Tomodensitometry measurements for in vivo quantification of mechanical properties of scoliotic vertebrae

Objectives. This in vivo study investigated the mechanical properties of sc oliotic vertebrae especially in the apical zone. Design. A method based on computed tomography images and finite element mes hing had been developed to quantify and visualise the bone density distribu tion of scoliotic vertebrae. Background Most of scoliotic studies performed considered only geometrical parameters. Method. Computed tomography examination had been performed on 11 girls pres enting idiopathic scoliosis, Using in-house image processing software and t he pre-post processor Patran, a finite element mesh of each vertebral body and a mapping of each cancellous bone slice were proposed allowing the bone density distribution to be visualised. The mechanical properties were deri ved from predictive relationships between Young's modulus and computed tomo graphy number. Geometrical (unit mass) and mechanical centres were calculat ed and compared in order to quantify the role of mechanical property distri bution on the apex zone of the scoliotic spine. Results. In the coronal plane, compared to the geometrical centre, the mech anical centre was shifted forward in the concavity (0.54 mm) of the curvatu re except for two vertebrae. In the sagittal plane. the mechanical centre w as shifted forward in the back (0.26 mm) except for three vertebrae. The sh ift forward by slice was made in a same way for each slice (0.63 mm), excep t at the end plates (0.58 mm), Discussion. The result values obtained were small but significant because t he curvatures were low and the vertebrae were not wedged. Besides, one can observe that the scoliotic deformation evolution seemed to modify the mecha nical property distribution.