Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment.

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.