Study Design. Retrospective review of a single tertiary care spine database to identify patients with C2 instrumentation between January 2001 and September 2008.
Objective. (1) Evaluate a large series of posterior C2 screws to determine accuracy by computed tomography (CT) scan, (2) assess dimensions of “safe bony windows” with CT, and (3) assess perioperative complication rate related to errant screw placement.
Summary of Background Data. The variable C2 anatomy can make instrumentation challenging and prone to potentially severe complications. New techniques have expanded available options.
Methods. Clinical data were obtained from the medical record. Radiographic analyses included preoperative and postoperative CT scans to quantify the patients’ bone and to classify accuracy of instrumentation. Screws were graded using the following definitions:
Type I: Screw threads completely within the bone.
Type II: Less than (1/2) the diameter of the screw violates the surrounding cortex.
Type III: Clear violation of transverse foramen or spinal canal.
Results. Seven hundred and thirty-six screws in 383 patients were identified. Fifty-five patients were excluded because of lack of data leaving 328 patients (188 male patients, 140 female patients) with 633 screws. Three hundred and thirty-nine pedicle, 154 transarticular, 63 laminar, and 77 short pars screws were placed, and of the 509 screws with postoperative CT scans, accuracy rates (Types I and II) were 98.8%, 98.5%, 100%, and 94.6%, respectively. Eight were unacceptably placed: two medially and six encroaching on the vertebral artery foramen. One patient had a vertebral artery occlusion and another had a dissection. There were no neurologic injuries. Mean CT measurements of pedicle height, axial width, and laminar width were 8.1, 5.8, and 5.7 mm respectively, with males having significantly larger pedicle height (P < 0.001), pedicle width (P < 0.001), and laminar width (P < 0.022).
Conclusion. We show a lower than previously reported incidence of complications associated with posterior C2 screw placement. The multiple techniques of posterior C2 fixation available allow for flexibility in determining ideal technique.
This retrospective study of 633 screws placed in 328 patients shows an accuracy rate of 98.4% with 339 pedicle screws, 154 translaminar screws, 77 short pars screws, and 63 laminar screws. The current techniques allow for flexibility, a decreased complication rate, and an increased accuracy than has been previously reported.
From the *Department of Orthopaedics and Sports Medicine, Harborview Medical Center/University of Washington Medical Center, Seattle, WA
† Montana Orthopaedics, Butte, MT
‡ Evergreen Orthopaedic Center, Kirkland, WA
§ Department of Radiology, Harborview Medical Center, Seattle, WA
Address correspondence and reprint requests to Richard Bransford, MD, Harborview Medical Center, Department of Orthopedics and Sports Medicine, Box 359798, 325 9th Avenue, Seattle, WA. E-mail: firstname.lastname@example.org
Acknowledgment date: June 2, 2010. First revision date: September 8, 2010. Acceptance date: September 13, 2010.
The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.
No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
University of Washington IRB Approval #35367.
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.