Aims and Objectives: Extrusion of the medial meniscus in MRI is an indirect radiological sign for a meniscus root tear. However, a recent study has shown that ultrasound-detectable dynamic extrusion is considered physiological in healthy volunteers. The aim of our study was to analyze the dynamic meniscal extrusion in patients with proven root injury in ultrasound. Our hypothesis was that dynamic extrusion is reduced in patients with root injury of the medial meniscus compared to healthy volunteers. Materials and Methods: Inclusion criteria for this prospective study were MRI signs for a root lesion of the medial meniscus (ghost sign, extrusion > 3 mm). An age matched group of healthy volunteers served as control. Exclusion criterion was osteoarthritis > II° of the medial compartment according to Kellgren & Lawrence. The extrusion of the medial meniscus (MME) of the affected knee was measured by ultrasound (US) in supine position and under full weight bearing. Results: 25 patients with a medial root lesion were included in the study. The evaluation of the ultrasound results revealed a significant decreased dynamic medial displacement of the meniscus in patients with root injury. In the supine position, the mean medial meniscus extrusion was 3.60 mm (± 1.00 mm). In the standing position, the mean medial meniscus extrusion increased to 3.72 mm (± 0.96 mm). The mean delta-extrusion was 0.11 mm (± 0.17 mm). This difference was statistically not significant. In 14 patients, no dynamic extrusion was detectable at all. All patients belonging to the medial root tear group had a significant varus deformity (mechanical axis hits the tibial joint line more than 15 mm medially form the center). In the control group, the mean medial meniscus extrusion was 1.34 mm (± 0.37 mm) in supine position and 2.20 mm (± 0.34 mm) under full weight bearing. The mean delta-extrusion was 0.85 mm (± 0.30 mm). The difference in mean delta-extrusion between the root tear and control group was statistically significant. Conclusion: Ultrasonography is a diagnostic tool to detect the dynamic extrusion of the medial meniscus. Lack of dynamic extrusion (“dead meniscus sign”) may serve as an indicator for medial root injury.
No dynamic extrusion in medial meniscus root lesions - an ultrasound study
