Synovial Fluid Characteristics and Pain Recovery Trajectory Following Rehabilitation in Patients with Meniscal Tears: A Retrospective Cohort Study

Background: Meniscal tears are a common cause of knee pain and functional limitation, yet determinants of pain recovery following rehabilitation remain incompletely understood. Structural imaging findings often show limited correlation with clinical symptoms. This study aimed to evaluate longitudinal pain trajectories after rehabilitation in patients with meniscal tears and to investigate whether synovial fluid characteristics and structural joint degeneration are associated with pain improvement. Methods: This retrospective cohort study included 59 patients with meniscal tears who underwent structured rehabilitation. Structural degeneration was assessed using the Whole-Organ Magnetic Resonance Imaging Score (WORMS). Synovial fluid cytology evaluated neutrophil predominance (PNL) and erythrocyte positivity. Pain intensity was measured using the Visual Analog Scale (VAS) at 3 months, 6 months, and 1 year. Longitudinal changes were analyzed using the Friedman test, and predictors of pain improvement (ΔVAS from 3 months to 1 year) were evaluated using multivariable linear regression. Results: VAS scores decreased significantly over time (p < 0.001), indicating sustained pain reduction during follow-up. In the multivariable regression model (F(4, 54) = 2.80, p = 0.035), 17% of the variance in pain improvement was explained (R2 = 0.17). Synovial erythrocyte positivity was modestly associated with greater longitudinal pain reduction (β = 0.75, 95% CI 0.15–1.36, p = 0.016). Age was also a significant predictor (β = 0.025, p = 0.043), whereas WORMS score and PNL positivity were not significantly associated with pain improvement. Conclusions: Pain recovery following rehabilitation in patients with meniscal tears appears to be influenced more by intra-articular biological characteristics than by structural imaging severity alone. Synovial erythrocyte positivity may indicate a potentially reversible inflammatory phenotype associated with higher early pain but greater subsequent improvement. These findings support a multidimensional model of knee pain and suggest that synovial characteristics may help improve clinical risk stratification during rehabilitation planning.