Subaxial cervical pedicle screw placement using limited opening technique: experimental study and preliminary clinical report

Abstract

Objectives To evaluate the safety and accuracy of limited opening technique for traspedicular screw placement in subaxial cervical spine. Methods Twenty fresh cervical specimens (C_3-C_7) were included in this study and placed with 199 pedicle screws using limited open technique for evaluation of the location of the screws. Forty C_3-C_4 specimens (80 sides) were used to observe architec-ture of the cervical pedicle and measure parameters related with screw placement. Seven patients with cer-vical instability were treated with pedicle screw fixation (29 screws) using this limited open technique.The cancellous bone in the junction of lateral mass and medical wall of pedicle was removed to find the in-let of the pedicle. The pedicle screws were inserted according to the measurement results of CT and X-ray. The patients were then evaluated radiographically for the location of the pedicle screw. Results The key structure safely leading into the pedicle was the junction between deep cortex of C_3、C_4 lateral mass and medial wall of the pedicle, which was located at the lateral upper quadrant of the lateral mass,with hard contour surface but without nutrient foramens. The screw insertion points were distributed at lat-eral upper quadrant of the lateral mass, with mean debouchement diameter of 5.2 mm, mean inlet width of 7.5 mm, medial angle of 42°and upward angle of 10°. The accuracy rate of screw placement was 94.5% in specimens and 100% in patients. Conclusion Limited opening at lateral mass surface combined with single-blade blunt end probe is proved to be a safe and accurate technique for subaxial cer-vical pedicle screw placement. Key words: Cervical vertebrae; Fracture fixation,internal; Limited opening technique