J Korean Soc Spine Surg.  2004 Dec;11(4):202-209.

Optimal Trajectories of C1 Lateral Mass Screws and C2 Pars-Pedicle Screws

• Yeom JS
• Kwon YJ
• Yoo SM
• Park SK
• An YH
• Park KW
• Song KS
• Lee DH
• Kim HM
• Kim CY
• Chang BS
• Lee CK

Abstract

STUDY DESIGN: Surgical simulation using CT images of the cervical spine and computers.
OBJECTIVES
The optimal trajectories for C1 lateral mass screws and C2 pars-pedicle screws were sought, and their accuracy evaluated. LITERATURE REVIEW SUMMARY: There have been a few suggestions for the trajectories of the screws listed above, but these are somewhat vague or impractical.
MATERIALS AND METHODS
Using 1 mm-sliced CT scan images of 128 patients, and a V-works spine surgery simulator 4.0 (Cybermed, Inc., Korea), the optimal trajectories with which 4.0 mm screws can be inserted without breaching bone cortices were determined. The anatomical characteristics of the cases having a cortical perforation were analyzed.
RESULTS
The insertion point suggested for a C1 screw was 1 mm lateral to the middle of the junction of the posterior arch and posterior inferior part of the lateral mass. The screw was directed 15 degrees medially and toward the junction of the superior 2/3 and inferior 1/3 of the anterior tubercle in the lateral fluoroscopic view. The C2 screw was directed 30 degrees medially, and toward the anterior end of the superior articular process, in the lateral fluoroscopic view. The insertion point was one where the screw was inserted close to the superomedial border of the pedicle. Using these trajectories, all (256/256) of the C1 screws were inserted safely. However, 6.3% (16/256) of the C2 screws breached the inferolateral cortices of the pedicles, due to the pedicles being either too narrow or too medially angulated.
CONCLUSIONS
Herein, more practical and safe screw trajectories have been suggested. Using these trajectories, all the C1 and most of the C2 screws were able to be inserted safely. However, there were some cases in which the C2 screws could not be inserted without breaching the vertebral artery groove. Therefore, preoperative thin-slice CT scanning, with three-dimensional reconstruction and/or three-dimensional CT-angiography, is recommended for these cases.

Keyword

C1-2 screw fixation; C1 lateral mass screw; C2 pars-pedicle screw; computer simulation

MeSH Terms

Computer Simulation
Humans
Spine
Tomography, X-Ray Computed
Vertebral Artery

Figure

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  Fig. 1. Trajectories of lateral mass screws of C1 are shown. (A) Traditional multiplanar reformatting (MPR) images and a posterior view of a three-dimensional image are shown. (B) Trajectory MPR images and a lateral view of a three-dimensional image are shown. (C) Traditional MPR images and an anterior view of a three-dimension-al image are shown.

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  Fig. 2. Trajectories of parspedicle screws of C2 are shown.(A) Traditional MPR images and a superoposterior view of a three-dimensional image are shown. (B) Traditional MPR images and a superoposterior view of a three-dimensional image are shown. (C) Trajectory MPR images and an anterior view of a three-dimensional image are shown.

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  Fig. 3. A virtual fluoroscopic image shows the trajectories of C1 and C2 screws in lateral view.

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