Structures at risk from pedicle screws in the proximal thoracic spine: computed tomography evaluation.

BACKGROUND CONTEXT

Pedicle screw placement in the proximal thoracic spine may result in unwanted bicortical breach. An understanding of the potential structures at risk is paramount to safe screw placement.

PURPOSE

To assess the anatomic location of structures at risk with the placement of bicortical pedicle screw fixation in the proximal thoracic spine.

STUDY DESIGN

Retrospective radiographic review.

PATIENT SAMPLE

Twenty patients with dedicated computed tomography (CT) scans of the thoracic spine.

OUTCOME MEASURES

Radiographic parameters on CT.

METHODS AND MATERIALS

Computed tomography was performed on 20 patients and analyzed from T1 to T4 for proximity of major structures at risk with breach of the anterior vertebral body cortex from pedicle screw placement. Descriptive statistics, analyses of variance and post hoc paired t tests were used to analyze screw position relative to the esophagus, trachea, aortic arch, carotid, and vertebral arteries.

RESULTS

One hundred sixty potential anterior cortical violation positions were analyzed. Left-sided pedicle screws posed a significantly higher risk (p<.05) to the esophagus at T1-T3; in particular, the left T2 screw was significantly closer (p<.05). Right-sided pedicle screws posed a significantly higher risk to the trachea at T2-T4 (p<.05). The right T3 and T4 screws posed the greatest risk to the trachea and right main bronchus, respectively (p<.05). The carotid and vertebral arteries were not at risk for injury. The aortic arch was present at T4 in 70% of patients and was not at risk.

CONCLUSIONS

Careful preoperative evaluation with CT is warranted to determine anatomic structures at risk when placing proximal thoracic pedicle screws. Left-sided screws pose the greatest risk to the esophagus; right-sided screws pose the greatest risk to the trachea. The carotid and vertebral arteries, along with the aortic arch are at minimal risk for injury.