Non-uniform 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 fibre 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 fibres, with passive stress also being lower in AL fibres at longer sarcomere lengths (3.0 – 3.4 µm). AL samples had significantly lower actin and nebulin content compared to GR, while myosin and titin did not differ significantly. Fibre cross-sectional area (CSA) was significantly smaller in AL than GR, whereas collagen, fat content, and 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.