Disease severity affects knee range of motion but not strength deficits in knee osteoarthritis: a systematic review and meta-analysis

Objectives: To compare knee range of motion and muscle strength between individuals with symptomatic knee osteoarthritis and healthy controls, and to assess how Kellgren-Lawrence grade and measurement protocols affect these outcomes. Methods: A systematic search of PubMed, Scopus, and Web of Science identified studies comparing knee flexion/extension range of motion or flexor/extensor strength between patients with knee osteoarthritis and controls. Risk of bias was assessed with Joanna Briggs Institute tools. Pooled mean and standardized mean differences with 95% confidence intervals were calculated using random-effects meta-analyses. Results: Thirty studies were included. Compared with healthy controls, individuals with knee osteoarthritis showed significantly reduced knee flexion [MD = 16.30°, 95%CI (11.40, 21.21)] and extension [MD = 4.25°, 95%CI (2.30, 6.19)], with greater flexion loss in advanced KL grades. Knee osteoarthritis participants also demonstrated significantly lower strength across all contraction types: isometric [extensors: SMD = 0.86, 95%CI (0.57, 1.14); flexors: SMD = 0.52, 95%CI (0.30, 0.74)], concentric [extensors: SMD = 1.07, 95%CI (0.65, 1.50); flexors: SMD = 0.77, 95%CI (0.43, 1.12)], and eccentric extensor strength. Strength deficits were consistent across Kellgren-Lawrence grades, knee joint angles, and angular velocities during testing. Conclusions: Individuals with symptomatic knee osteoarthritis present with marked reductions in knee range of motion and strength. While range of motion impairments worsen with disease severity, strength deficits are stable across Kellgren-Lawrence grades and measurement protocols. Given the very low to low certainty of evidence, results should be interpreted with caution.