Isometric strength measurements in children with arthritis: Reliability and relation to function

OBJECTIVE: To examine the reliability of testing strength in children with juvenile arthritis (JA), and to determine the relationship between strength and function. METHODS: Children with JA were tested for grip and pinch strength (n = 32). Isometric force produced by hip abductors and knee extensors was tested with a hand-held dynamometer (n = 29). Two therapists both performed each of the tests twice so that intrarater and interrater reliability could be examined. Function was measured by means of the Childhood Health Assessment Questionnaire (CHAQ) and performance on a 50-meter run. Reliability was examined with intraclass correlations (ICC). The relationships of strength and function were determined with Pearson and Spearman correlations. RESULTS: All measures demonstrated good intrarater (ICC = 0.92-0.97) and interrater (ICC = 0.80-0.95) reliability. Grip strength and pinch were correlated with the CHAQ (r = -0.45 and -0.33, respectively), while hip abduction and knee extension torque were correlated with rankings on the 50-meter run (rho = -0.34 and -0.38, respectively). CONCLUSION: Isometric strength can be reliably measured in children with arthritis in a clinical setting.