AO Spine Clinical Practice Recommendations for the Management of Subaxial Spine Fractures

Abstract

Study design

Literature Review with clinical recommendations.

Objective

To highlight impactful studies on subaxial cervical fractures, identified by the AO Spine Knowledge Forum Trauma and Infection group, with recommendations for their integration into clinical practice.

Methods

Four studies on subaxial cervical fractures that have the potential to shape current practice in subaxial cervical fractures were selected and reviewed. Each study was chosen for its contribution to a critical phase in subaxial fractures management: diagnosis and imaging, surgical vs conservative treatment, and selection of approach.

Results

Four studies were highlighted. Article 1: Rutsch et al evaluated the sensitivity and specificity of CT, MRI, plain radiography, and LODOX-Statscan in identifying cervical spine injuries. We strongly recommend the use of CT/MRI as gold standard for radiological workup in cervical spine injuries. Article 2: Cirillo et al performed a systematic review of predictor of failure to conservative treatment for isolated unilateral facet fractures. We conditionally recommend surgical treatment in floating lateral mass and greater fragment size. Article 3: Singh et al evaluated the predictors of failure after stand-alone ACDF in subaxial fractures. We conditionally recommend adding posterior fusion in PLL injury, bilateral facet joint dislocation and age above 60 years. Article 4: Kwon et al prospectively randomized and compared anterior vs posterior approach in unilateral facet joint injury. We conditionally recommend anterior surgical fixation in unilateral facet injuries without spinal cord injury.

Conclusion

This article provides spine surgeons with evidence-based recommendations to enhance standardization and effectiveness of the management of subaxial spine fractures.

Introduction

Cervical spine injuries occur in 2.4% of trauma cases and approximately half of all traumatic injuries to the cervical spine involve the subaxial spine which extends from C3 to C7. ¹ These injuries can cause deformity, subluxation and dislocation, resulting in neurological damage. ² Despite the evolution of classification systems to standardize communication and guide treatment decisions, there is still a lack of consensus on the treatment and best approach for different patterns of subaxial fractures. Currently, there are some challenging questions facing spine surgeons when treating subaxial fractures (SF), such as optimal imaging studies, fracture patterns requiring surgical treatment, and selection of the surgical approach.

To address these questions, the AO Spine Knowledge Forum Trauma and Infection group has reviewed 4 impactful studies, critically reviewing them for clinical relevance and scientific merit, summarized the most relevant clinical information and provided recommendations to help busy clinicians integrate current evidence into their practice.

Diagnostic: Imaging for C-Spine Fractures

Article 1: Cervical Spine Trauma – Evaluating the Diagnostic Power of CT, MRI, X-Ray and LODOX3

Niklas Rutsch, Pascale Amrein, Aristomenis K. Exadaktylos, Lorin M. Benneker, Florian Schmaranzer, Martin Müller, Christoph E. Albers, Sebastian F. Bigdon. Injury. 2023 Jul;54(7):110771.

Clinical Rationale

Appropriate treatment of SF is contingent upon timely injury recognition. While the Canadian C-Spine rule (CCR) ⁴ and National Emergency X-Radiography Utilization Study (NEXUS) guide clinical decision making, ⁵ there is little consensus regarding the optimal imaging modality and what imaging studies are necessary. The reported sensitivity of plain radiographs to detect subaxial injuries in the literature ranges from 44% to 93%.^6,7 Meanwhile, the sensitivity of CT has been reported to be as high as 100% in some studies, which, however, is not always matched by clinical experience.^8,9 To evaluate the diagnostic utility of different imaging modalities, Rutsch et al conducted a retrospective cohort study comparing the sensitivity and specificity of CT, MRI, plain radiography, and LODOX (Low Dosage 2D X-ray technology) in identifying cervical spine injuries in blunt trauma patients presenting with neck pain requiring a radiographic evaluation according to the NEXUS criteria. ³

Clinical Summary

This retrospective single-center study included adult blunt trauma patients with neck pain presenting to a large level one trauma center and tertiary referral hospital over a 5-year period who required radiographic evaluation in accordance with the NEXUS criteria. Pediatric patients and those with incomplete medical records were excluded. Patient demographics, mechanism of injury, radiographic modalities (CT, MRI, plain radiographs, and LODOX) and radiological findings, injury type as well as clinical management were recorded. A full case review by a senior spine surgeon served as the “gold standard” by which the true/false positives and true/false negatives of each imaging modality were assessed. Sensitivity and specificity of each imaging modality were calculated.

4996 patients were identified of which 2321 patients (1700 patients with low-energy mechanism, 73.2%; 621 patients with high energy trauma, 26.8%) met the NEXUS criteria for further radiographic evaluation. Based on a full case review by a junior researcher and spine surgeon, 2135 patients were classified as uninjured and 186 as injured.

Of the 2321 included patients, 2120 had CT scans (injuries identified in 178 patients), 206 had MRI (injuries identified in 78 patients), 215 had plain radiographs (injuries identified in 22 patients), and 498 had LODOX (injuries identified in 3 patients). When compared to the full case review, CT demonstrated 88.6% sensitivity and 99% specificity with sensitivity increased to 89.8% with orthopedic surgeon consultation. MRI demonstrated a sensitivity of 88.5% and specificity of 96.9%. MRI identified cervical injury in 14 patients with false negative CT scans with 8 subsequently treated conservatively (neurologically intact) and 6 patients ultimately underwent surgery (5 with neurologic deficits).

Plain radiography had a sensitivity of 36.4% and specificity of 95.1% and LODOX demonstrated a sensitivity of 5.3% and specificity of 100%.

Methodological Review

This single-center retrospective cohort study aimed to evaluate the sensitivity and specificity of CT, MRI, plain radiography, and LODOX in identifying cervical spine injuries in blunt trauma patients. The inclusion criteria were well-defined, and the methodology is clearly described. Strengths of the study include the large sample size and the evaluation of imaging modality specificity and sensitivity in “real-world” practice in the acute setting. The notable limitations of this study given its retrospective nature are the lack of a direct comparison of the relative performance of different imaging modalities in the same patients and long-term follow-up for missed or mis-diagnosed injuries.

Recommendation for Integrating into Your Clinical Practice

Based on the presented data, we conditionally recommend against the use of plain radiography as the sole modality to rule out suspected traumatic cervical injury in patients meeting the NEXUS criteria. We strongly recommend the use of CT/MRI as the gold standard for radiological workup in cervical spine injuries. Further, we conditionally recommend the use of MRI in patients with neurologic deficits with normal CT scans.

Conservative vs Operative Decision Pathway: Management for Non-Displaced Facet Fractures

Article 2: Risk Factors for Failure of Non-Operative Management in Isolated Unilateral Non-Displaced Facet Fractures of the Subaxial Cervical Spine: Systematic Review and Meta-Analysis ¹⁰

Ignacio Cirillo, Guillermo Alejandro Ricciardi, Juan Pablo Cabrera, Felipe Lopez Muñoz, Lyanne Romero Valverde, Andrei Joaquim, Charles Carazzo, and Ratko Yurac. Global Spine J. 2025 May;15(4):2467-2479.

Clinical Rationale

Traumatic subaxial facet injuries encompass a broad spectrum from unilateral nondisplaced fractures to bilateral facet fractures with joint dislocations and possible neurological compromise.

The management of unilateral nondisplaced or minimally displaced facet joint injuries is a subject of debate, especially in neurologically intact patients. ¹¹ Most of these injuries are considered mechanically stable and treated nonoperatively, however, some of these injuries do fail with nonoperative treatment and require surgical management after all. ¹² The identification of factors associated with failure of nonoperative management in these isolated unilateral facet fractures could prevent treatment failure in these patients.

Clinical Summary

This systematic review aimed to identify risk factors for failure of nonoperative treatment of isolated subaxial facet fractures in neurologically intact patients. The authors initially identified 1639 studies and finally included 8 studies.

The review included 2 studies that considered fracture subtype as a risk factor for unsuccessful non-operative management, specifically distinguishing floating lateral mass fractures from other simpler subtypes.^13,14 Both studies employed a similar definition of unsuccessful non-operative management, defined as a translation of more than 3.5 mm of the vertebral body. In this regard, lateral floating mass fractures were found to have 5.4 times higher odds of failure of nonoperative management (OR = 5.4 95% CI = 1.32-22.19). Additionally, a decrease in absolute cervical facet fracture height (measured in cm) was found to be correlated with successful conservative treatment in 2 studies from this review.^15,16 As described by Spector et al ¹⁵ Facets height are measured in para sagittal CT images, total vertical height of the facet’s articular surface (from superior to inferior) is divided by the vertical height of the fracture fragment.

Methodological Review

This systematic review was conducted in accordance to the PRISMA statement. Studies included were selected according to the following criteria: Adult patients with isolated superior or inferior facet joint fractures treated conservatively (rigid collar, soft collar, halo vest). Studies involving participants with fracture dislocations, osteoporosis or metabolic diseases, low-energy trauma, pathological fractures, rheumatoid arthritis, ankylosing spondylitis, or diffuse idiopathic skeletal hyperostosis (DISH) were excluded.

The primary outcome was failure of non-operative management, defined by the presence of pseudarthrosis, posterior translation, new neurological symptoms or persistent pain. Risk of Bias of the included studies was evaluated using the ROBINS-I tool for non-randomized exposure studies. Additionally, the data was evaluated for its suitability for quantitative meta-analysis, and the GRADE approach was employed to assess the certainty of the evidence. ¹⁷ The main limitation of this systematic review is related to the level of certainty of the studies included, rated as “very low” by the GRADE quality analysis.

Recommendation for Integrating into Your Clinical Practice

Based on the evidence provided by this study, we conditionally recommend surgical treatment in patients with a floating lateral mass also known as F3 according to the AO Spine Subaxial Injury Classification system. ¹⁸ Additionally, we conditionally recommend primary surgical treatment in patients with greater fracture fragment size (measured either in absolute terms or as a percentage) corresponding with F2 pattern from AO Spine Subaxial Injury Classification, since these characteristics are associated with failure of non-operative treatment.

Surgical Decision: When is 360° Fusion Needed?

Article 3: Predictors of Failure After Primary Anterior Cervical Discectomy and Fusion for Subaxial Traumatic Spine Injuries ¹⁹

Aman Singh, Victor Gabriel El-Hajj, Alexander Fletcher-Sandersjöö, Nabeel Aziz, Abdul Karim Ghaith, Charles Tatter, Simon Blixt, Gunnar Nilsson, Mohamad Bydon, Paul Gerdhem, Erik Edström & Adrian Elmi-Terander. Eur Spine J 33, 2332-2339 (2024)

Clinical Rationale

Despite the development of the AO Spine subaxial cervical spine injury classification system (AOSpine SCICS), ¹⁸ the Subaxial Cervical AO Spine Injury Score ¹⁸ and a few studies proposing an approach algorithm such as the one described by Dvorak et al, ²⁰ to date, no universally accepted treatment guideline exists and therefore decision-making for the best treatment strategy for traumatic subaxial fractures is mainly based on surgeon’s preference and experience.^21,22

Widely accepted treatment options include anterior only procedures (mainly ACDF), posterior stabilization or combined anteroposterior (360°) techniques. ²³ Some studies have shown favor towards the anterior approach in terms of patient satisfaction and surgical site infection incidence compared to posterior techniques but a robust recommendation for one or the other option for the treatment of subaxial fractures is currently still lacking in international literature.^24,25,26 Anteroposterior approaches however have been shown to carry more risks in terms of early mortality and surgical site infections due to the naturally greater extensiveness of the surgical approach.^26,27 With this, the question as of when to add posterior fixation to an anterior fixation technique in the treatment of subaxial fractures remains. To answer this question, Singh et al conducted a retrospective single-center study identifying risk factors for treatment failure in ACDF and for the subsequent need of additional posterior fixation in patients with traumatic subaxial fractures. ¹⁹

Clinical Summary

In this study, adult patients who sustained traumatic SF and who were treated with single- or multilevel ACDF were included. In total, 341 patients with complete clinical and radiological data (trauma CT and MRI) were reviewed.

A standard right-sided Smith-Robinson approach was performed for all cases by one or more senior neurosurgeons. In all cases, PEEK (polyetheretherketone) cages and an anterior plate stabilized with bicortical screws were used. The authors defined construct failure as one of the following: instrumentation failure, implant subsidence, loss of alignment, screw loosening or combinations of these resulting in radiological instability. Supplementary posterior fixation was used with lateral mass screws usually 2 levels above and below the fracture. In case of extension to the upper thoracic levels, pedicle screws were used.

All patients underwent postoperative neurological examination within the first 24 h. Low-dose CT-scans were performed within 24 h of surgery, as well as 4 and 12 weeks after surgery. In case of additional posterior fixation, the mentioned radiological follow-up protocol was repeated.

The most frequently encountered trauma mechanism was motor vehicle accidents (32%) followed by falls from height (29%). In most of the cases (87%) the anterior longitudinal ligament was injured. Almost one third (28%) presented preoperatively with ASIA grade D, followed by C (16%) and B (5.3%) as well as A (5.3%) whereas the rest of the collective (45%) were neurologically intact prior to surgery.

The median time from presentation to index surgery was 2.0 days. The majority (78%) underwent single-level ACDF, whereas 16% underwent 2-level and 6.2% underwent ≥3-level ACDF.

A delayed posterior fixation as an addendum to the ACDF was performed in 11 cases (3.2%) within a median of 20 days after index surgery, In all cases PF was performed due to construct failure with radiological signs of instability. The univariable regression model identified the following predictors for additional posterior fixation: age (OR = 1.06, P = .017), height (OR = 0.92, P = .031), PLL injury (OR = 9.78, P = .004), ligamentum flavum injury (OR = 7.00, P = .005), bilateral facet joint dislocation (OR = 12.0, P < .001), and traumatic spondylolisthesis (OR = 10.3, P = .003).

Multivariate logistic regression identified PLL injury (OR = 5.61, P = .048), bilateral facet joint dislocation (OR = 6.54, P = .010) and age, especially above the age of 60 years, (OR = 1.07, P = .015) as independent predictors of ACDF failure and therefore the need for additional posterior fixation.

Methodological Review

This single-center retrospective cohort study aimed to determine independent risk factors for failure of ACDF and subsequently the need for additional posterior fixation. The inclusion (traumatic subaxial injury, treated with single- or multilevel ACDF at index surgery) and exclusion (ankylosing spondylitis, non-traumatic cases, traumatic cases primarily treated with posterior or anteroposterior surgery, traumatic cases treated with ACCF and cases with incomplete records) criteria were well-defined, and the authors used sound statistical methods. Strengths of the study are the large-sample size, the rigorous initial radiological assessment and the relatively long radiological follow-up. Limitations of the study comprise the lack of health-related quality of life patient-reported outcome measures. Further, the retrospective nature of this study at a single institution doesn’t allow the application of the presented findings to a general population and therefore a multi-center prospective study is needed to confirm these findings.

Recommendation for Integrating into Your Clinical Practice

Based on the presented data, we conditionally recommend considering an additional posterior fixation or only posterior approach at index surgery in patients aged above 60 years of age, patients with PLL injury as well as patients with bilateral facet joint dislocation.

Surgical Decision - Approach to the C-Spine

Article 4: A prospective Randomized Controlled Trial of Anterior Compared With Posterior Stabilization for Unilateral Facet Injuries of the Cervical Spine ²⁸

Kwon BK, Fisher CG, Boyd MC, Cobb J, Jebson H, Noonan V, Wing P, Dvorak MF. A prospective randomized controlled trial of anterior compared with posterior stabilization for unilateral facet injuries of the cervical spine. J Neurosurg Spine. 2007 Jul;7(1):1-12. doi: 10.3171/SPI-07/07/001.

Clinical Rationale

Cervical unilateral facet injuries present with a vast spectrum of injury patterns from undisplaced fractures, floating lateral masses, and subluxation to dislocation. ²⁹ The AOSpine subaxial cervical spine injury classification system was developed to guide and standardize treatment. ¹⁸ However, debate persists regarding the choice of the best approach when a patient is deemed for surgical intervention. There is a lack of consensus with significant treatment variations worldwide. ²⁹ The literature provides inconclusive results making a clear choice of approach by the spine surgeon difficult. ³⁰

Surgical management is often favoured in the context of unilateral facet fractures when displaced. But unilateral facet fractures often do not meet conventional criteria for instability.^31,32 Ultimately, between 21% and 80% of these fractures will ultimately fail nonoperative management and require surgical intervention.^15,33 Posterior surgical fixation and anterior fixation have both shown advantages and disadvantages.^34–36 Few studies to date have provided a clear answer regarding the superiority of one approach. To address this knowledge gap, Kwon et al conducted a prospective randomized controlled trial comparing anterior and posterior fixation. ²⁸

Clinical Summary

In this study, adult patients selected for surgical treatment by the treating surgeon with unilateral facet injury from C3 to T1 were included. Enrolled patients were randomized between anterior and posterior surgical approach according to block randomization procedure. Patients were excluded if there was an associated spinal cord injury, other injuries or conditions affecting mobilization or cognition, signification compression fracture of the adjacent vertebral body as well as disc herniation on MR imaging.

Twenty patients were randomized to anterior procedure and twenty-two patients were randomized to posterior procedure. Ten patients presented with radiculopathy with 6 randomized to anterior treatment and 4 to posterior surgery. Thirty-four patients had fracture subluxations. Eight patients had purely ligamentous injuries without fracture.

Anterior approach consisted of an anterior cervical discectomy and fusion with iliac crest autograft and locking plate. Posterior approach consisted of lateral mass screw-plate fixation and/or interspinous/oblique wiring as well as harvesting of iliac crest graft for fusion. At the time of the study, there was no clear superiority for the different posterior stabilization techniques. All patients received self-controlled analgesia, mobilization with orthoses and standard regimens provided by physiotherapists and occupational therapists.

The primary outcome was the duration of postoperative time required for the patient to meet all discharge criteria. The median time to discharge was 2.75 days in the anterior group and 3.5 days in the posterior group (P = .096). Four patients in the posterior group had wound infection requiring a longer stay. There was no infection in the anterior group.

Several secondary outcomes were evaluated. The early postoperative mean pain score (VAS for neck pain) was slightly lower in the anterior group, but this did not reach statistical significance (P = .15). There were no statistical differences between the groups for the patient reported outcomes at 12 months follow-up (SF-36, NASS cervical, and neurological scores). Eleven patients in the anterior group reported difficulty swallowing or changes in their voice at the time of discharge. All patients experienced resolution of the symptoms by the 3-month follow-up. No major complication occurred.

The anterior group had a fusion rate of 100% at the radiographic 1-year follow-up. The posterior group had a fusion rate of 89% with 2 patients suffering pseudoarthrosis. The difference was not statistically significant however (P = .49). The posterior group had a mean sagittal alignment of 1.6 degrees of kyphosis compared to 8.8 degrees of lordosis in the anterior group, which was statistically different (P = .0001).

Methodological Review

This randomized controlled trial compared anterior vs posterior surgery for unilateral facet fracture in patients who were deemed surgical by their treating surgeon. The primary outcome was postoperative time to meet discharge criteria. There was ultimately no difference in terms of the primary outcome. However, some notable differences were observed in the secondary outcomes.

This study is a well-designed RCT providing level 1 evidence. However, the sample size is small, and the non-significant primary outcome may lead to imprecision, which may be a cause for downgrade. Randomization was described, but allocation concealment and blinding were not possible as it is the case for most surgical trials. Additionally, the power and sample size calculations were not described. Therefore, the final GRADE rating would be moderate-quality evidence.

Recommendation for Integrating into Your Clinical Practice

Based on this study, we conditionally recommend anterior surgical fixation in unilateral cervical facet injuries without spinal cord injury when appropriate. This conditional recommendation is based on the trend towards less pain in the anterior group, the lower rate of infections which affected the length of stay for the posterior group as well as the higher rate of fusion and better sagittal alignment. This recommendation is conditional given that the study was not powered for the findings in the secondary outcomes.

Furthermore, anterior approach should be used with caution in certain patient populations such as the elderly. Additionally, anterior fusion alone in the presence of subjacent vertebral endplate fracture may lead to higher rates of failure, as previously reported by Johnson et al. ³⁷ Therefore, posterior or combined fixation in the presence of a subjacent endplate fracture may be preferred.

Limitations

This review article has some limitations that should be acknowledged. First, there is a potential selection bias in the included articles, as the selection process was based on the authors’ expertise, the subject matter, and the quality of the evidence. Despite this limitation, we believe that our selection reflects the most relevant gaps in the literature regarding the diagnosis and management of subaxial cervical spine trauma. Finally, we did not address additional research questions that may be of interest, such as surgical approach preferences across different injury patterns or postoperative management strategies. These topics require further investigation and are beyond the scope of the present review.

Conclusion

Despite the current gaps in the literature in the management of subaxial cervical fractures, we have identified some articles that can provide some insights into diagnosis, conservative and surgical decision making and selection of approach. Rutsch et al ³ evaluated the sensitivity and specificity of CT, MRI, plain radiography, and LODOX in identifying cervical spine injuries, this retrospective single center study with supported the use of CT/MRI as gold standard for radiological workup in cervical spine injuries due to the high sensitivity and specificity compared with x-rays. In the study of Cirillo et al, ¹⁰ the systematic review found that floating lateral mass and cervical facet fracture height were predictors of failure to conservative treatment. Regarding Singh et al ¹⁹ study, the authors evaluated predictors of failure after stand-alone ACDF in subaxial cervical fractures, the need posterior fusion was found in cases with PLL injury, bilateral facet joint dislocation and age above 60 years. Finally, Kwon et al ²⁸ in a prospective randomized study, authors supported anterior surgical fixation in unilateral cervical facet injuries without spinal cord injury.

Conditional recommendations were given in most studies due to the level of evidence found. Prospective, multicenter studies are required to refine these recommendations necessary to universally dictate applicable guidelines. While these studies provide valuable insights, clinicians must apply them with an awareness of their limitations.