In Vivo Assessment of Weight-Bearing Knee Flexion Reveals Compartment-Specific Alterations in Meniscal Slope

PurposeThe purpose of this study was to determine the effects of flexion angle on meniscal slope during partial weight-bearing knee flexion.MethodsForty-eight sagittal sequences were performed on 12 patients (6 male patients, 6 female patients; 25.7 ± 10.5 years) during partial weight bearing in an open magnetic resonance imaging (MRI) scanner at full extension, 60°, 90°, and maximum knee flexion. A previously published method was used to measure the meniscal slope for each compartment using manual digitalization. A general linear model was used to test for effects of compartment and flexion angle on meniscal slope.ResultsThe mean maximum flexion angle achieved was 125° ± 10.5°. A significant main effect of compartment (P < .01) and flexion angle (P < .01) on meniscal slope was observed. A significant interaction between compartment and angle was also detected (P < .01). Specifically, the lateral meniscal slope was significantly more horizontal than the medial meniscus slope at full extension (P = .017) but significantly more posterior at all other angles. In addition, the lateral meniscus displayed a greater change in posterior slope across the range of motion compared with the medial meniscus. Significant correlations were found in medial meniscal slope at full extension and at maximum knee flexion (P = .031).ConclusionsThe results showed that meniscal slope in healthy knees increased significantly with knee flexion for both menisci, with significantly greater changes in the lateral meniscus. Furthermore, a lack of correlation was observed between the meniscal slope in extension and the meniscal slope at increasing flexion angles, questioning the efficacy of measuring the meniscal slope only in extension as commonly described. Overall, this study has provided valuable insight into how meniscal slope changes with knee motion.Level of EvidenceLevel IV, therapeutic case series.