Reproducibility of hand-held ankle dynamometry to measure altered ankle moment-angle characteristics in children with spastic cerebral palsy

Abstract Background In children with spastic cerebral palsy, the range of motion of the ankle joint is often limited. Measurement of range of motion may be hampered by a non-rigid foot deformity. We constructed a hand-held instrument which allows measurements of static ankle angle and moment in children with cerebral palsy while correcting for foot deformity. This study aimed to test the reproducibility of the instrument and to use it for measuring ankle moment-angle characteristics in individual children who are typically developing and children with cerebral palsy. Methods Ankle angles and moments were measured at five standardized positions in ten children who are typically developing and ten children with cerebral palsy. The intraclass correlation coefficient was calculated for test–retest reliability. For precision, the standard error of measurement and smallest detectable difference were determined. The ankle range of motion and the slope of the moment-angle curve were determined, both towards plantar flexion and dorsiflexion. Findings The reproducibility study revealed a high reliability of the dynamometer at 5 repetitions (> 0.97). Precision lies within 5° for angle measurements and within 0.2 Nm for moment measurements. In the children with cerebral palsy, the range of motion towards dorsiflexion was 18° lower and the slope of the moment-angle curve towards dorsiflexion was substantially higher. Interpretation We developed a hand-held dynamometer which allows reliable and precise measurements of static ankle angle and moment in children with cerebral palsy. The hand-held dynamometer allows corrections of foot deformities and is qualified to reproducibly evaluate moment-angle characteristics in a clinical context.