Association between baseline meniscal extrusion and long-term incident knee osteoarthritis in two different cohorts

Objective: Previously, we identified a significant association between meniscal extrusion and short-term incident knee osteoarthritis (KOA). To validate these findings, we evaluated long-term incident KOA in knees with meniscus extrusion, using two different cohorts. Methods: We used data from the PROOF study, which evaluated a high-risk population of overweight women, and a female subcohort of the population-based Rotterdam Study (RS). Meniscal extrusion was defined as ≥ 3 mm on MRI. Outcomes were incident radiographic (KL ≥ 2) or clinical KOA according to the ACR criteria, assessed at 6.6 years (PROOF) and 5.1 years (RS). With generalized estimating equations, we determined the association of knees with and without baseline meniscal extrusion and incident KOA, adjusting for confounders. Furthermore, we computed the population attributable risk percentage (PAR%) of meniscal extrusion. Results: PROOF: of 421 available knees 23% had baseline meniscal extrusion. Incident radiographic KOA was significantly higher in knees with meniscal extrusion compared to those without (adjusted OR 2.54, 95% CI 1.34, 4.80; p = 0.004; PAR 21%). Incident clinical KOA was also significantly higher (adjusted OR 2.44, 95% CI 1.29, 4.60; p = 0.006; PAR 19%). RS: 46% of 872 available knees had meniscal extrusion. Incident radiographic KOA was significantly higher (adjusted OR 9.86, 95% CI 2.13, 45.67; p = 0.002; PAR 77%). Incident clinical KOA was borderline significantly higher (adjusted OR 2.65, 95% CI 0.96, 7.30; p = 0.06; PAR 44%). Conclusion: Meniscal extrusion is significantly associated with long-term incident KOA. A high number of incident cases were attributable to extrusion.