Accuracy of cervical pedicle screw placement using the funnel technique

Study Design. This was a cadaver study assessing the accuracy of cervical p edicle screw placement. Objective. To evaluate the accuracy of the funnel technique of screw placem ent. Summary of Background Data. Although excellent results have been reported i n clinical studies, with no major neurovascular injuries, several cadaveric studies have shown a high pedicle perforation rate during screw placement. Methods. Ten fresh frozen cervical spines (C2-C7) were used (120 pedicles, 20 pedicles per level). The average specimen age was 79.6 years (range 65-9 7); the average height was 159 cm (range 155-175). The male-to-female ratio was 3:7. Pedicle width and angulation were measured on preoperative axial computed tomography (1-mm slices). By use of four bony landmarks and the fu nnel technique, screws were placed under direct vision. Critical perforatio ns (documented contact of a screw with, or an injury to, a spinal cord, ner ve root, or vertebral artery) and noncritical perforations (a perforation w ith no critical contact) were recorded. Results. In seven pedicles (5.8%) the procedure was aborted because of a sm all or nonexistent pedicle medullary canal. Ninety-four pedicle screws (83. 2%) were placed correctly, whereas 11 pedicles (9.7%) had noncritical perfo rations and 8 pedicles (7.1%) had critical perforations. The majority of th e critical and noncritical perforations were at C3, C4, and C5. Conclusions. Axial computed tomography is necessary for the preoperative pl anning. Because of the small diameter and steep angulation of cervical pedi cles, every spine surgeon who intends to use pedicle screws should first ma ster the technique on cadavers.