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.