We studied the morphology of the thoracic vertebrae in the spines of
seventeen human cadavera in order to define parameters that could be used
as guidelines for the placement of hooks and screws in the pedicles to
obtain internal fixation. We also reviewed computerized tomographic scans
of nineteen thoracic spines in living patients who had no evidence of any
vertebral deformity. The transverse diameter of the pedicle, which helps to
determine the size of the screw, ranged from a mean (and standard
deviation) of 4.5 +/- 1.2 millimeters in the fourth thoracic vertebra to a
mean of 7.8 +/- 2.0 millimeters in the twelfth thoracic vertebra. The
pedicles were inclined anteromedially throughout the thoracic spine, and
the angle ranged from 0.3 degree toward the midline in the twelfth thoracic
vertebra to 13.9 degrees in the fourth thoracic vertebra. The morphometric
data revealed wide variations in the dimensions of the pedicles,
demonstrating the importance of accurate preoperative imaging with
transaxial computerized tomographic scans to visualize the precise osseous
margins and angles of insertion of the thoracic pedicles.