Investigation of extrusion of the medial meniscus under full weight-loading conditions using upright weight-loading magnetic resonance imaging and ultrasonography.

BACKGROUND: Meniscal morphology under full weight-loading conditions is currently unknown. This study aimed to evaluate extrusion in the medial meniscus between unloaded and upright-loaded conditions in healthy adults using upright magnetic resonance imaging (MRI) and ultrasonography and to investigate the relationship between MRI and ultrasonography in upright-loaded conditions. METHODS: Eighteen healthy adult volunteers (13 men and 5 women) participated in the study. MRI and ultrasonography were performed with patients in the supine, double-leg upright (DLU), and single-leg upright (SLU) positions. Medial, anterior, and posterior extrusions of the medial meniscus against the tibial edge were evaluated and compared across the three positions. Medial extrusion correlations between MRI and ultrasonography were examined. Demographic data and hip-knee-ankle (HKA) angles were measured and correlated with changes in the medial extrusion. The medial meniscal extrusions detected via MRI and ultrasonography were compared across the three positions. Correlations were examined using Pearson's correlation coefficients. RESULTS: Negative correlations were found between the change in medial extrusion of the medial meniscus and HKA angle (MRI: r = -0.52, ultrasonography: r = -0.51). Although no significant differences among the three conditions were observed for the anterior and posterior extrusions of the medial meniscus, the medial extrusion of the medial meniscus was significantly greater in DLU and SLU positions than that in the supine position for MRI and ultrasonography (P < 0.05). Positive correlations for the medial extrusion of the medial meniscus were found between MRI and ultrasonography in all three positions (supine: r = 0.74, DLU; r = 0.71, SLU; r = 0.61). CONCLUSIONS: Although no significant differences in anterior and posterior extrusions of the medial meniscus were seen across the studied positions, the medial meniscus was found to undergo significant medial extrusion during upright weight-loading conditions. The strong correlation between MRI and ultrasonography highlighted the usefulness of ultrasonography. LEVEL OF EVIDENCE: Level IV.