We used computerized tomographic scans and subsequent dissections to
evaluate the position of ninety pedicle screws that had been inserted
bilaterally into the fourth through twelfth thoracic vertebrae of five
fresh-frozen cadavera. The screws had been inserted by five experienced
spine surgeons without the use of radiographs or imaging studies. Of the
ninety screws, thirty-seven were found to have penetrated the cortex of the
pedicle. Twenty-one screws had penetrated the medial cortex and entered the
spinal canal, and sixteen had penetrated the lateral cortex. The aorta and
the esophagus were at greatest risk for injury after advancement of the
screws beyond the anterior vertebral cortex. Computerized tomographic scans
of the thoracic spine in nineteen living controls who did not have a spinal
abnormality confirmed the proximity of the posterior mediastinal structures
to the misplaced screws.