Elsevier

The Spine Journal

Volume 13, Issue 7, July 2013, Pages 775-785
The Spine Journal

Clinical Study
Risk of vertebral artery injury: comparison between C1–C2 transarticular and C2 pedicle screws

https://doi.org/10.1016/j.spinee.2013.04.005Get rights and content

Abstract

Background context

To our knowledge, no large series comparing the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.

Purpose

To compare the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.

Study design

Radiographic analysis using CT scans.

Patient sample

Computed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.

Outcome measures

Cortical perforation into the vertebral artery groove of C2 by a screw.

Methods

We simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤5 mm or internal height ≤2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤4 mm on axial images).

Results

There were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).

Conclusions

Overall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.

Introduction

Evidence & Methods

Whether transarticular or pedicle screws (at C1–C2) pose greater risk to the vertebral arteries is unclear.

In this computer simulation using actual patient CT scans, the authors found no difference in risk between the two techniques unless a high-riding vertebral artery was noted, in which case pedicle screws appear safer.

The study provides valuable information that might help improve safety for patients.

—The Editors

Posterior C1–C2 transarticular screw fixation can result in vertebral artery injury, with potentially catastrophic results such as vertebrobasilar insufficiency, brain stem and posterior fossa infarct, and even death [1], [2], [3]. The rate of vertebral artery injury has been reported to be as high as 8.2% [1], [2], [3]. Vertebral artery injuries commonly occur if a drill, tap, or screw perforates or occludes the vertebral artery in the vertebral artery groove of C2, which is located on the lower surface of C2 and lateral to the pedicle (Fig. 1) [1], [2], [3], [4], [5], [6], [7], [8]. It has been suggested that C2 pedicle screw combined with C1 lateral mass screw placement is inherently safer than C1–C2 transarticular screw fixation in view of the risk of vertebral artery injury at C2, as the medially directed trajectory of the C2 pedicle screw carries the screw away from the vertebral artery, which normally is located lateral to the screw [9], [10], [11]. Although this is a commonly held belief, no large series have been performed to assess the validity of this assumption. Knowing whether the risk of vertebral artery injury is higher with C1–C2 transarticular screw fixation versus C2 pedicle screw placement is important, as the knowledge would provide surgeons with information on which to choose the appropriate fixation method, particularly in cases where the anatomy may be abnormal (eg, in the cases of a high-riding vertebral artery or narrow pedicle).

To date, two reports comparing the risk of vertebral artery injuries by transarticular screw versus pedicle screw have been published [12], [13]. Both studies stated that the anatomic risk of vertebral artery injury is not significantly different between transarticular and pedicle screws, contrary to the previous suggestion favoring pedicle screw [9], [10], [11]. Although these studies carefully analyzed the risk of each fixation method, like all studies, they have limitations. One study [13] used mainly 2D images with three-dimensional (3D) images used only in 10 patients. As stated by Miyata et al. [14], a 3D evaluation is essential for establishing the anatomic relationship between the course of the vertebral artery and the intended screw trajectory. Furthermore, both studies analyzed a small number of patients without a power analysis, raising the possibility that they were underpowered to detect a difference between the two fixation methods (beta error).

In addition to analyzing the safety of each technique in the general patient population, it may be even more important to evaluate the risk of vertebral artery injury in those with a relatively small space to accommodate these screws. These are the individuals in whom the risk of vertebral artery is increased, and the choice of appropriate screw fixation is even more important. Two anatomic variations have been suggested to be associated with vertebral artery injury. First, it is well known that the risk of vertebral artery injury during C1–C2 transarticular screw placement increases with a high-riding vertebral artery [2], [5], [6], [15], [16]. However, we are unaware of any reports comparing the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw in those with a high-riding vertebral artery, and no references on the topic could be found in a computerized search using MEDLINE. Second, narrow pedicles of C2 theoretically can increase the risk of vertebral artery injury by C2 pedicle screw. Yoshida et al. [12] stated in their 3D simulation study that pedicle screw placement was limited by the width of the C2 pedicle. However, again, as far as we know, no studies have been performed comparing the risk of vertebral artery injury with transarticular screw versus pedicle screw in those with a narrow pedicle.

Given the limitations of the existing studies, the primary purpose of our study was to compare the anatomic risk of vertebral artery groove violation by transarticular screw versus pedicle screw using a large number of computed tomography (CT) scan images and 3D screw trajectory simulation software. The comparison was performed in three groups of patients: the overall patient population and two subsets, those with a high-riding vertebral artery and those with narrow pedicles. Of note, neither C1–C2 transarticular screws nor C2 pedicle screws are approved by the US Food and Drug Administration.

Section snippets

Materials

This study was approved by our institutional review board. Computed tomography scans (Mx8000 IDT; Philips Medical Systems, Best, The Netherlands) of the cervical spine of consecutive patients taken at a single institution between March 2007 and June 2008 were initially included for the analyses. All the CT scans taken in 1.0-mm intervals were initially included regardless of the indications for the scan or the diagnosis. Exclusion criteria included CT scans of the patients under 20 years of

Demographic data

Computed tomography scans of 269 consecutive patients who fulfilled the selection criteria were used in the study, for a total of 538 possible screw insertion sites. There were 159 men and 110 women and the age averaged 49 years (range 20–84 years).

Frequency of high-riding vertebral artery and narrow pedicle

There were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%) among the 538 possible screw insertion sites. The vast majority of narrow pedicles (82%, 42/51) had a concurrent high-riding vertebral artery, whereas only 54% (42/78)

Discussion

Placement of either C1–C2 transarticular or C2 pedicle screws has a potential risk of vertebral artery injury [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [21]. The risk of vertebral artery injury by these two techniques needs to be carefully analyzed so as to allow the surgeon to choose the appropriate screw insertion method. Whereas some surgeons [9], [10], [11] have suggested that C2 pedicle screws have theoretical advantages over C1–C2 transarticular screws, as

Conclusions

To our knowledge, this is the only study that specifically compares the risk of vertebral artery injury by C1–C2 transarticular screws versus C2 pedicle screws using a sufficiently large number of cases based on a power analysis for sample size estimation. In addition, we are also the first to evaluate the risk of vertebral artery injury by both types of screws in those with a high-riding vertebral artery and/or narrow pedicle. This study reveals that, overall, neither technique has an

Acknowledgments

This study was supported by a Research Grant (04-2008-006) of Seoul National University Bundang Hospital of JSY (04-2008-006) with US $9,000. This is a pure academic grant, and there are no topic-specific potential conflicts of interest with this study. KDR receives royalties for a posterior cervical fixation system, which can be used for C1–C2 transarticular or C2 pedicle screws; however, this system neither is mentioned in this article nor was used during the study. We thank and acknowledge

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    FDA device/drug status: Not approved (C1–C2 transarticular and C2 pedicle screws).

    Author disclosures: JSY: Grant: Research Grant of Seoul National University Bundang Hospital (04-2008-006) (B); Speaking/Teaching Arrangements: Medtronic (B), DePuy (B). JMB: Consulting: Stryker, Inc. (B), CoreLink, Inc. (B), Globus Medical, Inc. (C), Medtronic, Inc. (B); Speaking/Teaching Arrangements: Stryker, Inc. (C), Globus Medical, Inc. (B), K2M, Inc. (B), DePuy, Inc. (B); Trips/Travel: International Spine Study Group (ISSG) (B, Reimbursement for travel accommodations only); Complex Spine Study Group (B, Reimbursement for travel accommodations only); AO Spine (B, Reimbursement for travel accommodations and honoraria); Broadwater, Inc. (B, Honoraria). H-JK: Nothing to disclose. B-SC: Stock Ownership: Bio Alpha, Inc. (B). C-KL: Nothing to disclose. KDR: Royalties: Biomet (F); Medtronic (G), Osprey (D); Stock Ownership: Expanding Orthopedics (C); Private Investments: Amedica (C), Benvenue (C), Nexgen Spine (B), Osprey (C), Paradigm Spine (C), PSD (C), Spinal Kinetics (C), Spineology (C), Vertiflex (C); Trips/Travel: AOSpine (Honorarium B), New England Spine Society Group (Honorarium A), Dubai Spine Society (reimbursement only), SpineMasters (reimbursement only), Broadwater (reimbursement and ski lift tickets); Board of Directors: AOSpine (E); Research Support (Investigator Salary): AOSpine (Lab & Materials, Paid directly to institution/employer), Cerapedics (Laboratory and Materials, Paid directly to institution/employer), Spinal Dynamics (Laboratory and Materials, Paid directly to institution/employer); Research Support (Staff/Materials): AOSpine (Lab & Materials, Paid directly to institution/employer), Cerapedics (Lab & Materials, Paid directly to institution/employer), Spinal Dynamics (Lab & Materials, Paid directly to institution/employer); Grants: Medtronic Sofamor Danek (for IDE participation, Paid directly to institution/employer); Fellowship Support: AOSpine (E, Paid directly to institution/employer), OREF (D, Paid directly to institution/employer).

    The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

    Institutional review board status: This study received the approval of the institutional review board of Seoul National University Bundang Hospital.

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