The apical vertebrae in mild scoliotic spines are subject to extremum weight moments

The aetiopathogenesis for AIS is multifactorial and undetermined. The weight of the upper body segments on the spine can generate lateral bending moments which can potentially exacerbate the deformity during growth. Literature shows that the lateral bending moment is maximum at the apical vertebra of Lenke1 scoliosis patients which was expected. We utilized a recently developed thoracolumbar musculoskeletal model in AnyBody modeling system to simulate 13 patient-specific mild AIS cases. In most cases, the results of the model confirm the literature. However, we found that the weight moment on the apex of the AIS deformity was minimum in some of the cases, which happened due to the C7 lateral deviation towards the major curve apex. This finding indicates that the C7 moves in the same direction as the major curve apex in a compensatory reaction, and this can end up as a vicious cycle.