Validating the Role of Tibial Tubercle-Posterior Cruciate Ligament Distance and Tibial Tubercle-Trochlear Groove Distance Measured by Magnetic Resonance Imaging in Patients With Patellar Dislocation: A Diagnostic Study

Purpose: To (1) compare these parameters between patients with patellar dislocation and healthy individuals on magnetic resonance imaging measurements, (2) validate the diagnostic capacity of the tibial tubercle-posterior cruciate ligament (TT-PCL) distance and tibial tubercleetrochlear groove (TT-TG) distance, (3) define the pathologic threshold values of these parameters for tibial tubercle osteotomy indication, and (4) compare these values with those of previous studies. Methods: Seventy patients with patellar dislocation and 70 healthy volunteers were identified. The inter- and intra-observer reliability values were determined using Bland-Altman analysis and the intraclass correlation coefficient (ICC). The diagnostic capacity of the parameters was evaluated using receiver operating characteristic curves and the area under the receiver operating characteristic curve. The data of the control group were used to determine the pathologic threshold values of the measurements. Logistic regression analysis was performed with these pathologic threshold values. Results: Significant differences in the TT-PCL distance (P = .01) and TT-TG distance ( P < .001) were found between the study group (21.48 +/- 3.18 and 12.91 +/- 3.80, respectively) and the control group (20.07 +/- 2.99 and 8.46 +/- 3.16, respectively). Both the TT-PCL distance and TT-TG distance had excellent inter- and intraobserver agreement, with inter-ICCs >0.915 and intra-ICCs >0.932, respectively. However, the TT-TG distance had a higher area under the receiver operating characteristic curve than did the TT-PCL distance (0.820 vs 0.627). The pathologic threshold value of the TT-PCL distance was 24.76 mm. The pathologic threshold value of the TT-TG distance was 13.64 mm. Subjects with a TT-TG distance of >13.64 mm had a greater risk for patellar dislocation, with an odds ratio of 14.02 (95% confidence interval 4.00-49.08, P < .001). Conclusions: Both the TT-PCL distance and TT-TG distance can be measured reliably by magnetic resonance imaging; however, the TT-TG distance has a better diagnostic capacity than does the TT-PCL distance.

Automated summary

This study compared the parameters between patients with patellar dislocation and healthy individuals on MRI measurements, validating the diagnostic capacity of TT-PCL distance and TT-TG distance. The TT-TG distance had better diagnostic capacity than the TT-PCL distance, and a pathologic threshold value of 13.64 mm was determined for TT-TG distance.