RESUMEN
OBJECTIVE: Although knee inflammation is thought to adversely affect joint function in patients with knee osteoarthritis (OA), the effects of reducing knee inflammation on gait biomechanics and strength are unknown. Our objectives were to compare ultrasound (US) measures of knee inflammation, gait biomechanics, knee extension and flexion strength, and pain before and after knee aspiration and glucocorticoid injection, and to explore associations among changes. METHODS: Forty-nine patients (69 knees) with symptomatic knee OA and synovitis were tested before and 3-4 weeks after US-guided knee aspiration and glucocorticoid injection. At each visit, participants completed US assessments for inflammatory features of knee OA, 3D gait analysis, isokinetic knee extension and flexion strength tests, and Knee Osteoarthritis Outcome Score (KOOS) pain subscales. Linear and polynomial mixed-effects regression models were used to investigate changes and their associations. RESULTS: Changes were observed for the synovitis score (unstandardized ß [post-injection minus pre-injection] -0.55/9 [95% confidence interval (95% CI) -0.97, -0.12]), effusion depth (-1.05 mm [95% CI -1.07, -0.39]), KOOS pain (unstandardized ß 5.91/100 [95% CI 1.86, 9.97]), peak external knee flexion and extension moments (KFM; 3.33 Nm [95% CI 0.45, 6.22]), KEM (-2.99 Nm [95% CI -5.93, -0.05]), and knee extension strength (4.70 Nm [95% CI 0.39, 9.00]) and flexion strength (3.91 Nm [95% CI 1.50, 6.81]). The external KFM increased during 13-38% and 76-89% of stance post-injection. When controlled for time, greater synovitis was associated with lower knee extension strength, while lower pain was associated with increased knee extension and flexion strength. CONCLUSION: In patients with knee OA and synovitis, reduced inflammation and pain after aspiration and glucocorticoid injection are associated with changes in knee gait biomechanics and strength.