Introduction: Free-hand thoracic pedicle screw placement is technically challenging and relies on a sound knowledge of the pertinent anatomic landmarks. Previously published placement techniques primarily focus on entry points and medial angulation. These techniques rely on tactile feedback during cannulation and are often subject to error. We propose a technique to facilitate safe and accurate placement of thoracic pedicle screws in a near-straight trajectory based on orthogonal cannulation relative the curvature of the spine.
Methods: We conducted a cadaveric and surgical evaluation of this orthogonal cannulation technique. For the cadaveric component of this study, twenty four pedicles (T1-12 bilaterally) were cannulated using the following technique: the entry point was marked 2 mm caudal to the TP-lateral facet junction for all levels. Medial angulation was determined by the level and preoperative imaging. The cephalad-caudal angulation was determined by advancing the probe orthogonal to the curvature of the spine at the corresponding level (Figure 1). An illustrative case is presented.
Results: All cannulations and screws were placed free-hand. After screw placement, lateral fluoroscopy at each level was utilized to determine the trajectory of the screw relative to the superior endplate. In all cases, there were no breaches after cannulation. Fluoroscopy images confirmed excellent trajectory for all screws. The screws were then removed, and again the pedicle tract was palpated to ensure there were no breeches. The Orthogonal Free Hand Technique was utilized in a patient requiring T8-L1 pedicle screw fixation. Eight thoracic pedicle screws were successfully placed without any breaches. Postoperative CT demonstrated excellent screw position.
Conclusions: The orthogonal free hand technique facilitates placement of thoracic pedicle screws, providing excellent near-straight trajectory at all levels.
Patient Care: Thoracic pedicle screws are routinely placed for thoracic instability. The free-hand technique has been used with increased frequency as it saves time and decreases radiation exposure as compared to other techniques. Anatomical landmarks are not often accurate. This new free-hand technique may provide more information for surgeons in order to safely place thoracic pedicle screws.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of thoracic pedicle screw placement, 2) Discuss, in small groups, the utility of orthogonal placement of pedicle scews, 3) Identify effectiveness of this technique in the placement of thoracic pedicle screws.
References: Holly LT, Foley KT: Three-dimensional fluoroscopy-guided percutaneous thoracolumbar pedicle screw placement. Technical note. Journal of neurosurgery 99:324-329, 2003
Kim YJ, Lenke LG: Thoracic pedicle screw placement: free-hand technique. Neurology India 53:512-519, 2005
Kim YJ, Lenke LG, Bridwell KH, Cho YS, Riew KD: Free hand pedicle screw placement in the thoracic spine: is it safe? Spine 29:333-342; discussion 342, 2004
Kim YW, Lenke LG, Kim YJ, Bridwell KH, Kim YB, Watanabe K: Free-hand pedicle screw placement during revision spinal surgery: analysis of 552 screws. Spine 33:1141-1148, 2008