Introduction: Percutaneous pedicle screw placement is being used more frequently in minimally invasive spine surgery. One method is to cannulate, tap, and place a pedicle screw over a guide wire (e.g., Kirschner wire) along the proposed screw trajectory under biplanar fluoroscopy. As the guide wire is advanced through the pedicle, however, there is risk of penetrating the anterior wall of the vertebral body and injuring structures ventral to the spinal column. This study identifies vascular structures that are at risk when performing this procedure.
Methods: Fifteen spines were analyzed by drawing standard pedicle screw trajectories on computed tomography (CT) axial images from T1 to S1. These trajectories were extended 1.0 cm, and 2.5 cm beyond the ventral border of the vertebral body. Vascular structures in the path of these trajectories were identified.
Results: Several consistent relationships were noted between vascular structures and pedicle screw trajectories. Between T10 and L4, the aorta was within 1 cm and 2.5 cm of the left pedicle screw trajectory in 80% (84/105) and 69% (31/45) instances, respectively. Between T9 and L5, the inferior vena cava (IVC) was within 1.0 cm and 2.5 cm of the right pedicle screw trajectory in 35% (37/105) and 19% (20/105), respectively. Between T4 and T8, the azygos vein was within 1.0 cm of the right pedicle screw trajectory in 31% (23/75) instances.
Conclusions: This study demonstrated consistent relationships between pedicle screw trajectories and the aorta, IVC, and azygos vein that place these structures at risk. Consideration must be given in the placement of K-wires during minimally invasive percutaneous pedicle screw placement to avoid damaging critical vascular structures.
Patient Care: Understand structures at risk with placement of percutaneous pedicle screw placement.
Learning Objectives: 1. Identify structures at risk with percutaneous placement of K-wire for pedicle screw instrumentation.
2. Understand advantages to knowing anatomic structures anterior to the vertebral body at various spine levels.
3. Discuss vascular structures most at risk with percutaneous procedures.