Medial Meniscal Extrusion Evaluation With Weight‐Bearing Ultrasound: Correlation With MR Imaging Findings and Reported Symptoms

OBJECTIVES: To compare medial meniscal extrusion on weight‐bearing ultrasound (US) with supine US and magnetic resonance (MR) imaging correlating with meniscal pathology and reported symptoms. METHODS: IRB approved study with informed consent. Patients obtaining routine knee MR imaging for suspected knee pathology were prospectively evaluated with supine and weight‐bearing US of the medial meniscus. Meniscal extrusion was measured independently by two fellowship‐trained musculoskeletal radiologists. Correlation was made to presence or absence of meniscal degeneration or tear on MR imaging, as well as reported symptoms. Statistical significance was calculated via intraclass correlation coefficient (ICC) and analysis of variance (ANOVA). RESULTS: Ninety‐nine knees from 95 subjects (50 males, 45 females; mean age 45 ± 15 years) were included. Mean medial meniscal extrusion measured at US for a normal meniscus (n = 36) was 0.8 mm when supine, increasing to 1.6 mm on weight‐bearing. Mean meniscal extrusion in subjects with mucoid degeneration (n = 20) and those with meniscal tears (n = 43) was 1.6 mm, increasing to 2.3 mm with weight bearing. Inter‐reader reliability showed ICC values of 0.853 to 0.940. There was a significant difference in medial meniscal extrusion comparing subjects with a normal medial meniscus at magnetic resonance imaging (MRI) and subjects with either meniscal degeneration or tear. There was no significant difference in degree of meniscal extrusion between subjects with meniscal degeneration or tear. There was trend of worsening symptoms and increasing functional limitations moving from normal meniscus to meniscal degeneration to meniscal tear. CONCLUSIONS: A normal meniscus shows lesser mobility between supine and upright position, than a pathologic meniscus. Both mucoid degeneration and meniscal tear demonstrate extrusion in the supine position, which increases with weight‐bearing position.