Defining anatomical landmarks for simulated juxtapedicular screw placement for posterior spinal fusion in adolescent patients with scoliosis.

PURPOSE

To define anatomical landmarks on the vertebrae at each spinal level for surgeons to use intraoperatively as a guide for the placement of juxtapedicular screws in the setting of hypoplastic or absent pedicles.

METHODS

Preoperative computed tomography (CT) of patients with adolescent idiopathic scoliosis (AIS) was analyzed for thoracic pedicles ≤ 3 mm wide, measured between the outer cortices at the isthmus, as these may require a juxtapedicular screw for safe placement. For these pedicles, a simulated juxtapedicular screw was placed into the vertebrae using image reconstruction software. The distance from the screw's insertion point was measured in the axial plane to the medial and lateral borders of the superior articular process (SAP) and to the posterior tip of the transverse process (TP), and in the sagittal plane to the junction of the SAP and TP. Screw trajectory angle was measured between the longitudinal axis of the screw and the sagittal and axial planes.

RESULTS

Of 6324 pedicles, a total of 378 pedicles (6.0%) met inclusion. The average distance to the medial and lateral borders of the SAP was 14.7 ± 3.4 mm and 10.7 ± 5.4 mm, respectively; to the tip of the TP was 9.0 ± 3.9 mm, and to the TP/SAP junction 2.8 ± 1.6 mm. The average angle in the axial plane was 21.1 ± 4.4° and in the sagittal plane it was - 4.2 ± 3.6°.

CONCLUSIONS

Preoperative CT scans were used to map a safe starting point and trajectory for juxtapedicular screw placement in thoracic vertebrae. These findings can assist surgeons with thoracic pedicle screw placement.