Statistical Shape and Fibre Orientation Model for Muscle Architecture Characterisation of the Medial Gastrocnemius

Cerebral palsy (CP) is a heterogeneous, neurodevelopmental disorder arising from a static brain lesion and leading to progressive muscle degeneration. Quantitative understanding of 3D muscle morphology and fibre architecture effects of CP are lacking. Here, we present a novel imaging and computational method to investigate morphology and 3D fibre orientations of skeletal muscles in adolescents with CP.

Principal component analysis was performed on data derived from conventional MRI and diffusion tensor MRI; principal components (PCs) described dominant variations in each cohort. We applied this method to the medial gastrocnemius muscles of seven young people with CP and eight typically developing controls to quantitatively assess deviations in muscle structure associated with CP.

Morphology and architecture models in each cohort had similar variance of dominant features, with size being the predominant mode of variation in both cohorts. The first three PCs accounted for a cumulative variance of CP and TD cohort of 96 and 97%, and 95 and 97% for shape models and shape and fibre orientation models, respectively. Size differences were greatest in the proximal and distal regions, rather than middle, of the muscle. Models revealed localised variation in 3D fibre orientations between the two cohorts in medial-distal region of the muscle. Local variations were observed in the medial- distal regions of the mean muscle of about 10° in the TD model compared to the CP model. PCs of architecture models indicated that greater localised angular differences in the 3D fibre orientations were associated with larger-than-average muscles.

This work offers insights into both muscle morphology and architecture of the medial gastrocnemius in individuals with CP, including variations of overall size and localised muscle fibre orientations. The quantitative descriptions of muscle architecture we present here may contribute to greater understanding of muscle function and dysfunction and may motivate imaging-informed perspectives on therapeutic interventions for CP.