The effect of hypokyphosis on the biomechanical behavior of the adolescent thoracic spine

Deformity in adolescent thoracic spine has high prevalence worldwide. The objective of this work was to study the biomechanical behavior on the thoracic spines of adolescents under asymmetric ligament load in kyphosis and rectified kyphosis. Two finite element models of an adolescent thoracic segment, T5-T10, were generated with every bone component, intervertebral discs, the flavum, intertransverse and supraspinous ligaments. The three-dimensional geometry of the T5-T10 was generated with Autodesk (R) Maya (R), and HyperMesh (R) version 14.0 was used to generate the finite element models. Asymmetric ligament load of 10 N was applied in the T8-T9, with and without axial load of 400 N in the T5 vertebra. Rectified kyphosis showed the highest rotational displacement of the T8-T9 unit: 0.16 degrees with axial load and asymmetric ligament load, and 0.22 degrees with asymmetric ligament load alone. Kyphosis exhibited rotational displacement of 0.11 degrees and 0.12 degrees, respectively, for the same load conditions. Rectified kyphosis subjected to an asymmetric ligament force showed greater inoperability of the facet joints, and therefore greater vulnerability to vertebral rotation. The results suggest the need for greater attention to the vertebral assessments in the sagittal plane, beginning from the growth spurt period, to adopt preventive therapeutic in vertebral deformities such as adolescent idiopathic scoliosis.