Association between radial meniscal tears with and without posterior root involvement and subchondral insufficiency fracture of the knee on MRI: The mediating role of meniscal extrusion.

PURPOSE: The purpose of this study was to evaluate the relationship between subchondral insufficiency fracture (SIF) of the knee and radial meniscal tears on magnetic resonance imaging (MRI) and to examine within the medial compartment the potential mediating role of meniscal extrusion in this relationship. MATERIALS AND METHODS: A retrospective matched case-control study of knee MRI examinations 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 ratio [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 are strongly associated with SIF on MRI, particularly in the medial compartment. Meniscal extrusion explained a small proportion of this association, suggesting that additional biomechanical pathways are likely in play.