Association between radial meniscal tears with and without posterior root involvement and subchondral insufficiency fracture of the knee: the mediating role of meniscal extrusion
Purpose The purpose of this study was to assess the association between knee subchondral insufficiency fracture (SIF) and radial meniscal tears and evaluated medial meniscal extrusion as a mediator. Materials and methods A retrospective matched case-control study of knee MRIs obtained from November 2021 to November 2024 was performed. MRIs were reviewed for SIF, meniscal tear morphology, and meniscal extrusion grade. Associations between radial tears and SIF (overall and medial compartment) were evaluated using conditional logistic regression adjusted for age, sex, and body mass index. Medial-compartment mediation was examined using a natural effects model with medial meniscal extrusion as the mediator. Results The cohort included 343 patients with SIF (65.4 ± 10.1 [standard deviation] years; 226 women) and 343 patients without SIF (66.4 ± 10.0 [standard deviation] years; 224 women). Compared with knees without radial tears, odds of SIF were higher in the presence of radial root tears (odds ration [OR], 7.62; 95% confidence interval [CI]: 4.40–13.21) and radial non-root tears (OR, 5.26; 95% CI: 2.48–11.15), with similar findings in the medial compartment. In mediation analysis, medial radial root tears showed an indirect association with medial SIF through medial meniscal extrusion (OR, 1.46; 95% CI: 1.16–1.84), accounting for 16.6% of the total effect. Conclusion Radial root and non-root tears were strongly associated with SIF, particularly in the medial compartment. Meniscal extrusion explained a small proportion of this association, suggesting that additional biomechanical pathways are likely in play.