"Between The Hammer and the Anvil": A Dynamic MRI Study of Meniscal Extrusion in Patients with Medial Meniscus Root-Tear

Background: Root-tear of the medial meniscus and accompanied meniscal extrusion can disrupt meniscal integrity; consequently leading to functional loss of the medial meniscus. The aim of our study is to assess medial meniscal extrusion in the presence of medial meniscus root-tear at increasing varus forces, imitating the adduction moment of the knee during gait.

Methods: We prospectively examined patients with medial meniscus root-tear and a control group of patients without a known knee pathology or knee complaints. Both groups underwent gait analysis testing on a force plate in order to calculate adduction moment. Coronal Proton density (PD) Magnetic resonance imaging (Siemens Magnetom Skyra 3 Tesla) was done at rest and with increasing varus forces according to the patient`s adduction moment. We then measured the extent of medial meniscal extrusion at increasing varus forces.

Results: We analyzed 19 patients (38 knees). There were 17 knees with medial meniscus root-tear in the index group and 21 knees in the control group. Average extrusion distance for the index group was 5.3mm without varus force, 6.4mm with 100% varus force and 6.8mm with 150% varus force. Average extrusion distance for the control group without varus force, 100% and 150% applied varus force was 1.7mm, 1.7mm and 1.9mm, respectively. Extrusion increase with 100% varus force was significantly higher in the index group (p=0.0002). The correlation between greater increase of meniscal extrusion with varus force and WOMAC pain, stiffness and function scores was ,r=0.14, r=0.26 and r=0.37 respectively.

Discussion:
Our study demonstrates an increase of meniscal extrusion during varus stress in patients with medial meniscus root-tear. This finding may help us better our understanding of the pathological movement of the torn and extruded medial meniscus during gait. Our results also suggests some correlation between meniscal extrusion and WOMAC scores, specifically with the WOMAC functional scale.