Clinical Neurology and Neurosurgery 125 (2014) 24–27 Contents lists available at ScienceDirect Clinical Neurology and Neurosurgery jo ur nal homep age: www.elsevier.com/lo cate/clineuro Accuracy of C2 pedicle screw placement using the anatomic freehand technique Mohamad Bydon a,b,1 , Dimitrios Mathios a,b,1 , Mohamed Macki a,b , Rafael De la Garza-Ramos a,b , Nafi Aygun c , Daniel M. Sciubba a , Timothy F. Witham a , Ziya L. Gokaslan a,b , Ali Bydon a,b,∗ , Jean-Paul Wolinksy a a Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, USA b Johns Hopkins Spinal Biomechanics and Surgical Outcomes Laboratory, Baltimore, USA c Department of Neuroradiology, Johns Hopkins University School of Medicine, Baltimore, USA a r t i c l e i n f o Article history: Received 31 May 2014 Received in revised form 30 June 2014 Accepted 13 July 2014 Available online 20 July 2014 Keywords: C2 Cervical Freehand Pedicle Screws a b s t r a c t Objective: The objective of this study is to evaluate the incidence and prognostic factors of breach rates following the placement of C2 pedicle screws using the anatomic, freehand technique. Methods: We retrospectively reviewed the medical records of all patients who underwent C2 transpedic- ular instrumentation over six years at a single institution. All intraoperative, image-guided techniques were excluded. Breaches were ascertained from immediate postoperative CT images. All images were analyzed by three independent reviewers. The screw length was correlated with (1) the breach rate and (2) the breach severity. Severity of the breached screws reflects the screw circumference (0–360 ◦ ) perforating the pedicle wall (Grade 1–Grade 4). Results: Of the 341 C2 pedicle screws inserted in 181 patients, the average screw length was 22.93 ± 3.7 mm. The average distance from the foramen transversarium to the screw insertion point was 13.17 ± 2.63 mm. The distance from the medial rim of the pedicle to the dura of spinal cord was 3.53 ± 1.57 mm. Of the 341 screws, the overall breach rate was 17.3% (n = 59). Of the 59 breaches, 89.83% of screws (n = 53) breaching the spinal canal was statistically significantly higher than the 10.17% of screws (n = 6) breaching the foramen transversarium (p < 0.001). Moreover, 27 (45.8%) were Grade 1, 16 (27.1%) Grade 2, 6 (10.2%) Grade 3, and 10 (16.9%) Grade 4. None of the C2 breaches resulted in neurolog- ical sequela. No association was found between breach rate and gender, race or age. While the average screw length was 22.93 ± 3.7 mm [12–34 mm], screw length did not predict a cortical violation (p = 0.4) or severity of the breach (p = 0.42) in a multiple regression model. Conclusions: In this cohort study on the anatomic freehand placement of C2 pedicle screws, the breach rate was 17.3%. Lateral breaches were more common than medial breaches. Screw length was not statistically correlated with cortical violation or severity of breach. Therefore, screw length is not a prognostic factor for C2 pedicle screw misplacement. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Instrumented fusion of the C2 spinal level is technically chal- lenging, owing to the anatomical complexity of the upper cervical ∗ Corresponding author at: Corresponding author at: Johns Hopkins School of Medicine, Department of Neurosurgery, 600 N Wolfe St. Meyer 7-109 Baltimore, MD 21205, USA. Tel.: +1 443 287 4934; fax: +1 410 502 3399. E-mail addresses: mbydon1@jhmi.edu (M. Bydon), abydon1@jhmi.edu (A. Bydon). 1 These authors contributed equally to this manuscript. spine. In 1992, Jeanneret and Magerl described the transarticular screw fixation of the atlantoaxial joint [1,2]. In 1994, Goel et al. first described the posterior plate and screw fusion technique in the atlantoaxial fusion [3]. In 2001, Harms and Melcher popularized the placement of minipolyaxial screws into the C2 pedicle [4]. In the Harms technique, the C2 pedicle screws caudally communicated with the C1 lateral mass screws rostrally via a rod-cantilever con- struct. Today, C2 pedicle screws have become an important adjunct to the arthrodesis of the atlantoaxial joint. Although the safety pro- file of C2 pedicle screws has been well established in the literature [5], freehand placement of these pedicle screws is not without its risk of intraoperative complications. http://dx.doi.org/10.1016/j.clineuro.2014.07.017 0303-8467/© 2014 Elsevier B.V. All rights reserved.