Medial meniscus tears in early-stage medial knee osteoarthritis: Prevalence and type in a Japanese cohort.

Background: Medial meniscus (MM) tears are closely associated with medial knee osteoarthritis (OA); however, their relationship in early-stage OA remains poorly understood. The purpose of this study was to elucidate the prevalence and types of MM tears in relation to age, gender, Kellgren-Lawrence (KL) grade, and MM extrusion among participants in the Kanagawa Knee Study, with the aim of potentially capturing the transition from healthy knees to early-stage medial knee OA.

Methods: The study analyzed 469 subjects (227 women, 242 men) aged 30-79 years. MM morphology was classified into six types using 3 T magnetic resonance imaging (3 T MRI): signal, horizontal tear, longitudinal tear, radial tear, complex tear, and root tear. The KL grades were automatically evaluated using KOALA software. The MM extrusion was measured on coronal MRI images.

Results: MM tears were present in 18.2 % of the subjects, with complex (7.9 %) and horizontal (7.7 %) tears being the most common. The prevalence of MM tears increased with age, with women in their sixties and seventies showing a significant increase compared to younger age groups. A marked gender difference was observed in patients in their sixties, with women showing a 45 % prevalence of MM tears compared to 19 % in men. The prevalence of MM tears increased with KL grade: 7 % in KL0, 14 % in KL1, 51 % in KL2, and 100 % in KL3-4. The prevalence was significantly higher in knees with MM extrusion ≥3 mm (90 %) than in those with MM extrusion <3 mm (11 %).

Conclusions: MM tears become more prevalent with advancing age, higher KL grade, and increased MM extrusion. The risk of MM tears appears to be considerably higher in women in their sixties than in men of the same age group.