Psychometric Evaluation of 2 New Upper Extremity Functional Strength Tests in Children with Cerebral Palsy

Abstract

Background: For children with unilateral spastic cerebral palsy (USCP), reduced muscle strength can lead to activity limitations. However, none of the existing measures of upper extremity strength measure strength in the context of functional activities in which strength must be maintained for several seconds. Objective: The objective of this study was to evaluate the psychometric properties of 2 newly developed functional hand and upper extremity muscle-strength tests (Cup-Task and Box-Task) in children aged 7 to 12 years with USCP. Design: A longitudinal study design was used. Methods: A standardized protocol with detailed descriptions of all procedures and measurements was used to determine test-retest reliability, interrater reliability, and criterion validity. Results: A total of 86 children (53 males, 33 females, mean age = 9.3 years) with USCP participated in this study, with a subset performing each measurement. Only the results of children who were able to perform the measurement were included for analysis. Excellent test-retest reliability (intraclass correlation coefficients = 0.887-0.944; 95% confidence intervals = 0.713-0.969) and interrater reliability (intraclass correlation coefficients = 0.896-0.960; 95% confidence intervals = 0.813-0.980) were observed. The Cup-Task Affected-Hand and Box-Task were moderately correlated with maximum isometric grip strength. The Cup-Task Nonaffected-Hand had a low correlation with maximum isometric grip strength. Limitations: Age, sex, and manual ability were not normally distributed, which could have influenced the results. Conclusions: For children with USCP who can perform the tasks, the Cup-Task and Box-Task are reliable and valid instruments for measuring functional upper extremity muscle strength.