The relationship between strength and function in females with juvenile rheumatoid arthritis.

OBJECTIVE: To describe the relationship between isokinetic concentric and eccentric quadriceps strength and function in females with juvenile rheumatoid arthritis (JRA). METHODS: Twenty girls with JRA aged 6 to 16 years participated in the study. Function and strength were measured on one occasion. Isokinetic concentric and eccentric quadriceps torque was measured on the Kin-Com dynamometer. Function was measured with the Childhood Health Assessment Questionnaire (CHAQ) and the Canada Fitness Award 50 m run. Pain and joint count were taken as measures of disease activity. Pain was assessed on a visual analog scale through parent- and self-report. Correlations between function, standardized torque values, pain, and joint count were determined. Stepwise multiple regression analyses with function as the predicted variable were performed. RESULTS: Correlations between standardized torque and CHAQ scores were moderate (r = -0.48, p = 0.03 for concentric torque and r = -0.43, p = 0.06 for eccentric). Correlations between torque and run scores were also moderate (r = -0.48, p = 0.03 for concentric, r = -0.31, p = 0.19 for eccentric). Pain and total joint count were the best predictors of CHAQ score (r2 = 0.80), while concentric torque was the best predictor of running ability (r2 = 0.23). CONCLUSION: Quadriceps torque was moderately correlated to function in girls with JRA. Function as determined on the CHAQ was best predicted from measures of disease activity, while function as determined on the 50 m run was best predicted from concentric quadriceps torque. Further research is required to determine a cause-effect relationship between strength and function in girls with JRA.