An extrapedicular approach to the placement of screws in the thoracic spine: an anatomic and radiographic assessment

Abstract

Study design: A radiographic and anatomic study of an extrapedicular method of screw placement in cadaveric thoracic spines.

Objective: To evaluate an alternative method of thoracic vertebral body screw fixation using an extrapedicular screw technique. To evaluate the anatomic safe zones and proper starting point for this alternative approach to the placement of screw fixation in the thoracic spine.

Summary of background data: Despite the clinical successes reported with thoracic pedicle screw-rod constructs, controversy exists about the safety of this technique in pedicles that are anatomically too small for transpedicular fixation. An alternative method of extrapedicular screw fixation was evaluated in this present study.

Materials and methods: Two fresh, unfixed, adult cadavers were obtained randomly; 6.0-mm AO Synthes pedicle screws were placed using an extrapedicular approach bilaterally from T3 to T10. The screws were placed according to one defined method described later. Computerized tomographic (CT) images were obtained. The position of each screw was analyzed. The cadavers were then dissected with the screw pathway exposed and the relation of the screw to surrounding anatomy documented.

Results: All screws did not penetrate the spinal canal. All screws were within the pedicle rib unit and did not penetrate the neural foramen or pleura.

Conclusion: This study, although only introductory, indicates the potential for extrapedicular vertebral body fixation in the thoracic spine. Biomechanical evaluations are presently being conducted to evaluate the use of extrapedicular thoracic screw fixation.