Reliability of maximum isometric arm, grip and pinch strength measurements in children (7-12 years) with unilateral spastic cerebral palsy

Purpose: To investigate test-retest and inter-rater reliability of maximum isometric arm muscle strength measurements using the hand-held dynamometer (HDD) and maximum isometric grip and pinch strength measurements using the Biometrics E-Link Evaluation System in children aged 7-12 years with unilateral spastic cerebral palsy. Materials and methods: All data were obtained using a test-retest study design. The study met the conditions of the COSMIN criteria to achieve good methodological quality. Results: For arm strength measurements, all test-retest reliability intraclass correlation coefficient (ICC) values and all but one inter-rater reliability ICC value indicated excellent reliability. For grip- and pinch strength measurements, all test-retest reliability and inter-rater reliability ICC values showed excellent reliability. The standard error of measurement values ranged from 4.97 to 11.36 N (HDD) and 0.37 to 1.81 kg (E-link). Smallest detectable change values ranged from 13.79 to 31.49 N (HDD) and 1.03 to 5.02 kg (E-link). Conclusions: The HDD and E-link system are usable measurement instruments for cross-sectional muscle strength measurements in children with unilateral spastic cerebral palsy. It is not clear if both instruments are usable to measure changes in muscle strength within an individual, especially if a child with unilateral spastic cerebral palsy has low muscle strength. Caution in the interpretation of changes in muscle strength is therefore necessary.