Accuracy of Freehand Versus Modified Funnel Technique for Pedicle Screw Insertion in the Thoracic Spine

To describe a new pedicle screw insertion technique, a modification of the funnel technique, and to compare this technique with conventional freehand screw insertion regarding their accuracy and complications in the thoracic spine.

Three hundred forty-three patients who underwent a posterior spinal fusion with different etiologies were retrospectively analyzed. In 84 patients, pedicle screws were placed using the freehand technique, and in 259 patients, the modified funnel technique was used. Screw malposition was evaluated in the immediate and final follow-up in anteroposterior and lateral spinal radiographs by two independent observers. The rates of incorrect pedicle screws and complications, surgical duration, and estimated blood loss were compared between the groups.

A total of 6141 pedicle screws (1468 in the freehand group, 4673 in the modified funnel group) were evaluated. The rate of incorrect pedicle screws was higher in the freehand group (12.0% vs. 4.6%, p=0.001). The surgical time was shorter in the modified funnel group (190.9 ± 57.0 vs. 174.1 ± 47.6 min; p=0.017). The estimated blood loss was similar between the groups (1391.50 ± 570.01 vs. 1264.13 ± 602.29 mL; p=0.053). There were 82 intraoperative pedicle fractures but no neurologic complications in either group.

The modified funnel technique provides more accurate pedicle screw insertion in the thoracic spine in the presence of dysplastic pedicles in conjunction with axial rotation compared with the freehand technique. Furthermore, surgical time may be reduced without increasing blood loss.