Normal Lateral Trochlear Inclination Size on MRI
The lateral trochlear inclination (LTI) is the angle formed between the lateral trochlear facet and a posterior condylar reference line on axial MRI, reflecting the depth and slope of the lateral trochlear groove. Accurate measurement of LTI is clinically important because a shallow or flat trochlea predisposes the patella to lateral subluxation and recurrent instability. It serves as one of several MRI parameters used to evaluate trochlear dysplasia in patients with patellofemoral disorders.
Normal Reference Values
| Measurement |
|---|
| >11¡ |
Clinical Significance
A normal lateral trochlear inclination is defined as greater than 11°. Values at or below this threshold indicate a relatively flat lateral trochlear facet, consistent with trochlear dysplasia — a well-recognized anatomic risk factor for patellar instability. Trochlear dysplasia is graded using the Dejour classification, and a reduced LTI correlates with higher-grade dysplasia and increased risk of recurrent patellar dislocation.
When LTI is diminished, the lateral trochlear wall fails to provide adequate osseous restraint to lateral patellar translation, particularly in early knee flexion where ligamentous stabilizers are less effective. This measurement should always be interpreted alongside other patellofemoral indices such as the trochlear sulcus angle, tibial tubercle–trochlear groove (TT-TG) distance, and patellar tilt angle to guide surgical planning.
- Trochlear dysplasia (primary cause of reduced LTI)
- Recurrent patellar dislocation or subluxation
- Patellofemoral pain syndrome with structural instability
- Post-traumatic trochlear remodeling
- Osteochondral defects associated with chronic instability
Reference: Carrillon Y, Abidi H, Dejour D et al. Patellar instability: assessment on MR images by measuring the lateral trochlear inclination-initial experience. Radiology. 2000;216(2):582-5.
Imaging Notes
LTI is measured on axial MRI sequences through the proximal trochlea, ideally on proton density or T1-weighted images where cartilage and osseous landmarks are well delineated. The angle is drawn between a line along the subchondral surface of the lateral trochlear facet and a reference line connecting the posterior aspects of the femoral condyles. Consistent use of the posterior condylar line as the reference is critical for reproducibility. Slice selection should target the most proximal axial image at which both trochlear facets are simultaneously visible.
Cartilage-sensitive sequences (e.g., fat-suppressed proton density) improve delineation of the articular surface, which is particularly relevant in younger patients where ossification may be incomplete. Care should be taken to avoid oblique slices, as out-of-plane angulation can falsely alter the measured inclination angle.