The influence of spasticity on goniometric range of motion measurement in children with cerebral palsy

Spasticity may introduce bias in passive range of motion (ROM) measurements in children with cerebral palsy. This study aimed to explore the impact of spasticity on the reliability and potential measurement bias of goniometric assessments of ankle dorsiflexion and knee extension in children with unilateral spastic cerebral palsy (USCP). Thirty-two children aged 6–17 years with unilateral spastic cerebral palsy were included. Two blinded investigators measured ROM on the spastic and contralateral sides using a two-axis goniometer, and spasticity was graded with the Modified Ashworth Scale. The primary outcome was the between-side difference in inter-examiner measurement bias, analysed using paired t-tests and confidence intervals. Secondary outcomes—agreement and reliability—were assessed using Bland–Altman plots and intraclass correlation coefficients (ICC). No clinically meaningful differences in ROM measurement bias were found between the spastic and contralateral sides for ankle dorsiflexion (extended knee: mean difference − 0.22°, 95% CI: − 2.53 to 2.09; flexed knee: 0.78°, 95% CI: − 3.57 to 2.01), knee extension (0.31°, 95% CI: − 1.63 to 1.01), or hamstrings angle (0.50°, 95% CI: − 2.53 to 3.53). ICC indicated high inter-rater reliability. These findings support the use of goniometry as a reliable tool for assessing joint mobility in clinical and research settings. Results were reliable for measurements on a spastic and contralateral limb and no clinically significant bias was found.