The purpose of this study was to assess the reliability of quadriceps muscle stiffness assessments in individuals with Osgood–Schlatter disease (OSD). Ten subjects were tested for four trials on two occasions within a 2-week period on a Kin-Com dynamometer. A regression coefficient was derived from force-angle data to determine stiffness. Intertriai and interday Intraclass correlations (ICC) and standard error of measurement (SEM) were derived from a repeated-measures ANOVA. Between-trial assessments were more reliable for the outer range 65 to 100° knee flexion (ICC = .95 & .81) than the inner range 35 to 65° knee flexion (ICC = .72 & .57) for both sessions. The average SEMs for outer and inner ranges (over 35°) were 1.1 and 1.3 N, respectively. Assessments between days were less reliable, which may reflect the weekly variation in the presentation of athletes' with- OSD. It remains unclear if the SEM lies within the limits of clinical significance.
The authors are with the Department of Functional Rehabilitation, School of Physiotherapy, Curtin University of Technology, Selby St., Shenton Park, Western Australia 6008.