ABSTRACT
Spinal muscle cross-sectional area has been highly associated with spinal pathology. Despite the medium-high prevalence of spinal pathology in children, there is very limited knowledge regarding muscle size and growth pattern in individuals younger than 20 years of age. The aim of this study is to analyze the change in size and symmetry of spinal muscles (erector spinae, multifidus, psoas and quadratus lumborum) in children 2-20 years of age. We studied reformatted images from 91 abdominal computed tomographic scans of children aged 2-20 years, from an existing imaging dataset. The cross-sectional area of the muscles was bilaterally measured parallel to the upper endplate of the lumbar vertebrae L3-L5 and at true horizontal for S1. The cross-sectional area of the upper vertebral endplate was measured at spinal levels L3-L5. Results were analyzed according to six groups based on children's age: 2-4 years (group 1), 5-7 years (group 2), 8-10 years (group 3), 11-13 years (group 4), 14-16 years (group 5) and 17-20 years (group 6). Vertebral endplate and spinal muscles cross-sectional area increased with age. Two patterns were observed: Endplate, psoas and quadratus lumborum increased up to our 6th oldest age group (17-20), and multifidus and erector spinae reached their largest size in the 5th age group (14-16). The epaxial muscles (erector spinae and multifidus) reached their maximal cross-sectional area before skeletal maturity (18-21 years of age). The hypaxial muscles (psoas and quadratus lumborum) continued to increase in size at least until spinal maturity. Contributing factors for the differences in developmental pattern between the epaxial and hypaxial muscles might include functional, embryological and innervation factors. In conclusion, this research is the first to describe the cross-sectional area of spinal muscles in children. Future longitudinal studies are needed for further understanding of muscle development during childhood and adolescence. LEVEL OF EVIDENCE: level 2b, Retrospective cohort study.