Factors associated with longitudinal change of meniscal extrusion in overweight women without clinical signs of knee osteoarthritis

Abstract

Purpose: Previously, we showed a significant and largely independent association between meniscal extrusion and incident knee osteoarthritis (KOA). With the present study, we aimed to identify variables associated with longitudinal change in meniscal extrusion, which might be used as possible targets for prevention of developing KOA. Methods: We used data from the PROOF trial, a preventive RCT which evaluated a high-risk population of 407 middle-aged overweight women (BMI ≥ 27 kg/m2). Meniscal extrusion was assessed on the mid-coronal slice of an MRI which were performed at baseline and after 30 months follow-up. Outcomes were the absolute change in meniscal extrusion (mm) or the absolute change in relative extrusion (%), evaluated for the medial as well as the lateral meniscus. Relative extrusion was calculated by dividing the meniscal extrusion by the width of the meniscus. Based upon literature, several factors were hypothesized to be associated with longitudinal change in meniscal extrusion, including baseline age, BMI, postmenopausal status, malalignment, quadriceps strength, physical activity, meniscal tears, having a past of knee injury and the presence of Heberden’s nodes and change in BMI over 30 months. Linear GEE models were used to model the effect of these covariates on the absolute change in extrusion. Separate models were used for the change in lateral and medial extrusion. An unstructured covariate matrix was used. Furthermore, models were made for the change in relative meniscal extrusion following the same procedure. Lastly, all these models were adjusted for tibial width, to take the difference in knee size into account. Results: For 343 subjects, sufficient MRI data were available for analysis. A 5 kg/m2increase in BMI resulted in an increase of medial extrusion of 0.16 mm (95% CI: 0.05, 0.26). The other factors included in the model were not significantly associated with a change in medial extrusion after 30 months. The model for lateral meniscal extrusion showed that an increase in BMI of 1 kg/m2in 30 months was associated with an increase of lateral meniscal extrusion of 0.07 mm (95% CI: 0.04, 0.11). None of the other factors included in the model influenced the change in lateral extrusion after 30 months. Adjusting for tibial width did not influence the results. The model for change in relative medial meniscal width only resulted in a significant increase of relative meniscal extrusion after 30 months of 2.9% (95 % CI: 1.15, 4.65) per 5 kg/m2. No other significant changes in relative medial extrusion were found. Relative lateral extrusion was increased by 0.57% (95% CI: 0.26, 0.88) with an increase in BMI of 1 kg/m2in 30 months. Adjusting for tibial width did not result in a change of significance. Conclusions: Baseline BMI and change of BMI over time were associated with change in meniscal extrusion of the medial and lateral meniscus, respectively. BMI therefore might be used as a target for reducing extrusion and by that decelerate the development of KOA. None of the other assessed variables showed significant results, which is quite remarkable given the findings of previous studies.