Leg-arm length ratios correlate with severity of apical vertebral rotation in girls after school screening for adolescent idiopathic scoliosis (AIS): a dynamic pathomechanism in the initiation of the deformity?

There is increasing support for the view that the unique human bipedalism and the erect posture are prerequisites for the pathogenesis of adolescent idiopathic scoliosis (AIS). How human bipedalism may contribute to the pathogenesis of AIS is not clear. In normal humans, axial rotations and counter-rotations of the trunk are carried out frequently and forcibly in activities that are not performed by quadrupeds. Some workers have analysed gait in AIS subjects, others have studied torsions in lower limb bones, but there are only two reports on leg-arm ratios in relation to AIS. In this paper, leg-arm ratios studied in relation to the spinal deformity in scoliosis screening referrals, reveal a highly significant correlation with the apical vertebral rotation but not the Cobb angle of the scoliosis curves. We suggest that leg-arm proportions and movements during gait involving pelvi-spinal axial rotations and thoracic counter-rotations contribute a dynamic pathomechanism to early AIS from whatever cause and involving the thoracic cage. Curve progression needs other mechanisms that may include a central nervous system failure to control structural asymmetry of vertebral axial rotation, and biomechanical spinal growth modulation.