Association between changes in muscle strength and pain in persons with meniscal tear and osteoarthritis

OBJECTIVE: Strengthening-based physical therapy (PT) is frequently recommended for persons with knee osteoarthritis (OA) and meniscal tear. On average, knee OA patients experience pain improvement while undergoing PT, but whether these changes are accompanied by changes in muscle strength remains an important research question. DESIGN: We used data from subjects randomized to PT in the Meniscal Tear in Osteoarthritis Research (MeTeOR) trial. Key elements, measured at baseline and 3 months, included quadriceps and hamstrings strength (in pounds) and Knee Injury and Osteoarthritis Outcome Score (KOOS) Pain subscale (0–100; 100 worst). We examined the linear association between change in strength and change in pain over 3 months. RESULTS: 111 subjects (mean age 57.1, average baseline hamstrings strength 27.5 (SD 14.7), average baseline KOOS 48.0 (SD 17.0)) experienced an average increase in hamstring strength of 3.5 lbs (SD 9.4) and an average decrease in KOOS Pain of 17.1 points (SD 17.4). The correlation between change in hamstrings strength and change in KOOS Pain was weak (Pearson r = 0.17; 95% CI-0.016–0.345). A multivariable linear regression model adjusting for baseline pain showed that a 10-pound increase in hamstrings strength was associated with a 2.9-point (95% CI−0.05−5.9) reduction in KOOS Pain. The association between changes in quadriceps strength and pain was even weaker than that for hamstrings pain. CONCLUSION: We observed small increases in strength and weak associations between strengthening and pain relief, suggesting that pain relief achieved during PT likely arises from multiple factors beyond strengthening alone.