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[The effect of the thoracic cage on the vertebral axial rotation of adolescent idiopathic scoliosis: a biomechanical study].

OBJECTIVE
To investigate the effect of the rib cage on the vertebral axial rotation of adolescent idiopathic scoliosis under axial load condition.


METHODS
Three dimensional finite element model of adolescent idiopathic scoliosis included and excluded thoracic cage was built based on the data of computer tomography. The model was imported into the preprocessor of the ANSYS 8.0 software for assigning boundary and loading conditions. Then the axial loading condition was simulated after entering the solution modular. The magnitude and direction of each vertebral axial rotation of the scoliotic spine were read and analyzed in the postprocessor of the ANSYS software.


RESULTS
The rib cage had a significant influence on the axial rotation of the vertebra above the structural curve and had no influence on the axial rotation of the lumbar and sacral vertebra. The effect of the thoracic cage on the axial rotation of the apical vertebra was limited. Under different loading conditions, the apical vertebra of both models rotated in the same direction. The magnitude of the vertebral rotation of both models has no statistical significance.


CONCLUSIONS
Adolescent idiopathic scoliosis can lead to the anatomical changes of the vertebra and the thoracic cage. The corresponding changes of biomechanical features of the scoliotic spine and rib cage would occur. The deformed thoracic cage could not maintain the rotation stability as the normal one.