Steeper medial posterior tibial slope is associated with medial meniscal extrusion and early‐onset knee osteoarthritis in middle‐aged Japanese women: A longitudinal cohort study

Abstract Purpose This study primarily aimed to evaluate the longitudinal association between proximal tibial morphologic parameters and medial meniscal extrusion for 5 years and examine the relationship of both proximal tibial morphologic parameters and medial meniscal extrusion with the onset of knee osteoarthritis (OA) in middle‐aged Japanese women. The secondary aim was to identify factors associated with changes in medial meniscal extrusion. Methods A longitudinal retrospective cohort of middle‐aged Japanese women without radiographic OA at baseline was followed for 5 years. No radiographic OA was defined as a Kellgren–Lawrence grade of 0 or 1 on plain radiographs. Proximal tibial morphologic parameters, including the medial and lateral posterior tibial slope (PTS) and medial proximal tibial angle (MPTA), were assessed using magnetic resonance imaging. OA onset was defined as progression to Kellgren–Lawrence grade ≥2 on follow‐up plain radiographs. Medial meniscal extrusion was measured using ultrasonography at baseline and at 5 years, and the change in medial meniscal extrusion was calculated. Linear regression analyses were performed to identify independent predictors and optimal thresholds for OA onset. A p value < 0.05 was considered statistically significant. Results In total, 134 women (mean age 54.1 ± 8.9 years; mean body mass index 21.6 ± 2.8 kg/m 2 ) were included. A steeper medial PTS (mPTS) was associated with greater change in medial meniscal extrusion ( p < 0.01), whereas MPTA ( p = 0.73) and lateral PTS ( p = 0.20) were not associated with changes in medial meniscus extrusion. The mPTS and change in medial meniscal extrusion were independent predictors of OA onset (both p < 0.01). Conclusions Steeper mPTS and greater change in medial meniscal extrusion may be critical structural risk factors for the early development of knee OA in middle‐aged Japanese women. Incorporating assessments of mPTS and change in medial meniscal extrusion into clinical protocols may aid in the early initiation of preventive interventions for knee OA. Level of Evidence Level IV.