The posterior cruciate ligament-posterior femoral cortex angle (PCL-PCA): A Precise Indicator of Knee Decompensation in Skeletally Immature ACL-Injured Patients

PURPOSE: This study aimed to determine the most reliable and precise method for measuring the buckling phenomenon of the posterior cruciate ligament (PCL) in skeletally immature patients on magnetic resonance imaging (MRI). The posterior cruciate ligament (PCL)-line sign, PCL angle (PCLA), PCL inclination angle (PCLIA) and PCL-posterior cortex angle (PCL-PCA) were considered. Secondary aims were to (1) compare PCL buckling between healthy and ACL-injured patients to establish a discrimination threshold, (2) assess its validity against other MRI parameters. The hypothesis was that the PCL-PCA is the most reliable and precise method to detect knee decompensation.

METHODS: Fifty-five ACL-injured patients with open physes were matched with 51 controls by gender and skeletal age. The PCL buckling phenomenon was measured on MRI using four methods, each repeated after two weeks. The presence of a lateral collateral ligament (LCL) sign, medial/lateral anterior tibial translation (ATT) and meniscal bone angle (MBA) were considered. Intra- and inter-observer reliability were assessed using Cohen's Kappa and intra-class correlation coefficients (ICCs). Standard error of measurement (SEM) and minimal detectable change (MDC) were calculated. Group comparisons used t-tests and chi-square tests; receiver-operating characteristic curves identified optimal thresholds, and Pearson correlations assessed relationships between PCL measures and knee decompensation indicators.

RESULTS: PCL-line, PCLA and PCL-PCA showed excellent intra- and inter-observer reliability (ICCs > 0.90), while PCLIA was rated good (ICC = 0.75-0.90). PCL-PCA showed the highest precision (SEM = 2.0°) and best discrimination between healthy and ACL-injured patients (sensitivity: 80%, specificity 74.1%, cut-off ≤ 31.5°) It correlated with medial/lateral MBA (0.36; p < 0.001, 0.37; p < 0.001, respectively) and ATT (-0.59; p < 0.001, -0.52; p < 0.001, respectively), yet did not differ between positive and negative LCL signs (n.s.).

CONCLUSION: PCL-PCA showed the highest reliability/precision to measure the PCL buckling phenomenon. Its correlation with other indicators of knee decompensation confirms that PCL-PCA can be used to detect knee decompensation in children.

LEVEL OF EVIDENCE: Level III.