Association between Varus Mechanical Alignment and Medial Meniscus Tears: A Retrospective Study

Varus mechanical alignment of the knee is a recognized contributor to medial compartment osteoarthritis (OA). Medial meniscus tears (MMT) frequently occur with knee OA. The present study aimed to analyze the association between mechanical alignment and MMT. We retrospectively analyzed 201 knee joints from patients with knee pain who underwent whole-leg weight-bearing radiographs and magnetic resonance imaging (MRI). Mechanical alignment was quantified using the hip-knee-ankle angle (HKAA), measured independently by two radiologists with excellent interrater reliability (intraclass correlation coefficient = 0.93). MMTs were assessed on MRI with high diagnostic agreement (κ = 0.87). Based on MRI findings, participants were classified into two groups: those with MMT (<i>n</i> = 104) and those without MMT (<i>n</i> = 97). Group comparisons were performed using <i>t</i>-tests and chi-square tests. Patients with MMT had greater varus alignment (HKAA: -6.2 ± 3.4 vs. -2.4 ± 1.4 degrees, <i>p</i> < 0.001), were older (53.7 ± 8.3 vs. 49.3 ± 9.0 years, <i>p</i> < 0.001), and had higher body mass index (26.6 ± 3.0 vs. 25.2 ± 2.4 kg/m², <i>p</i> = 0.001). Sex distribution did not differ between groups (<i>p</i> = 0.479). Logistic regression identified HKAA as the only independent predictor of MMT. When entered as a continuous variable, each additional degree of varus increased the odds of MMT nearly 2-fold (adjusted OR = 2.01, 95% confidence interval [CI]: 1.64-2.47, <i>p</i> < 0.001). The complementary binary analysis showed that patients with varus alignment had over a 3-fold higher risk of MMT compared with those with neutral or valgus alignment (OR = 3.25, 95% CI: 1.85-5.72, <i>p</i> < 0.001). Posterior horn tears were the most common subtype (47.1%), followed by multisite tears (33.7%). MMTs are strongly associated with varus mechanical alignment. Each incremental degree of varus increased the likelihood of MMT, and posterior horn tears were the most prevalent subtype. These findings highlight the pivotal role of mechanical alignment in the prevention, early detection, and management of MMT.