In vivo axial rotation at the thoracolumbar junction: an investigation using low dose CT in healthy male volunteers.

Few studies report in vivo data on segmental spinal rotation due to complexities in resolving axial plane motion. Unilateral segmental rotation at the thoracolumbar junction in 18 healthy male volunteers was assessed using a low dose CT protocol. Subjects were positioned in end-range right trunk rotation and, following a digital scanogram, were scanned in the plane of the superior vertebral end-plates of T10-L3. The change in vertebral orientation between mobile segments, assumed to represent 'rotation', was calculated using standardized CT image references and vertebral landmarks. Greatest rotation appeared to occur with coronally oriented joints and the least change between segments where a mortice joint or the thoracolumbar transition was demonstrated. The mean trend was similar for individuals with either an abrupt or gradual change from coronal to sagittal plane orientation of their zygapophysial joints. Although not statistically significant, the gradual pattern demonstrated generally greater rotation at each segmental level compared to those subjects with an abrupt transition pattern. In contrast, routine supine thoracolumbar junction scans of patients showed lesser mean physiological rotation between all segments examined.