Demystifying Tibial-Tuberosity Trochlear Groove Distance, the J-Sign and Trochlear Dysplasia: An Imaging Encomium

Abstract

Aims and objective: The purpose of our study was to examine the association of the clinical J-sign with trochlear dysplasia and TTTG distance in patients with symptomatic patellofemoral instability. Material and methods: After obtaining approval from the institutional review board (class: 8.1-16/47-2, Nr.: 02/21AG, April 11, 2017), in our retrospective cross-sectional review study, 2 raters mutually assessed the type of trochlear dysplasia and separately measured the TTTG distance at 4-week intervals using 2 methods (standard and by Nizi#) on static and dynamic CT-images of 55 knees (46 patients) with clinical record of J-sign and anterior knee pain. Statistical analysis: All reported P values were 2-tailed with a level of <0.05 indicating statistical significance. The associations between variables were analyzed with appropriate correlation coefficients (Pearson, rp, pointbiserial, rpb, and phi, r#). The Wilcoxon signed-rank test for paired samples was used to evaluate the differences between static and dynamic tibial tuberosity-trochlear groove. Conclusion: The clinical manifestation of the J-sign, considered a dynamic marker of patellofemoral instability, has been frequently associated with numerous conditions, such as trochlear dysplasia, higher values of the Q-angle, and lateralized tibial tuberosity, yet its fundamental cause remains unknown, and the diagnostic value uncertain.