Reproducibility of concentric isokinetic and isometric strength measurements at the hip in patients with hip osteoarthritis: A preliminary study

To determine the reproducibility of isokinetic and isometric hip flexion, extension, abduction and adduction strength scores in patients with hip osteoarthritis (N = 16) and healthy subjects, testing was conducted twice 7 days apart. The patient group (PG) consisted of 16 subjects with unilateral or bilateral osteoarthritis of the hip (11 women, 5 men; age 56-75y). The control group (CG) included 13 age-matched healthy subjects (9 women, 4 men; age 54-73y). The standard error of measurement (SEM) served as the reproducibility outcome parameter. The highest SEM values were obtained for hip extension measurements (15.4-16.7 Nm), followed by hip adduction (7.9-11.8 Nm) and hip flexion measurements (5.2-7.5 Nm). The smallest values were quantified for hip abduction measurements (4.7-7.7 Nm). PG showed larger values in all isometric measures except for hip extension and isokinetic hip abduction. When the 95% confidence interval is incorporated, these SEMs become significant. Thus clinicians should be aware of the large measurement error in patients with hip OA. Adequate preparations and firm fixation of the pelvis are key elements to achieve reproducible results.