Normal Femoral Intercondylar Sulcus Depth Size on Radiography
The femoral intercondylar sulcus, also known as the trochlear groove, is the central depression of the distal femoral trochlea that articulates with the patella. Its depth reflects the bony constraint available to resist lateral patellar displacement. Accurate measurement is clinically important in the evaluation of patellofemoral instability and recurrent patellar dislocation.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Sunrise | >5 mm |
Clinical Significance
A sulcus depth greater than 5 mm is considered normal on the sunrise (axial/skyline) radiographic view. Reduction in sulcus depth — a shallow or flat trochlea — is the hallmark of trochlear dysplasia, which is one of the most important anatomical risk factors for recurrent patellar instability. Trochlear dysplasia is classified by the Dejour system, with higher grades associated with progressively abnormal trochlear morphology including a crossing sign, supratrochlear spur, and double contour on lateral views.
A shallow sulcus diminishes the passive stabilizing force on the patella, predisposing patients to lateral patellar subluxation or dislocation, particularly during the early degrees of knee flexion when dynamic muscular stabilizers are least effective. Pitfalls include oblique positioning of the knee during the sunrise view, which can artificially alter the apparent sulcus depth and lead to misclassification.
- Trochlear dysplasia (Dejour grades A–D)
- Recurrent patellar instability / dislocation
- Patellofemoral pain syndrome
- Post-traumatic trochlear remodeling
- Generalized ligamentous laxity with multidirectional instability
Reference: Robinson P. Essential Radiology for Sports Medicine. Springer Science+Business Media. (2010).
Imaging Notes
Sulcus depth is measured on the sunrise (axial/skyline) radiographic view, typically obtained with the knee flexed to 30–45°. The measurement represents the perpendicular distance from the deepest point of the trochlear groove to a line connecting the medial and lateral femoral condyle peaks. Consistent knee flexion angle is essential, as increasing flexion tends to deepen the apparent groove due to progressive patellar engagement; standardizing the protocol to 30° of flexion is recommended for reproducibility.
When interpreting borderline values, correlation with the lateral radiograph for the crossing sign and with MRI for cartilaginous trochlear contour is advised, as plain radiography reflects only the osseous component of the groove.