Sat., 10/10/09 Basic Sci./Injury Prevent./Spine, Paper #78, 12:04 pm OTA-2009
Posterior C2 Instrumentation in the Management of Trauma: Accuracy and Risks Associated with Four Techniques
Richard J. Bransford, MD1 (4,7-AO; 4,5A,7-Synthes; 7-Biomet, Pfizer, Wright Medical
Technology, Inc., DePuy, A Johnson &Johnson Company, Spinevision, Stryker);
Anthony J. Russo, MD2 (n); Mark Freeborn, MD1 (n); Quynh Nguyen, PA-C1 (n);
Michael J. Lee, MD1 (4, 7-Synthes, Zimmer); Jens R. Chapman, MD1 (4, 7-Medtronic Sofamor Danek; 4, 5A, 7, 10-Synthes, USA; 5B, 7-DePuy, A Johnson &Johnson Company; 5B-Alseres Pharmaceuticals, Paradigm Spine; 5B, 7, 10-Stryker; 7-HansJoerg Wyss Foundation);
Carlo Bellabarba, MD1 (2-JOT; 4-Smith &Nephew; 7-Synthes, AO Spine, DePuy, A Johnson &Johnson Company);
1Harborview Medical Center / University of Washington, Seattle, Washington, USA;
2Montana Orthopaedics, Butte, Montana, USA
Purpose: Posterior instrumentation of C2 is important in treating occipitocervical, atlantoaxial, and subaxial spinal injuries. The widely variable C2 anatomy can make instrumentation challenging and prone to potentially severe and even life-threatening complications, such as vertebral artery or neurologic injury. The goals of this study were (1) to evaluate a large series of posterior C2 screws in order to determine accuracy as assessed by CT scan, (2) assess dimensions of “safe bony windows” with CT, and (3) assess the perioperative complication rate related to errant screw placement. We hypothesized that the evolution of a greater variety of options for C2 fixation and the ability to tailor these techniques to patients’ specific anatomy has resulted in decreased complications and increased accuracy.
Methods: A retrospective review of a single tertiary care referral center spine database was assessed to identify all patients with operative management for traumatic conditions with C2 instrumentation between December 2002 and September 2008. Clinical data were obtained from the electronic medical record. Radiographic analysis included evaluation of pre- and postoperative CT scans to quantify the patients’ bony anatomy as well as to classify the accuracy of C2 screw placement. All C2 screws were graded using the following definitions: type I (ideal placement), screw threads completely within the bony cortex; type II (acceptable placement), less than one-half the diameter of the screw violates the surrounding cortex; and type III (unacceptable placement), clear violation of the transverse foramen or spinal canal.
Results: 169 patients (99 male and 70 female) underwent posterior C2 screw fixation for traumatic conditions of the spine during this time fram,e including 23 atlanto-occipital dissociations, 16 unstable C1 ring injuries, 79 dens fractures, 9 hangman’s fractures, 8 other C2 fractures, 3 C2 hyperextension injuries, 4 C2-C3 flexion-distraction injuries, 14 subaxial injuries, and 19 odontoid nonunions. Average CT measurements of pedicle height, axial width, and laminar width were 8.1 mm (SD 2.1 mm), 5.8 mm (1.9 mm), and 5.7 mm (1.5 mm), respectively, with males having larger pedicle height (P <0.001), pedicle width (P <0.001), and laminar width (P <0.022).
169 patients with 324 screws underwent CT analysis and chart review. 169 pedicle, 85 transarticular, 50 laminar, and 20 short pars screws were placed with 80.6%, 84.4%, 96%, and 94.4% accuracy rates (grade I vs II and III), respectively. Overall, 85% of screws were rated as being in the ideal location. 20 patients (40 screws) did not have postoperative CT scans and were not included for analysis of accuracy. Per clinical records, there were no cases of known vertebral artery injury at the time of surgery. Two pedicle screws were unacceptably placed (grade III). Both patients had screws encroaching on the vertebral artery foramen; one patient had a vertebral artery occlusion and the other had a grade I dissection documented on CT angiogram without clinical signs of stroke or emboli as measured on transcranial Doppler. No neurologic injuries resulted from instrumentation.
Conclusion: Our findings demonstrate a lower than previously reported incidence of complications associated with posterior C2 screw placement. In the management of 169 patients with 324 screws, only 2 patients had vascular injuries, as documented by CT angiogram; neither had any sequalae. The multiple techniques of posterior C2 fixation that are currently available allow for unprecedented flexibility in determining which technique is best suited for a given patient’s anatomy. Anatomical dimensions need to be carefully assessed preoperatively and may help determine which technique is ideal.
Disclosure: (n=Respondent answered 'No' to all items indicating no conflicts; 1=Board member/owner/officer/committee appointments; 2=Medical/Orthopaedic Publications; 3=Royalties; 4=Speakers bureau/paid presentations; 5A=Paid consultant or employee; 5B=Unpaid consultant; 6=Research or institutional support from a publisher; 7=Research or institutional support from a company or supplier; 8=Stock or Stock Options; 9=Other financial/material support from a publisher; 10=Other financial/material support from a company or supplier).
• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant