LATERAL TROCHLEAR INCLINATION IN CHILDREN AND ADOLESCENTS: MODIFIED MEASUREMENT TECHNIQUE TO CHARACTERIZE PATELLAR INSTABILITY

Patellar instability (PI) is relatively rare but occurs most often in younger patients with underlying pathoanatomy. Trochlear dysplasia (TD) is one of many identified PI risk factors, but consensus is lacking on ideal radiographic measurements. The Dejour classification of TD on lateral radiographs is widely accepted but has suboptimal intra and interrater reliability and does not allow quantification of TD. Lateral trochlear inclination (LTI) measured on the most proximal axial magnetic resonance image (MRI) of the trochlear chondral surface is another described measurement of TD. LTI has historically been described with reference to the posterior aspect of the femur at the same axial level at which the proximal trochlea is measured. However, given the transitional anatomy of the distal femur, the LTI may be better represented by referencing the axis of the fully formed posterior femoral condyles. The posterior condyles represent a true axis of rotation that serves as an internal reference for knee motion and is clearly visible on MRI. We hypothesized that modified LTI measurements (LTI) referencing the posterior condylar axis would differ from the apparent LTI (ALTI) in a pediatric and adolescent population. We also hypothesized that the LTI would have stronger intra and inter reliability than the ALTI measurement and Dejour classification. Lastly, we hypothesized that the most proximal level of the trochlea would adequately represent overall proximal trochlear morphology. This is clinically relevant because dysplasia is most severe on the proximal trochlea and normalizes distally towards the intercondylar notch