Middle patellar tendon to posterior cruciate ligament (PT-PCL) and normalized PT-PCL: New magnetic resonance indices for tibial tubercle position in patients with patellar instability.

Abstract

To demonstrate whether the distance between the middle point of the patellar tendon and posterior cruciate ligament (PT-PCL) calculated on a single axial MR image could be an alternative measure to tibial tubercle-PCL (TT-PCL) distance for TT lateralization without the need of imaging processing. To show that normalization of PT-PCL (nPT-PCL) against the maximum diameter of the tibial plateau may help to identify patients with patellar instability (PI). MR scans of 30 patients (13 females, age 32 ± 13 years) with known PI and 60 patients (31 females, age 39 ± 19 years) with no history of PI were reviewed. Two operators calculated TT-PCL, and PT-PCL nPT-PCL. Intraclass correlation coefficient, Student's t-test, Receiver Operator Characteristic curves, Spearman's Rho and McNemar's test were used. Interobserver reproducibility was 0.894 for PT-PCL for TT-PCL (95% CI = 0.839-0.930) and 0.866 for TT-PCL (95% CI = 0.796-0.912). The PT-PCL was 23.5 ± 3.8 mm in patients and 20.0 ± 2.7 mm in controls (P < 0.001). The TT-PCL was 22.9 ± 3.9 mm in patients and 20.5 ± 2.7 mm in controls (P = 0.002). Correlation between the PT-PCL and TT-PCL was R = 0.838, P < 0.001. The PT-PCL had 66.6% (95% CI = 0.542-0.790) diagnostic yield. The nPT-PCL was significantly higher in patients (0.302 ± 0.03) than controls (0.271 ± 0.03; P < 0.001) with 73.9% (95% CI = 0.628-0.851) diagnostic yield. The PT-PCL correlated with TT-PCL, with 66.6% diagnostic yield. The nPT-PCL may represent an additional index, with 73.9% diagnostic yield.