Transpedicular lag screw placement in traumatic cervical spondylolisthesis: Case report and systematic review of the literature

Journal of Clinical Neuroscience 63 (2019) 256–262

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Tools and techniques

Transpedicular lag screw placement in traumatic cervical spondylolisthesis: Case report and systematic review of the literature Joshua Bakhsheshian, Saman Sizdahkhani, Ifije Ohiorhenuan, Ian A. Buchanan, Ben Strickland, Martin H. Pham ⇑ Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States

a r t i c l e

i n f o

Article history: Received 19 October 2018 Accepted 28 January 2019

Keywords: Hangman’s fracture Traumatic spondylolisthesis Cervical spine

a b s t r a c t Traumatic spondylolisthesis of C2-C3 is an unstable fracture. Posterior fixation techniques can be employed with intraoperative navigation, however this tool is not available to all spine surgeons. Furthermore, the evidence for posterior surgical stabilization of C2, while adhering to motion preservation principles is currently unknown. The authors describe a patient who had fractures of the pedicle and vertebral body of C2 and C3, which was successfully stabilized with freehand placement of C2 pedicle lag screws and subsequent C2-C5 fixation. Subsequently, a systematic review was performed to evaluate studies that utilized C2 lag screw placement in patients with traumatic spondylolisthesis of the axis (TSA). Eight retrospective case series were identified (N = 63 patients). Five studies evaluated an open posterior cervical approach and 3 investigated a percutaneous approach. Follow-up time ranged from 2 to 48 months and fusion was successful in most cases. No intra-operative complications were reported. On final follow-up, 2 patients had unintentional C2-C3 fusion, and 3 had C2-C3 instability. Three minor complications (urinary tract infection, surgical site hematoma, respiratory infection) were also reported, that resolved with medical management. Freehand placement of C2 pedicle lag screws may be a viable option in select cases. While posterior C2 lag-screw fixation demonstrated successful fusion in most patients with TSA, the supporting evidence is limited to level IV studies. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Traumatic spondylolisthesis of the axis (TSA) can occur with severe hyperextension and distraction and commonly involves bilateral fractures of the C2 pars interarticularis. While some TSAs may be treated with rigid external fixation, the unstable fracture types warrant surgical intervention [1–3]. Numerous classification systems have attempted to assess the instability of the different types of TSA to help guide management decisions, but each have their own limitations. [3–8] The classification system by Levine and Edwards (LE) is most commonly used, and categorizes the fracture based on the degree of displacement (angle of convergence of inferior end plates of C2 and C3) and translation of C2 and C3 vertebral bodies [5]. The LE classification also incorporates the postulated mechanism of injury (Table 1). If the fracture is deemed

Abbreviations: TSA, spondylolisthesis of the axis; LE, Levine and Edwards; CT, computed tomography. ⇑ Corresponding author at: LAC+USC Medical Center, 1200 North State Street, Suite 3300, Los Angeles, CA 90089, United States. E-mail address: [email protected] (M.H. Pham). https://doi.org/10.1016/j.jocn.2019.01.036 0967-5868/Ó 2019 Elsevier Ltd. All rights reserved.

unstable, a continuum from cervical traction to surgical fixation for internal stabilization is recommended [3,9–11]. However, given the heterogeneity of the fracture pattern, and degree of instability that may extend from C2-C3, the optimal surgical strategy is not straightforward. Reduction of the fractured segments in TSA with direct posterior fixation can be challenging. Furthermore, pedicle screw placement in C2 is a technically demanding approach, and can carry an appreciable risk for neurovascular complications [12]. The utilization of partially threaded screws, also known as lag screws, has been reported to promote C2 vertebral body reduction and fusion success [3,9]. Prior reports on C2 transpedicular fixation for hangman’s fractures have relied on intraoperative image guidance for pedicle screw placements [9,11,13,14]. However, freehand placement of C2 pedicle screws can be placed safely in select circumstances [12,15]. To the authors’ best knowledge, posterior screwrod fixation combined with freehand placement of C2 lag screws for TSA has not been previously reported. In the following report, we present a patient with C2-C3 pars-interarticularis, pedicle and vertebral body fractures that underwent posterior screw rod-

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Table 1 Summary of Levine and Edwards classification system, adapted from Levine and Edwards 1985. Fracture patterns categorized based on displacement, degree of angulation (angle of convergence of inferior end plates of C2 and C3) and caliber of vertebral body translation; it also takes into account the postulated mechanism of injury. (19). Type I

Type II

Type IIa

Type III

Displacement Angulation Translation Mechanism

Non-displaced No angulation <3 mm translation Hyperextension-axial loading

Displaced Angulation (0–25°) Slight or no translation flexion-distraction

Severe displacement significant angulation (8–25°) 3 mm of translation flexion-compression

Stability

Stable: able to assess w/physician monitored flexion/ extension radiographs Philadelphia collar with cement vs. halo

Displaced Angulation (0–25°) 3 mm of translation hyperextension-axial loading with secondary flexion-compression Unstable: associated w/significant wedge compression of the antero-superior portion of the C3 vertebral body Philadelphia collar vs. cervical long traction with halo

Unstable: no associated wedge compression as seen in Type II Reduction via cervical compression/ extension under fluoroscopy

Unstable: unilateral or bilateral facet dislocations at C2 or C3

Treatment

fixation of C2-C5 with freehand placement of C2-pedicle lag screws and C3-C5 lateral mass screws. Furthermore, a systematic review of prior studies investigating the posterior placement of C2 lag screws technique was performed. 2. Case report

Initial halo for reduction of facet dislocation followed by surgical stabilization

ray (Fig. 1). Computed tomography (CT) of the cervical spine demonstrated fracture pattern to include C2 and C3 pars interarticularis and pedicles, while extending into the posterior vertebral bodies (Fig. 2). CT angiography was unremarkable. MRI of the cervical spine was notable for posterior longitudinal ligament (PLL) disruption at C2-C3, without cranial cervical junction ligamentous disruption (Fig. 3).

2.1. Presentation A 32 year-old gentleman without any significant past medical history presented to the emergency room after losing control of his bicycle, which caused him to fall onto his head. The patient immediately experienced excruciating neck pain that was exacerbated with movements, and denied any radiating symptoms. The patient was neurologically intact on examination. Fractures of the C2 and C3 pars interarticularis was observed on cervical X-

2.2. Assessment The C2 (classified as LE Type IIa or Benzel Type 1: vertical and coronal orientation of C-2 body fracture), and C3 fracture pattern with ligamentous complex disruption was deemed unstable. Halo-vest orthosis was placed for immediate stabilization. Given instability of fractures at C2-C3, a C2-C5 posterior spinal instrumentation was planned. The C2 pedicles were evaluated to rule out a high-riding vertebral artery, and to approximate pedicle screw diameters and lengths for each side (making sure to subtract displaced gap from the final C2 screw length) based on preoperative CT imaging.

2.3. Technique

Fig. 1. X-ray imaging demonstrating fractures of the C2 and C3 pars interarticularis.

The patient was positioned prone under general anesthesia, with the halo-orthotic pins. A standard skin incision was made above the C2–C5 levels. The cervical spine was exposed in routine fashion. Lateral mass screws were placed bilaterally at C3-5 (3.5  16 mm screw) using a AO-Magerl technique [16]. A suitable point of entry at the superior and medial quadrant of the isthmus of C2 was selected for the placement of each C2 pedicle screw [12]. The screw path was carefully drilled from the entry point to the vertebral body through the fracture line. Given the frank instability of the fracture, drilling was performed in stages, taking care to intermittently verify the accuracy of the trajectory and to evaluate for breaches at multiple depths with a ball probe. The 2.4 mm drill was first used to drill a path into the C2 vertebral body. This was followed by the 2.9 mm drill to then ‘‘overdrill” just the C2 proximal bone up to the fracture site in a freehand fashion. This created a ‘‘gliding hole” for the unthreaded portion of the screw and allows for the desired lag effect to reduce the fracture. The left C2 pedicle screw (4.0  26 mm lag screw) was placed first, followed by the right side (4.0  30 mm lag screw), and were both tightened with a palpable sensation of reduction during placement. Significant movement of C2-C3 was observed during pedicle screw placement, confirming the instability of the C2-C3 complex. Lateral C-arm fluoroscopy was only used at the end to ensure the proper alignment of the detached elements of C2. Then, final screw-rod instrumentation and closure was completed in usual fashion.

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Fig. 2. Preoperative imaging demonstrating traumatic spondylolisthesis of C2 and C3. A: Preoperative axial CT scans showing C2 and C3 fractures. Corresponding axial and sagittal CT scans demonstrating longitudinal fracture patterns. Notably, the C3 fracture extends from the right pedicle through the left foramen transversarium. Minimal posterior displacement of the vertebral body fragments at the level of C2 and C3 was noted.

postoperatively. Immediate postoperative CT demonstrated reduction of the displaced segment (Fig. 4: top row), and osseous fusion was observed at fractured regions on 6 months follow-up CT (Fig. 4: bottom row).

3. Methods A systematic review of lag screws for type I or II Hangman fractures was conducted in the English literature over the last 10 years according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines [17]. An electronic search of the entire PubMed database (MEDLINE) of studies published between October 1, 2007 and October 1, 2017, was performed to identify studies

Fig. 3. Sagittal T2 MRI of the cervical spine demonstrating disruption of the posterior longitudinal ligament. However, there were no signs of spinal cord compression, disc disruption, or cranial cervical junction ligamentous disruption.

2.4. Postoperative course The patient experienced an uneventful post-operative recovery. At 3, 6 and 12-month follow-up visits he remained neurologically intact. The patient had some limitation in neck flexion/extension, otherwise denied significant difficulties with axial rotation (same as immediate postop). The patients reported visual analog score of 8 preoperatively reduced to 1 by 3 months and to 0 by 6 months

Fig. 4. CT imaging at immediate postop and 6-months follow-up demonstrating successful osseous fusion. Imaging after postoperative day 1 demonstrated reduction of the displaced fragment on the right and screw purchase across the displaced region with surgical fixation. At 6 months follow-up, CT imaging demonstrated osseous fusion across both pedicles in C2.

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that investigated outcomes of posterior lag screw fixation of C2 with goals of motion preservation. Any combination of the following search terms were used: traumatic type I Hangman fracture, traumatic type II Hangman fracture, traumatic spondylolisthesis of the axis, lag screws, threaded screws, posterior surgical approach, and posterior cervical fusion. The exclusion criteria consisted of: non-traumatic fractures (pathological), anterior surgical approach, conservative treatment only, threaded screws only, pediatric patients, and non-human studies. Included articles were categorized based on study type. Additional information gathered from each article includes the following: publication year, study type, number of patients, study population and mechanism of injury, assessment or outcome measures, and study conclusions. Once the articles were selected, the appropriate level of evidence was assigned to each study according to the Oxford Centre of Evidence Based Medicine levels of evidence [18–20]. When inclusion or exclusion was unclear based on title and abstract, full text articles were retrieved. In situations where reviewers did not agree, resolution occurred through discussion or the addition of a third reviewer if necessary.

4. Results The initial search yielded 306 articles, of which 8 were included (Fig. 5) [3,9,21–26]. The 8 articles were retrospective level 4 investigations and are summarized in Table 2. A total of 64 patients, including the present case were identified. Fifty-seven of the injuries were classified as the following: 47 LE Type II, 3 LE Type IIa, 4 LE Type III, and 3 Benzel Type I. Intra-operative image guidance was used in 7 studies, and not specified in 1 study [3]. Five studies investigated an open posterior surgical approach for lag screw placement [3,9,22,24,25]. Wang et al. reported the largest series found, which included 21 patients treated with open posterior C2-C3 pedicle screw fixation using C2 lag screws and a curved rod to aid in the reduction of the displaced C2 vertebral body intraoperatively [9]. Percutaneous placement of C2 pedicle or pars lag screws with intraoperative imaging guidance was investigated in 3 studies [21,23,26]. CT imaging and/or X-rays were used to assess post-operative fusion. No intra-operative complica-

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tions were reported. Mean follow up time ranged from 2 to 48 months and fusion was found in most studies, and not reported in 1 study [24]. Neurologic function improved in all cases. Neck pain generally improved with follow-up in all cases, except when unintended fusions occurred at C2-C3 with resulting cervical deformity and/or instability [25]. The majority of studies reported successful fusion with presumed motion preservation (Table 2).

5. Discussion Surgical stabilization of TSA has previously been shown to decrease the risk of nonunion while avoiding patient dissatisfaction associated with long-term rigid cervical collar and halo use [1,2]. While non-operative management can be employed in select stable isolated axis body fractures with short fracture displacement distances, associated instability at adjacent segments can significantly increase the risk for complications with a conservative approach [3,23]. TSA of both C2 and C3 is rare and can be very unstable [27]. This report discusses the unique case of surgical stabilization of traumatic spondylolisthesis of C2 and C3 in a patient who remained neurologically intact. C2 pedicle lag screw placement in TSA has been shown to benefit from overall stabilization with successful fusion. However, the evidence for this approach is limited to level IV studies. Complication rates were generally low, and varied based on associated injuries, initial neurological injury and specific patient comorbidities. Persistent instability has been shown in LE Type II fractures with >4.5 mm of translation which may have been due to preoperative disco-ligamentous injury at C2-C3 that was not identified prior to surgery [25]. Furthermore, Prior studies were conducted with the use of intraoperative navigation, a tool not available to all spine surgeons. Freehand placement of C2 lag screws may provide an alternative method for stabilization of TSA with preservation of motion at the occiput-C2 complex. The surgical approach for unstable TSA is determined based on the specific fracture pattern. For instance, the surgeon takes into consideration the degree of fracture displacement/angulation, extent of involvement in the pars interarticularis, pedicles, body, intervertebral discs, and ligamentous complex as well as the asso-

Fig. 5. Flow diagram showing selection of the studies for this systematic review.

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Table 2 Summary of the literature review. Eight studies are included in our systematic review results. The author and year, number of patients, character of the fracture, intra-operative image guidance, approach, post-operative fusion, follow up, results, neck pain, and complications are summarized. All studies are retrospective cohort studies providing level IV evidence. The ‘‘patients” column indicates the number of patients in the study total, and then identifies the subset that were applicable to the review based on injury type, age, or other inclusion/exclusion criteria. Injuries were documented based on study-specific descriptions. Author Year

Patients

Injuries

Image-Guidance

Approach

Fusion evaluation

Followup (months)

Results

Neck Pain

Complications

Kantelhardt 2012

16 Total, (5 included)

Iso-C3D

C2 pedicle screw, or with C3 lateral mass screw fixation

CT

5.9 (2–10)

Fusion not reported

None

None

Zhang 2014

28 Total, (4 included) 5 Total

2 isolated Hangman’s fractures, 3 w/C2-C3 instability 4 LE Type II

Not reported

C2 pedicle screw, or with laminar screws

CT

20.8

None

None

5 LE Type II

Iso-C3D

Percutaneous C2 pedicle screws

Lateral dynamic XR CT and dynamic XR CT

16.2 (12–18)

Fusion and normal ROM in all Fusion in all

None

None

None

Buchholz 2015

12

Fusion in all

2

Fusion in all

Improved (NDI 0–6% final) None reported

CT and dynamic XR

24 (12–36)

Fusion in all, JOA 17/ 17 in all

All with pain but improved

5 with C2-C3 fusion, 3 with C2C3 instability

Percutaneous pars screws

CT

3.5 (2.3–7.5)

Fusion in all

Improved

None

C2-C3 pedicle screws

CT and lateral XR

28 (15–48)

Fusion in all

Improved (VAS mean 1.2)

3 minor- UTI, hematoma, lung infection

Reynolds 2016

3 Total

3 Benzel Type 1

CT (O-arm)

C2 pedicle screw

Kantelhardt 2016

6 Total, (2 included) 11 Total

2 Hangman’s fractures

Iso-C3D

11 LE Type II

Fluoroscopy & K-wires, 2 with Neuronavigation Iso-C3D & Neuronavigation

Percutaneous C2 pedicle screws (unilateral) C2 ‘‘pars-pedicle” screws

Salunke 2016

Zeden 2017

12 Total

Wang 2017

21 Total

12 LE Type II, (2 with odontoid fractures) 15 Type II, 2 Type IIa, 4 Type III

C-arm fluoroscopy

ciated cervical spine fractures present. Lastly, the surgical plan is heavily dependent on the experience and technical skill of the surgeon. Surgical approaches can include anterior discectomy and fusion (C2-C3) or posterior fusion of varying levels, from occiput to C3 [3,9,28,29]. Given that most axial rotation of the head occurs in the upper cervical spine (occiput-C2), more recent surgical approaches have aimed to preserve the physiologic motion of the occipitoatlantoaxial complex by utilizing C2 pedicle screw fixation [9–11]. The goal of surgery was reduction, stabilization and arthrodesis. The presented patient was young, healthy, with good bone quality, and was neurologically intact. The patient had normal cervical alignment, and the trauma mainly disrupted the posterior tension band. With the aims of preserving motion at the occiput-C2 complex and stabilizing the unstable C2-C3 segment, a C2-C5 posterior fusion was performed. The authors acknowledge that a posterior fusion extending from C2-C4 could have been sufficient. The decision for selecting the number of inferior levels for instrumentation involved the minimal degree of vertebral body destruction and the use of lateral mass screws (instead of subaxial pedicle screws) [30,31]. Two-level pedicle screw fixation at C2-C3 would have provided additional biomechanical strength, thereby using a shorter construct. However, while subaxial cervical pedicle screws can provide additional biomechanical stability, they also carry greater risks for neurovascular injuries and many authors have advocated for place of these screws under navigation [30]. Placement of lateral mass screws (as described by Magerl and/or Roy-Camille) has been shown to provide sufficient biomechanical strength and carry a low risk for neurovascular injuries. Therefore, lateral mass screw-rod fixation was employed at C3 and two-levels inferior to the C3 fracture. Another viable option could have been a combined anterior-posterior approach for circumferential fixation at C2-C4. A posterior-only approach was employed with the intent of following the patient closely during the postoperative period and only recommending additional anterior fixation if it was deemed neces-

None

sary. Ultimately, anterior fixation was not required at final followup. As the dominant motion in the lower cervical spine is flexionextension, the patient expectedly reported some limitations in flexion/extension on postoperative follow-up. The surgical goals were accomplished in the presented case and the patient remained neurologically intact with no reported pain on 1-year postoperative follow-up. This report highlights the heterogeneity in the management of these fractures in the literature, while demonstrating that posterior C2 to C5 fusion can be considered for primary surgical treatment in select cases. Further high-powered studies are still needed to identify the optimal posterior fixation construct. 5.1. C2 pedicle lag screws Variability in the path of the vertebral artery, pedicle width and the shape of pars interarticularis can make C2 pedicle screw placement more difficult. These obstacles can be magnified in the trauma setting. The screw traverses a narrow pedicle bounded by the spinal cord, and the vertebral artery. Placement of C2 pedicle screws in patients with TSA have been successful with reported breach rates varying from 1 to 6.6% [10,11]. Partially threaded or lag screws have been employed in traumatic fractures given their ability to reduce wide fracture gaps and re-approximate detached posterior elements. In the included case report, successful fusion was achieved on follow-up even though the displaced fracture was not completely reduced intraoperatively. Prior investigations on C2 pedicle lag screw fixation for TSA relied on neuronavigation or intraoperative fluoroscopy guidance. The concern for injury to surrounding neurovascular structures is a crucial consideration. However, even under the guidance of intraoperative imaging guidance these complications can still occur undetected [24,32]. Furthermore, intraoperative spinal neuronavigation is not routinely available at all hospitals [33]. In 2013, a global survey demonstrated that approximately 11% of surgeons used

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spinal neuronavigation [34]. Härtl et al. found that intraoperative neuronavigation was not widely adopted on a global scale due to the lack of neuronavigation equipment, proper training, and associated high costs. In select circumstances, the freehand approach becomes more valuable, especially for rural areas or countries without routine access to imaging guidance. For hospitals without neuronavigation, the otherwise descriptive literature on intraoperative image guidance techniques is no longer applicable. Proper preoperative planning is required for successful placement of C2 pedicle screws. It is important to analyze the anticipated anatomy from preoperative CT and CTA of the cervical spine for surgical planning. Preoperative imaging can help identify patients with significant pedicle hypoplasia or high riding vertebral arteries that would significantly increase the risk for complications with this approach. Greater intraoperative exposure of the pars can facilitate safe freehand placement of C2 pedicle screws [12,15,35]. In 2009, Sciubba et al. retrospectively analyzed freehand placement of 100 C2 pedicle screws inserted in 55 patients, and found breaches in 15% that were not clinically significant [15]. In 2014, Bydon et al. retrospectively analyzed freehand placement of 341 C2 pedicle screws inserted in 181 patients, and found a breach rate of 17.3%, without clinical significance [35]. When breaches occur, they were mainly lateral and consisted of less than 50% of the screw diameter. These breaches rarely had a clinical consequence. Breach rates from C2 pedicle screw placement may be impacted by surgeon experience. In 2010, Alosh et al. evaluated 170 C2 pedicle screws placed in 93 patients, and while intraoperative fluoroscopy was used in 18 cases (19.4%), the authors found breaches in 43 (25.3%) cases with one left vertebral artery injury that was successfully treated with screw placement without clinical consequences [36]. The authors found that a pedicle diameter of less than 6 mm was associated with an approximately two-fold increase in risk of cortical breaches, and a trend that surgeons with more experience had lower breach rates. In 2018, Pham et al. retrospectively analyzed freehand placement of 40 C2 pedicle screws in 24 patients by neurosurgical trainees under the supervision of an experienced spine-fellowship-trained attending and found a breach rate of 17.5% that were without any clinical implications [12]. While C2 pedicle screws can be placed safely based on preoperative planning and extensive dissection for anatomical landmarks, intraoperative imaging still plays a vital role. This holds especially true for situations when anatomical landmarks are ambiguous or limited in minimally invasive approaches. Poor pre- and intraoperative planning could, however, negate the advantage of using intraoperative navigation. Therefore, intraoperative imageguidance should be used as an adjunct tool, with constant correlation of anatomical landmarks with corresponding image points, while acknowledging that it does not substitute for detailed knowledge of the anatomy, experience and judgment [33]. 5.2. Limitations This report is limited by the study design and does not demonstrate the superiority of one technique over other surgical options, or over conservative treatment. Rather, the report highlights our current understanding and supporting literature for the utilized technique. There is no consensus on a validated classification system for C2 fractures, likely due to heterogeneous C2-fracture patterns (classification crossover between axis body fractures, atypical hangman’s fractures, hangman’s fractures and may have concurrent odontoid type II or III fractures), which makes it more difficult to investigate. Classification systems are also limited on their basis of morphometric analysis of static imaging. Dynamic X-rays or MRI can provide more information, but they are not rou-

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tinely available or included in the reported studies. The majority of the literature on treating TSA reported fusion rates as their main outcome and this was not corroborated with other outcomes of interest including health-related quality of life measures, disability, range of motion and cervical mal-alignment. While direct fixation of TSA intends to preserve the occiput-C1–C2 motional characteristics, the actual impact on atlanto-axial rotation, articulation joints and cervicocephalic pain remains unclear. 6. Conclusion C2 lag screws may provide an alternative method for stabilization of TSA, while avoiding fusion of the occiput-C2 complex. Direct pedicle screw fixation with C2 pedicle lag screws is also feasible with a free-hand technique and may be utilized in the stabilization of TSA. This procedure is technically demanding and must be performed with extreme caution to avoid complications. Further robust studies are needed to investigate the impact on cervical motional characteristics and functional outcomes. 7. Compliance with ethical standards No funds were received in the support of this work. Conflict of interest 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. Acknowledgements None. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jocn.2019.01.036. References [1] Murphy H, Schroeder GD, Shi WJ, Kepler CK, Kurd MF, Fleischman AN, et al. Management of Hangman’s fractures: a systematic review. J Orthop Trauma 2017;31(Suppl 4):S90–5. [2] Shin JJ, Kim SH, Cho YE, Cheshier SH, Park J. Primary surgical management by reduction and fixation of unstable hangman’s fractures with discoligamentous instability or combined fractures: clinical article. J Neurosurg Spine 2013;19:569–75. [3] Zhang YS, Zhang JX, Yang QG, Shen CL, Li W, Yin ZS. Surgical management of the fractures of axis body: indications and surgical strategy. Eur Spine J 2014;23:1633–40. [4] Benzel EC, Hart BL, Ball PA, Baldwin NG, Orrison WW, Espinosa M. Fractures of the C-2 vertebral body. J Neurosurg 1994;81:206–12. [5] Levine AM, Edwards CC. The management of traumatic spondylolisthesis of the axis. J Bone Joint Surg Am 1985;67:217–26. [6] Effendi B, Roy D, Cornish B, Dussault RG, Laurin CA. Fractures of the ring of the axis. A classification based on the analysis of 131 cases. J Bone Joint Surg Br 1981;63-B:319–27. [7] Menon KV, Taif S. Detailed description of anatomy of the fracture line in hangman’s injury: a retrospective observational study on motor vehicle accident victims. Br J Radiol 2016;89:20150847. [8] Koller H, Acosta F, Tauber M, Komarek E, Fox M, Moursy M, et al. C2-fractures: Part I. Quantitative morphology of the C2 vertebra is a prerequisite for the radiographic assessment of posttraumatic C2-alignment and the investigation of clinical outcomes. Eur Spine J 2009;18:978–91. [9] Wang S, Wang Q, Yang H, Kang J, Wang G, Song Y. A novel technique for unstable Hangman’s fracture: lag screw-rod (LSR) technique. Eur Spine J 2017;26:1284–90. [10] ElMiligui Y, Koptan W, Emran I. Transpedicular screw fixation for type II Hangman’s fracture: a motion preserving procedure. Eur Spine J 2010;19:1299–305.

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