Extrusion of the anterior segment of the medial meniscus extrusion initiates knee osteoarthritis: evaluation using magnetic resonance imaging

Abstract Purpose Meniscus extrusion contributes to the progression of knee osteoarthritis (OA). It is not clear which site of the medial meniscus (MM) extrusion (MME) is greatest. Moreover, the relationship between sites of MME and progression of OA has not yet been elucidated. The purpose of this study was to determine which sites of MME that showed the greatest extrusion and to investigate the relationship between the presence of MM tears and MME, the relationship between the progression of OA and MME. Methods A cohort of 111 patients were studied retrospectively. The OA grade was classified using the Kellgren‐Lawrence (K‐L) grade. MME was measured at 13 positions from the anterior to the posterior segment using magnetic resonance imaging (MRI) with slices perpendicular to the MM (radial MRI). The relationship between the K‐L grade and the site of the MME was investigated. The patients were grouped as follows: The patients over 40‐years‐old were grouped as follows: patients with the K‐L grade ≤1 and without a MM tear (Group En (early, no meniscus tear)); patients with the K‐L grade ≤1 with a MM tear (Group Ep (early, positive meniscus tear)); patients with the K‐L grade ≥2 and without a MM tear (Group An (advanced, no meniscal tear)); patients over‐40 years‐old with the K‐L grade ≥2 and with a MM tear (Group Ap (advanced, positive meniscus tear)). And patients between 15 and 39‐years‐old with no abnormal findings on MRI were defined as control group (Group C). Results In the Groups En and Ep, MME was greatest in the anterior segment, and was greater in Group Ep than in Group En. In Groups Ap and Group C, extrusion was greatest in the middle segment. Conclusion The results suggest that MME predominantly occurred in the anterior segment with increasing age, after that, MM extruded at the middle segment with progression of OA and MM tear. Level of evidence IV