Dose‐Response Effects of Tai Chi and Physical Therapy Exercise Interventions in Symptomatic Knee Osteoarthritis

Abstract Background Therapeutic exercise is a currently recommended nonpharmacological treatment for knee osteoarthritis (KOA). The optimal treatment dose (frequency or duration) has not been determined. Objective To examine dose‐response relationships, minimal effective dose, and baseline factors associated with the timing of response from 2 exercise interventions in KOA. Design Secondary analysis of a single‐blind, randomized trial comparing 12‐week Tai Chi and physical therapy exercise programs (Trial Registry # NCT01258985 ). Setting Urban tertiary care academic hospital Participants A total of 182 participants with symptomatic KOA (mean age 61 years; BMI 32 kg/m 2 , 70% female; 55% white). Methods We defined dose as cumulative attendance‐weeks of intervention, and treatment response as ≥20% and ≥50% improvement in pain and function. Using log‐rank tests, we compared time‐to‐response between interventions, and used Cox regression to examine baseline factors associated with timing of response, including physical and psychosocial health, physical performance, outcome expectations, self‐efficacy, and biomechanical factors. Main Outcome Measures Weekly Western Ontario and McMasters Osteoarthritis Index (WOMAC) pain (0‐500) and function (0‐1700) scores. Results Both interventions had an approximately linear dose‐response effect resulting in a 9‐ to 11‐point reduction in WOMAC pain and a 32‐ to 41‐point improvement in function per attendance‐week. There was no significant difference in overall time‐to‐response for pain and function between treatment groups. Median time‐to‐response for ≥20% improvement in pain and function was 2 attendance‐weeks and for ≥50% improvement was 4‐5 attendance‐weeks. On multivariable models, outcome expectations were independently associated with incident function response (hazard ratio = 1.47, 95% confidence interval 1.004‐2.14). Conclusions Both interventions have approximately linear dose‐dependent effects on pain and function; their minimum effective doses range from 2‐5 weeks; and patient perceived benefits of exercise influence the timing of response in KOA. These results may help clinicians to optimize patient‐centered exercise treatments and better manage patient expectations. Level of Evidence II