One hundred forty-seven patients with knee osteoarthritis (OA) were randomized to receive either a daily multistrain probiotic (Vivomix 112 billion) (n=72) or a placebo (n=75) for 12 weeks. The primary outcome was postural balance. Secondary outcomes included pain intensity (VAS), disease severity (WOMAC index), handgrip strength (HGS), gait speed, and plasma biomarkers of intestinal permeability (zonulin) and inflammation (CRP, 8-isoprostanes). A total of 136 patients completed the study (placebo: n=71, probiotics: n=65). Overall, probiotic supplementation significantly reduced pain intensity, disease severity, and inflammatory markers while improving balance, HGS, and walking speed (P<0.05 for all). However, no significant changes were observed in resting pain, knee flexion range of motion, or oxidative stress markers. These findings suggest that probiotic supplementation alleviates OA symptoms and enhances postural stability, possibly by reducing intestinal permeability and inflammation.