Introduction: Knee osteoarthritis is a leading cause of disability and medical costs. The effect of whole-body vibration in knee osteoarthritis is controversial. The aim of this study was to assess the effects and safety of whole-body vibration on pain, stiffness, physical function, and muscle strength in patients with knee osteoarthritis.

Methods: PubMed, Scopus, Web of Science, Physiotherapy Evidence Database (PEDro) and EMBASE databases were searched (date last accessed 1 April 2021) using the key words "vibration" and "knee osteoarthritis", to identify all randomized controlled trials related to whole-body vibration and knee osteoarthritis. Outcomes related to pain, stiffness, physical function, muscle strength, adverse events were included. The risk of bias and quality were assessed by the Cochrane Collaboration tool and PEDro scale. A systematic review and meta-analysis were performed. Subgroup analysis was performed for low- and high-frequency interventions.

Results: A total of 14 randomized controlled trials involving 559 patients with knee osteoarthritis met the inclusion criteria. Nine studies were good-quality trials (PEDro score=6-8), and 5 studies were fairquality trials (PEDro score=4-5). Ten studies were included in the meta-analysis. One study showed negative effects of whole-body vibration on knee osteoarthritis. The duration of whole-body vibration ranged from 4 to 24 weeks. Meta-analysis revealed that whole-body vibration with strengthening exercises has a significant treatment effect on pain score (standardized mean difference (SMD) = 0.46 points, 95% confidence interval (95% CI) = 0.20-0.71, p = 0.0004), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC-function) (SMD = 0.51 points, 95% CI = 0.27-0.75, p < 0.0001), Timed Up and Go (TUG) test (SMD = 0.82 points, 95% CI = 0.46-1.18, p < 0.00001), extensor isokinetic peak torque (SMD = 0.65 points, 95% CI = 0.00-1.29, p = 0.05), peak power (SMD = 0.68 points, 95% CI = 0.26-1.10, p = 0.001), and extensor isometric strength (SMD = 0.44 points, 95% CI = 0.13-0.75, p = 0.006). Both low-frequency (10-30 Hz) and highfrequency (30-40 Hz) whole-body vibration were associated with significant changes in pain, physical function, and knee extensor strength (p < 0.05). WBV was not associated with significant changes in stiffness, balance ability, quality of life, and knee flexor strength. No adverse events were reported.

Conclusion: Meta-analysis showed that low-frequency and high-frequency whole-body vibration had additional positive effects compared with strengthening exercises alone on pain, knee extensor muscle strength, and physical function in individuals with knee OA. Whole-body vibration with strengthening exercises can be incorporated into treatment protocols.