Risk factors for meniscal body extrusion on MRI in subjects free of radiographic knee osteoarthritis: longitudinal data from the Osteoarthritis Initiative.

OBJECTIVE

To determine risk factors associated with increased meniscal body extrusion on knee magnetic resonance (MR) images in subjects free of radiographic osteoarthritis (OA).

METHODS

We selected 340 subjects (aged 45-55 years, mean [SD] body mass index 26.7 [4.4], 51% women) with Kellgren-Lawrence grade 0 in both knees and bilateral knee MR images available at the baseline, 24 months, 48 months, and 72 month exam from the Osteoarthritis Initiative (OAI). We assessed mid-coronal 3-T MR images from baseline through the 72-month exam. One observer measured widths of the tibia plateau and medial or lateral meniscal body extrusion for baseline and 72 months follow-up. Another observer assessed meniscal integrity at all four time points. We calculated an extrusion ratio ([meniscal body extrusion]/[tibia width] × 100) to account for knee size. We evaluated risk factors for increased meniscal body extrusion ratio from baseline to 72 months by a multivariable linear regression mixed model for medial and lateral compartment, respectively.

RESULTS

In the medial compartment female sex (β = 0.35; 95% confidence interval [CI] 0.16-0.53), incident meniscal tear (β = 0.29; 95% CI 0.22-0.55), and the baseline value of the extrusion ratio (β = 0.63; 95% CI 0.56-0.70) were associated with increased extrusion ratio by 72 months. Results were similar for the lateral compartment.

CONCLUSIONS

Only female sex, incident meniscal tear, and higher baseline value of extrusion are risk factors for increased meniscal body extrusion in subjects free of radiographic OA. The results suggest that meniscal extrusion may contribute to and mediate the well-known increase in knee OA incidence in middle-aged women.