The diagnostic value of TT-TG and TT-ME distances in the assessment of patellofemoral instability

Abstract

Purpose: This study aims to evaluate the application value of the tibial tubercle-trochlear groove distance (TT-TG distance) and tibial tubercle-midepicondyle distance (TT-ME distance) on CT images in patellofemoral instability, and further investigate the association between knee joint rotation angles and patellofemoral instability.

Methods: We retrospectively analyzed CT image data of 59 patients with patellar dislocation (case group) and 39 normal knee joints (control group). We measured the TT-TG distance, TT-ME distance, and knee joint rotation angle (KJRA) of both groups, and the related indicators were analyzed using single-factor/multi-factor binary logistic stepwise regression analysis. Two senior radiologists were assigned to assess the inter-rater reliability. Interclass correlation coefficients (ICC) were calculated. Finally, we used receiver operating characteristic (ROC) curves to compare the diagnostic efficiency of these indicators in patellofemoral instability.

Results: The results found significant differences between both groups in terms of TT-TG distance, TT-ME distance, KJRA angle, age, location, and gender (P < 0.05). In terms of inter-rater reliability, TT-TG distance and TT-ME distance ratios showed an excellent correlation between observers (TT-TG inter-rater ICC 0.969, TT-ME inter-rater ICC 0.955). Univariate logistic regression analysis indicated that except for location and gender, all other factors significantly affected patellofemoral instability (P < 0.05). The multivariate logistic regression analysis revealed that the TT-ME distance, age, and KJRA angle were statistically significant factors related to patellofemoral instability, with TT-ME distance being a risk factor for patellofemoral instability (OR value 1.572, P value 0.000). Moreover, the ROC curve analysis demonstrated that the diagnostic capability of the TT-ME distance for detecting patellofemoral instability was higher than that of the TT-TG distance and KJRA (AUC were 0.912, 0.851, and 0.735, respectively).

Conclusion: The TT-ME distance, age, and knee joint rotation angle are factors that affect patellofemoral instability. The TT-ME distance has better diagnostic efficiency for patellofemoral instability compared to the TT-TG distance and knee joint rotation angle.

Keywords: Knee joint rotation angle; Patellofemoral instability; Tibial tubercle–midepicondyle distance; Tibial tubercle–trochlear groove distance.