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

Objectives. This in vivo study investigated the mechanical properties of scoliotic vertebrae especially in the apical zone. Design. A method based on computed tomography images and finite element meshing had been developed to quantify and visualise the bone density distribution of scoliotic vertebrae. Background. Most of scoliotic studies performed considered only geometrical parameters. Method. Computed tomography examination had been performed on 11 girls presenting idiopathic scoliosis. Using in-house image processing software and the 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 derived from predictive relationships between Youngʹs modulus and computed tomography number. Geometrical (unit mass) and mechanical centres were calculated and compared in order to quantify the role of mechanical property distribution on the apex zone of the scoliotic spine. Results. In the coronal plane, compared to the geometrical centre, the mechanical centre was shifted forward in the concavity (0.54 mm) of the curvature except for two vertebrae. In the sagittal plane, the mechanical centre was shifted forward in the back (0.26 mm) except for three vertebrae. The shift forward by slice was made in a same way for each slice (0.63 mm), except at the end plates (0.58 mm). Discussion. The result values obtained were small but significant because the curvatures were low and the vertebrae were not wedged. Besides, one can observe that the scoliotic deformation evolution seemed to modify the mechanical property distribution.