O61: Are medial gastrocnemius and tibialis anterior morphology indicative of kinematic and kinetic impairment during gait in children with spastic cerebral palsy and a control group of typically developing peers?

Abstract

1. Introduction Children with spastic cerebral palsy (SCP) present with impaired muscle growth compared to typical development (TD), where the deficits in muscle volume lead to lower force-generation, and reduced functional capacity. With respect to gait, moderate associations in the stance phase were found between plantar flexor work and muscle volume in unilaterally impaired SCP adolescents [1], whilst similar findings were reported between the sagittal plane ankle angle at initial contact and pennation angle of the tibialis anterior [2]. Neither investigation compared these findings to data of a control cohort. It is also unknown to what extent the proliferation of non-contractile tissue within SCP muscles [3] influences muscle function. 2. Research Question To what extent can muscle volume and echo-intensity of the medial gastrocnemius and tibialis anterior explain ankle impairments in the stance phase of gait? 3. Methods Two cohorts were recruited for this investigation (TD n=12; SCP n=33). The cohort of SCP children was naive to previous orthopaedic and/or neurological surgery, or BTX-A injections six months prior to measurement. Using 3D freehand ultrasound (combination of an ultrasound and motion-tracking system [4]), 3D reconstructions of the medial gastrocnemius (MG) and tibialis anterior (TA) were created. Muscle volume and echo-intensity (EI) were extracted using OsiriX (www.osirix-viewer.com). EI was calculated as the mean for the entire muscle, whilst muscle volume was also expressed relative to body-mass. A Vicon system and AMTI force-plates collected kinematics and kinetics of the ankle at a self-selected walking speed. The mean of three good trials for peak ankle power generation during the stance phase, and the sagittal plane ankle angle at initial contact were extracted. Ankle power was also normalized to body-mass. T-tests were used to compare the differences between cohorts, whilst the Pearson correlation coefficient was used to evaluate correlations between variables. Significance was set to p