Normal Sulcus Angle Size on Radiography | Knee
The sulcus angle is a radiographic measurement of the trochlear groove depth, defined as the angle formed at the deepest point of the femoral trochlea between its medial and lateral facets on a sunrise (axial) view. Accurate measurement is clinically important because trochlear dysplasia — characterized by a shallow or flattened groove — is a major predisposing factor for recurrent patellar dislocation and anterior knee pain.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Sunrise | 126-150¡ |
Clinical Significance
A normal sulcus angle ranges from 126° to 150° on the sunrise radiographic projection. A smaller angle reflects a deeper, more constraining trochlear groove, which provides greater inherent patellar stability. Conversely, a sulcus angle exceeding 150° indicates a shallow or flattened trochlea and is associated with trochlear dysplasia, a well-established risk factor for patellar maltracking and instability.
When the sulcus angle is elevated, clinicians should correlate with patient symptoms and additional imaging to characterize the degree of dysplasia. Trochlear dysplasia is commonly graded using the Dejour classification, and an abnormal sulcus angle may prompt surgical consideration such as trochleoplasty or tibial tubercle osteotomy in refractory cases.
- Recurrent patellar dislocation or subluxation
- Trochlear dysplasia (Dejour types A–D)
- Patellofemoral pain syndrome
- Post-traumatic trochlear remodeling
- Generalized ligamentous laxity with patellar hypermobility
Reference: Sanchis-Alfonso V. Anterior Knee Pain and Patellar Instability. Springer. (2011).
Imaging Notes
The sulcus angle is measured on the sunrise (axial) radiographic view, typically obtained with the knee flexed at 20–45°. The angle is constructed by drawing lines from the deepest point of the trochlear sulcus to the peaks of the medial and lateral femoral condyles. Consistent knee flexion angle between patients is important, as increasing flexion tends to deepen the apparent sulcus, potentially normalizing a dysplastic groove and underestimating pathology.
When radiographic assessment is equivocal, CT or MRI at low flexion angles (0–30°) provides superior cross-sectional delineation of trochlear morphology and allows additional measurements such as the trochlear depth and trochlear facet asymmetry to be assessed concurrently.