Test-retest reliability of isokinetic dynamometry for the assessment of spasticity of the knee flexors and knee extensors in children with cerebral palsy

Objective: To assess test-retest reliability of the peak resistance torque and slope of work methods of spasticity measurement of the knee flexors and extensors in children with cerebral palsy (CP). Design: Test-retest reliability study. Setting: Pediatric orthopedic hospital. Participants: Fifteen children with CP. Intervention: Knee extensor and flexor spasticity was assessed with an isokinetic dynamometer using passive movements at 15 degrees, 90 degrees, and 180 degrees/s taken 1 hour apart. Main Outcome Measures: Peak resistive torque and work were calculated. The relative and absolute test-retest reliability was calculated by using intraclass correlation coefficients (ICCs) and Bland-Altman plots, respectively. Results: Relative reliability was good (ICC>.75) for slope-of-work and peak resistance torque measurements at a velocity of 180 degrees/s. whereas reliability of peak torque measurements was decreased (ICC<.51) at slower velocities for both muscle groups. The 95% limits of agreement of Bland-Altman plots contained most data points for both methods, but the width of the limits of agreement were wide. Conclusions: The measurement of spasticity of the knee extensors and flexors in children with CP using peak-resistance torque at 180 degrees/s and the slope of work method has acceptable relative test-retest reliability. However, the absolute reliability of spasticity data should be considered cautiously.