Soleus muscle weakness in Cerebral Palsy: muscle architecture revealed with Diffusion Tensor Imaging

Abstract

Cerebral palsy (CP) is associated with movement disorders and reduced muscle size. This latter phenomenon has been observed by computing muscle volumes from conventional MRI, with most studies reporting significantly reduced volumes in leg muscles. This indicates impaired muscle growth, but without knowing muscle fiber orientation, it is not clear whether muscle growth in CP is impaired in the along-fiber direction (indicating shortened muscles and limited range of motion) or the cross-fiber direction (indicating weak muscles and impaired strength). Using Diffusion Tensor Imaging (DTI) we can determine muscle fiber orientation and construct 3D muscle architectures to examine along-fiber length and cross-sectional area separately. Such an approach has not been undertaken in CP. Here, we use advanced DTI sequences with fast imaging times to capture fiber orientations in the soleus muscle of children with CP and age-matched, able-bodied controls. Physiological cross sectional areas (PCSA) were reduced (37 {+/-} 11%) in children with CP compared to controls, indicating impaired muscle strength. Along-fiber muscle lengths were not different between groups, but we observed large variance in length within CP group. This study is the first to demonstrate functional strength deficits using DTI and implicates impaired cross-sectional muscle growth in children with cerebral palsy.