Change of vertebral orientation, between the supine position and the prone position

Our aim was to assess the change of vertebral orientation, expressed in the sagittal plane, in the transversal plane and in the frontal plane, at each level from T1 to S1 between the supine position (like in in a CT scan) and the prone position lying on bolsters like in an OR.

Thirty-six patients were selected and included for a total number of one hundred and forty-eight vertebral levels. There were 30 females and 6 males. The mean age was 15 years and 9 months. A semi-automatic image processing technique and software (3D slicer), with a custom-made python script add-on, was used for each patient: paired preoperative CT scan and intraoperative cone beam computed tomography (CBCT) scan were processed to acquire complete spinal reconstructions in a consistent 3D coordinate system. The aim was to automatically compute a set of sagittal, transversal, and frontal rotations of each vertebral level of the same patient describing the 3D vertebral rotation between the supine position and the prone position lying on bolsters.

For sagittal analysis, the results showed a behavior in the evolution of rotation depending on the level. Between T01 and T10, the rotation was between - 14° and - 8°. Between T10 and L05, the sagittal rotation increased from - 10° up to + 10°. For frontal and transversal analysis, the rotations were under 6.5°.

These results could be valuable to perform a safe virtual templating: the information given by the virtual templating seems to be more accurate in the transversal plane than in the sagittal plane.