Muscle and bone growth in the lower legs of typically developing children and ambulant children with cerebral palsy: a mixed longitudinal study

Background Longitudinal data on skeletal muscle growth in children are scarce, so little is known about developmental trajectories of skeletal muscle size, the relative timing of muscle and skeletal growth and how cerebral palsy (CP) affects growth. Methods We conducted a mixed longitudinal study of 252 children aged 5–18 years, including 66 children with CP. MRI-based measurements of lower leg muscle volumes and tibia lengths were obtained on 2–3 occasions over ~3 years and used to estimate age- and sex-specific reference curves for growth velocities. Results At the population level, peak adolescent growth velocity in lower leg muscle volume was higher and occurred later in typically developing boys (155 cm 3 /yr at 14.2 years) than in girls (117 cm 3 /yr at 12.1 years). In children with CP, median muscle growth and tibia length velocities were ~41% and 11% smaller, respectively, than in age- and sex-matched typically developing children. Muscle growth velocities in children with CP were low at all ages and did not systematically vary by degree of functional impairment, topography of CP or treatment history. Conclusion This study establishes reference data for muscle and bone growth velocities during typical childhood development which can be used for child- and muscle-specific assessments of growth impairments. Impact Mixed longitudinal MRI data were used to construct reference curves for growth velocities of lower leg muscle volumes and tibia lengths in typically developing children aged 5–18 years. At the population level, peak adolescent muscle growth velocity was about one-third greater and occurred 2 years later in boys than in girls. Peak muscle growth velocities occurred 2 years after peak tibia length velocities, showing the asynchronous development of muscle and bone. Children with cerebral palsy exhibit larger deficits in growth velocities of muscles (~41% smaller than in age- and sex-matched typically developing children) than in tibia length (~11%).