Biomechanical Breakdown: The Roles of Radial Meniscal Tears and Bone Mineral Density in Subchondral Insufficiency Fractures of the Knee

Abstract

Paper 1: Association Between Radial Meniscal Tears With and Without Posterior Root Involvement and Subchondral Insufficiency Fracture of the Knee: The Mediating Role of Meniscal Extrusion Rationale and Objectives: The relative contributions of meniscal radial root versus non-root tears to knee subchondral insufficiency fracture (SIF) remain uncertain, as does the extent to which meniscal extrusion mediates this risk. We assessed the association between SIF and radial meniscal tears and explored the role of medial meniscal extrusion as a mediator. Materials and Methods: We performed a retrospective matched case-control study of knee MRIs obtained from November 2021 to November 2024. 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 cases (65.4 ± 10.1 years; 226 women) and 343 controls (66.4 ± 10.0 years; 224 women). Compared with knees without radial tears, odds of SIF were higher in the presence of radial root tears (OR, 7.62; 95% 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. Medial meniscal extrusion explained a small proportion of this association, suggesting that additional biomechanical pathways are likely in play. Paper 2: Association of Low Bone Mineral Density with Subchondral Insufficiency Fractures of the Knee in Women, and Exploring Effect Modification by Meniscal Root Tears Rationale and Objectives: To evaluate the association between low bone mineral density (BMD) and knee subchondral insufficiency fracture (SIF) in women, and to explore whether this association is modified by radial meniscal tears. Materials and Methods: In this case-control study, we included women with and without MRI-confirmed SIF who had available dual-energy X-ray absorptiometry T-score measurements. BMD was categorized using T-scores. We fit multivariable logistic regression models with BMD as the exposure and SIF as the outcome, adjusting for age and body mass index. We also conducted an exploratory stratified analysis to assess potential effect modification by radial root tears. Results: We analyzed 121 women with SIF (mean age, 69.1 ± 7.5 years) and 124 controls (70.4 ± 8.3 years). Median body mass index (Q1–Q3) was 27.2 (23.8–30.1) in cases and 27.4 (24.2–31.0) in controls. After adjustment, osteoporosis was associated with higher odds of SIF (OR 2.36; 95% CI, 1.06–5.24), whereas osteopenia (OR 1.37; 95% CI, 0.73–2.65) showed no significant association. In exploratory stratified analysis to test for effect modification, there was no significant interaction between low BMD and radial root tears (p-interaction = 0.146) , though small strata likely limited power to detect significant effect modification as evident by the overlapping wide 95% confidence intervals. Conclusion: Osteoporosis was associated with higher odds of SIF. Exploratory findings suggest possible effect modification by radial root tears.