Nonuniform hip adductor muscle deficits in children with cerebral palsy: a comparison between the gracilis and adductor longus.

Cerebral palsy (CP) is the most common cause of childhood physical disability and often results in muscle weakness, spasticity, and contractures. Although cellular and sarcomeric impairments have been documented in muscles from children with CP, systematic comparisons of multiple muscles within the same child remain limited. Therefore, we investigated within-subject differences in single muscle fiber mechanics, sarcomeric protein content, and histological properties between patient-paired adductor longus (AL) and gracilis (GR) muscle biopsies obtained from eleven children with severe spastic CP. Maximal active stress and active elastic modulus were significantly lower in AL than GR for both type I and type II muscle fibers, with passive stress also being lower in AL fibers at longer sarcomere lengths (3.0-3.4 µm). AL samples had significantly lower actin and nebulin content compared with GR, whereas myosin and titin did not differ significantly. Fiber cross-sectional area (CSA) was significantly smaller in AL than GR, whereas collagen, fat content, and myosin heavy chain (MHC) isoform distribution did not differ between the two muscles. These findings suggest that muscles with overlapping function can undergo substantially different cellular adaptations within the same child with CP, and treating the hip adductors as a single functional unit may obscure notable muscle-specific adaptations.NEW & NOTEWORTHY To our knowledge, this is the first study to show that two hip adductor muscles from the same children with spastic cerebral palsy differ in single muscle fiber force production and thin-filament protein content. These findings suggest that cellular muscle properties in cerebral palsy can vary substantially between muscles within the same child, even among muscles commonly treated as one functional group.