Roentgenographic evaluation of vertebral rotation.

To examine the accuracy of vertebral rotation determinations made from roentgenographic pedicle-shadow offset measurements, roentgenograms were made of fifteen cadaver vertebrae with different sagittal and frontal inclinations and longitudinal axis rotations ranging from 15 degrees left to 45 degrees right. It was found that significant uncertainties arise when vertebral rotation is evaluated from measurements of pedicle-shadow offset: true and apparent offsets in a single vertebra differ markedly; vertebrae from different spines have different offsets for the same degree of rotation and the same inclinations; and changes in the sagittal and frontal inclinations of a single vertebra alter its offset in the same manner as changes in rotation. From these results, it seems unlikely that precise measurements of rotation changes in spines with mild or moderate scolioses, for example, can be made from anteroposterior roentgenograms.