Accuracy and complications associated with posterior C1 screw fixation techniques: a radiographic and clinical assessment.

BACKGROUND CONTEXT: The variable C1 anatomy can make instrumentation challenging and prone to potentially severe complications. New techniques have expanded available options.

PURPOSE: The aims of this study were to evaluate a large series of posterior C1 screws to determine accuracy by computed tomography (CT) scan; assess dimensions of "safe bony windows" with CT; and assess perioperative complication rate related to errant screw placement.

STUDY

DESIGN

Retrospective review of a single tertiary care spine database to identify patients with C1 instrumentation between December 2002 and September 2008.

PATIENT SAMPLE: The sample comprised 176 patients with 344 C1 screws. All 176 patients were assessed for perioperative complications related to their C1 screws. Twenty-nine patients did not have postoperative CT scans, leaving 147 patients with 286 screws for analysis of screw accuracy.

OUTCOME MEASURES: The outcome measures consisted of a radiographic assessment of accuracy of placement of C1 instrumentation and a clinical assessment of perioperative complications related to C1 instrumentation focusing on neurologic and vascular injuries.

METHODS

Clinical data were obtained from the medical record. Radiographic analyses included preoperative and postoperative CT scans to quantify the patients' bone and classify accuracy of instrumentation. Screws were graded using the following definitions: Type I, screw threads completely within the bone; Type II, less than half the diameter of the screw violates the surrounding cortex; and Type III, clear violation of transverse foramen or spinal canal.

RESULTS

One hundred seventy-six patients (97 males and 79 females) underwent posterior C1 screw (lateral mass [LM] or transarticular [TA]) fixation. A total of 344 screws were placed with 216 LM screws and 128 TA screws. Twenty-nine patients (58 screws) did not have postoperative CT scans and were not included for analysis of radiographic accuracy but were included in assessment of complications based on medical records. Ninety-six percent of screws (Type I or II) were rated as "safe," and 86% of screws were rated as being ideal (Type I). Twelve screws (4%) were unacceptably placed (Type III). There were no known neurologic or vertebral artery injuries. One patient underwent revision surgery for a medially placed screw. Mean C1 LM width was 10.5 mm across all patients. Estimated blood loss averaged 331 mL.

CONCLUSIONS

Our findings demonstrate a low incidence of complications associated with posterior screw instrumentation of the C1 LM.