellar orientation
- Patellofemoral instability / recurrent dislocation
- Chondromalacia patellae — lateral facet overload pattern
- Post-traumatic malalignment — retinacular scarring after acute dislocation
Reference: Robinson P. Essential Radiology for Sports Medicine. Springer Science+Business Media. (2010).
Imaging Notes
On radiography, the sunrise (Merchant or Laurin) axial projection at 30–45° of knee flexion is standard for assessing patellar tilt. The tilt angle is measured between a line along the lateral patellar facet and a line connecting the femoral condyle peaks. Positioning consistency is critical, as knee flexion angle significantly influences the apparent tilt.
On CT and MRI, axial images through the patellofemoral joint provide the most reliable and reproducible measurements, with MRI having the added advantage of direct cartilage assessment. A reference line connecting the posterior femoral condyles serves as the baseline; the patellar tilt angle is then measured to the lateral patellar facet line. MRI is preferred when concurrent evaluation of the retinaculum, trochlear cartilage, or medial patellofemoral ligament (MPFL) integrity is required.