Children with cerebral palsy with reduced selective control show stereotyped muscle synergies across activities

• Published in: Gait & posture Vol. 106; pp. S289 - S290
• Main Authors: Febrer-Nafría, Míriam, Carey, Hannah, Willaert, Jente, Van Den Bosch, Bram, Desloovere, Kaat, Van Campenhout, Anja, De Groote, Friedl
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2023
• ISSN: 0966-6362; 1879-2219
• DOI: 10.1016/j.gaitpost.2023.07.073

Physics-based computer simulations that predict the effect of treatments on gait in children with cerebral palsy (CP) have the potential to improve the clinical decision-making. To this end, it is important to accurately model patient-specific non-selective motor control. Muscle synergies can be used to describe the ability to selectively control muscles. Children with CP present fewer synergies [1], which are more variable between subjects [2], than typically developing individuals. We want to investigate if muscle synergy weights reflect patient-specific impaired selective muscle control. We hypothesise that the number of synergies and the percentage of shared synergies are related to selective scores, and that children with reduced selective control show more stereotyped synergies across activities. We collected data from 6 children with spastic CP, GMFCS score I or II. Selective control assessment of the lower extremity was performed by the SCALE [3] (Fig. 1a). We collected EMG of eight muscles per leg during walking and three functional movements: squat, sit to stand, and counter movement jump. We assessed the number of synergies that were needed for each activity to explain 90% of the variance accounted for [2]. Moreover, we identified the number and percentage of shared synergies between walking and each functional movement, and across all four activities. A pair of synergies were considered shared if Pearson’s correlation coefficient was higher than 0.7067 (which corresponds to the critical value of r² for 8 muscles and p=0.05) [4], and if they were shared between gait and each functional movement, then the synergy was considered shared across activities. We found that the number of synergies, both for walking and each of the functional movements, was lower for lower selective scores (Fig. 1b). We did not find a clear relation between the percentage of shared synergies and selective scores (Fig. 1b). Indeed, some subjects with the same score shared synergies while others did not. Actually, the shared synergies for subjects with reduced selectivity showed greater consistency; i.e., the standard deviation per each muscle weight was lower than for subjects with higher selectivity (Fig. 1c). Fig. 1: (a) SCALE total scores (10 means no impairment) per subject and leg. (b) Number of synergies and percentage of shared synergies per groups of SCALE score. (c) Example of shared synergies across all activities for some of the children. [Display omitted] Although we did not find a direct relation between the SCALE and the percentage of shared synergies between gait and each of the functional movements, shared synergies across activities were in general more consistent for subjects with lower SCALE scores. In future work, we aim to describe individual motor control deficits in patients with CP by means of muscle synergies, to include motor control deficits in our current simulation workflow [5].