Overcoming Limitations in Tibial Tubercle-Trochlear Groove Distance Measurement: A Study of Its Reproducibility and Reliability in High-Grade Trochlear Dysplasia.

BACKGROUND: In cases of high-grade trochlear dysplasia, identifying the reference point of the trochlear groove can be challenging when measuring the tibial tubercle-trochlear groove (TT-TG) distance. PURPOSE/HYPOTHESIS: The purpose of this study is to evaluate the reliability of TT-TG measurements obtained at different trochlear reference levels. It was hypothesized that TT-TG measurements would remain feasible even in cases of high-grade trochlear dysplasia when alternative trochlear reference levels are used. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A retrospective analysis of magnetic resonance imaging scans from patients presenting with patellar instability between 2019 and 2023 was performed. For each patient, the TT-TG distance was measured at 3 levels on axial magnetic resonance imaging: high (hTT-TG), middle (mTT-TG), and low (lTT-TG). The TT-posterior cruciate ligament (TT-PCL) distance was also measured. TT-TG values were compared across the 3 reference levels. Inter- and intraobserver reliability were assessed using the intraclass correlation coefficient (ICC). RESULTS: A total of 136 knees were included, of which 64% presented with high-grade trochlear dysplasia (37 Dejour type B and 50 type D). No statistically significant differences were observed between TT-TG measurements obtained at the 3 reference levels. The hTT-TG could be measured in 115 of 136 knees. Among the 21 knees in which hTT-TG could not be measured, 16 were associated with Dejour type D dysplasia, 1 with type C, 3 with type B, and 1 with type A dysplasia. The lTT-TG was measurable in all patients. Interobserver ICC values were good and excellent for lTT-TG, mTT-TG, and hTT-TG (0.877, 0.929, and 0.892, respectively), and intraobserver ICC values were also excellent (0.976, 0.976, and 0.954, respectively). The interobserver reliability for TT-PCL was moderate (ICC, 0.606), whereas intraobserver reliability remained excellent (ICC, 0.925). CONCLUSION: TT-TG measurements remained feasible and reproducible in this cohort of patients with patellar instability, including a high proportion of high-grade trochlear dysplasia, when a slightly more distal trochlear reference level was used. TT-PCL remains a potential alternative although its interobserver reliability was lower than that of TT-TG in the present study.