Why do children with unilateral cerebral palsy struggle with the single leg stance test? A kinematic and centre of pressure analysis.

Background: Children with unilateral cerebral palsy often report difficulty with balance in everyday life. The single leg stance test is a challenging task, requiring rapid sensory input and precise motor adjustment. The purpose of this study was to examine how children with cerebral palsy perform this test, compared to typically developing children.

Methods: Three-dimensional kinematics of the trunk and lower limbs of 10 children with cerebral palsy and 15 children with typical development were captured as they performed a single leg stance test on their non-dominant leg on a force platform. Stance time, joint kinematics and centre of pressure sway were measured and examined.

Findings: There was evidence of shorter single leg stance performance and increased mediolateral centre of pressure sway in children with cerebral palsy. Coronal plane movement at the subtalar joint and foot was reduced (-6.0° (-10.9, -1.2°)), while proximally there was greater trunk movement in the coronal (13.5° (2.4°, 24.5°)) and transverse planes (9.9° (0.7, 19°)) and pelvis movement in the transverse plane (6.1° (1.7, 10.5°). An association existed between stance time and mediolateral centre of pressure sway (p < 0.01), with an average reduction in stance time of 0.15 s for every 1 mm/s increase in mediolateral sway.

Interpretation: Children with cerebral palsy showed poor mediolateral control of centre of pressure sway, leading to shorter stance time. They have a less effective coronal foot-tilt strategy and excessive trunk and pelvis movement. Interventions aimed at improving single leg stance performance should consider addressing both ankle / foot and trunk motor control.