The geno-biomechanical similarity between functional and idiopathic scoliosis from kinematic, muscle activation, vertebral loading and the pathological gene expression perspectives

Adolescent functional scoliosis arises from complex interactions among inappropriate habits, incorrect force field induced by asymmetric muscle activation and potentially abnormal gene expression during development. Growing evidence suggests that untreated functional scoliosis may progress to idiopathic scoliosis, while debatable in the latest SOSORT guidelines for American adolescents. To characterize the biomechanical mechanisms underlying this potential progression, we integrated multi-modal data, including kinematics, muscle activation, vertebral loading and gene expression to comprehensively understand how subjects with functional scoliosis presents similarity with patients with idiopathic scoliosis compared with healthy controls. The results from 33 subjects with functional scoliosis, 27 subjects with idiopathic scoliosis and 18 healthy controls show that subsets of subjects with functional scoliosis present a closer kinetics, muscle activation pattern to those with idiopathic scoliosis compared with healthy controls, according to the comprehensively assessed features from inertial measure unit (IMU) and surface myoelectric (sEMG) signals. Subject-specific musculoskeletal modelling also shows a closer pattern in bone loading between functional and idiopathic scoliosis compared with healthy controls. The genetic expression analysis further indicates a significant correlation between the phenotype of functional scoliosis with the highest pathological information and the pathological genetic mutation for idiopathic scoliosis. Our results provide insights into the complex interaction across kinetic, biomechanical and genetic aspects of functional and idiopathic scoliosis, suggesting that a subset of functional scoliosis may represent early manifestations of idiopathic scoliosis. These insights may inform future updates to guidelines for the management of functional scoliosis.