The anatomical suitability of the C1-2 complex for transarticular screw fixation

Blunt Traumatic Vertebral Artery Injury After Cervical Fracture Dislocation: A Systematic Review of the Literature

Certain high-energy blunt forces may produce unstable cervical fractures with or without dislocation. In rare cases where the superior facets are dislocated, however showing a significant increase within the last decade, these types of injuries may include vertebral artery entrapment at the involvement level leading to artery dissection or occlusion. This phenomenon is usually seen at the C4-C5 and C5-C6 levels of injury. A systematic review of the literature was performed by examining online databases such as PubMed - NCBI, Web of Science, Cochrane Library, Scopus, and Embase to identify relevant scientific articles. Keywords (MeSH terms) used in the search included cervical spine injuries, cervical spine dislocation, cerebrovascular injury, vertebral artery injury, vertebral artery injury management, and incidence of vertebral artery injury. Initially, 1516 studies were identified as a primary search for screening. After excluding papers that did not fulfill the inclusion criteria, 34 studies were included in this review. Vertebral artery injury consists of a severe complication that could compromise a surgical intervention since the patient's clinical image may be unrevealing at first. Early diagnosis and correct timing constitute the golden standard for adequate treatment. This systematic review aims to summarize the current evidence for the diagnosis, management, and treatment of blunt traumatic vertebral artery injuries.

Surgical Anatomy of Vertebral Artery in Relation to Atlantoaxial Instrumentation: A Cadaveric Study

BACKGROUND

With the advent of pedicle screws and advanced instrumentation techniques, internal fixation and stabilization of upper cervical vertebrae are possible in fractures of an axis. However, the proximity of vertebral arteries (VAs) poses a unique challenge to surgeons during these procedures and can result in profound physical impairment to patients. Cadaveric studies contributing to fine anatomical details necessitate conducting such studies.

METHODS

After receiving due ethical permission, this descriptive cross-sectional study was carried out on 10 cadavers in the department of Anatomy, All India Institute of Medical Science (AIIMS) Rishikesh. Twenty VAs were dissected along their course, and measurements of parameters related to the axis and atlas vertebra were noted.

RESULTS

The length of the pre-osseous segment related to the axis (VAX-1) on the right and left sides were from 3.8 to 14.5 mm (7.48±3.88 mm) and 4.46 to 10.5mm (6.94±2.01mm) respectively. The length of the osseous segment related to the axis (VAX-2) on the right side and left sides were from 6.82 to 31 mm (17.9±7.84mm) and 7.35 to 20 mm (15.6±4.53). The osseous segment of the VA related to the axis (VAX-2) shows genu (bend), which extends to a variable distance towards the midline. The mean distance of VA genu from the midline of the axis vertebral body on the right and left sides was 15.6mm and 17.5 mm, respectively. The percentage of superior articular facet (SAF) surface area of the axis occupied by the VA was 25-50% in nine and 50-75% in 11 cadavers, reflecting incomplete occupancy.

CONCLUSION

The study suggests that for instrumentation of the axis vertebra in the midline, the minimum distance between the genu of both sides of VA segments, related to an osseous segment of the axis (VAX-2) and medial extent of the VA groove of the atlas, should be considered as a safe zone to minimize inadvertent VA injury. During atlantoaxial fixation through a posterior approach in interarticular, pars, and pedicle screws, the surgical anatomy of the VA in relation to the osseous segment of the VA within the transverse process of the axis should be kept in mind to avoid inadvertent VA injury.

Management of the Vertebral Artery in Craniovertebral Junction Stabilization Surgery

The vertebral artery (VA) has an intimate relationship with the bones of the craniovertebral junction. An exact understanding of the VA anatomy in general and in the specific surgical case in particular is absolutely necessary in order to avoid intraoperative vascular injury. The course of the VA on the inferior aspect of the superior facet of the C2 vertebra makes it susceptible to damage during transarticular and interarticular fixation with the screw insertion in the adjacent lateral mass. The consequences of the intraoperative VA injury will depend on the patency of other arteries supplying the brain. In case of this complication, quick decision-making is essential to avoid excessive blood loss and to preserve adequate cerebral blood flow.

Biomechanical Study on Three Screw-Based Atlantoaxial Fixation Techniques: A Finite Element Study

STUDY DESIGN

This is a finite element study.

PURPOSE

This study is aimed to compare the biomechanical behaviors of three screw-based atlantoaxial fixation techniques.

OVERVIEW OF LITERATURE

Screw-based constructs that are widely used to stabilize the atlantoaxial joint come with their own challenges in surgery. Clinical and in vitro studies have compared the effectiveness of screw-based constructs in joint fixation. Nevertheless, there is limited information regarding the biomechanical behavior of these constructs, such as the stresses and strains they experience.

METHODS

A finite element model of the upper cervical spine was developed. A type II dens fracture was induced in the intact model to produce the injured model. The following three constructs were simulated on the intact and injured models: transarticular screw (C1- C2TA), lateral mass screw in C1 and pedicle screw in C2 (C1LM1-C2PD), and lateral mass screw in C1 and translaminar screw in C2 (C1LM1-C2TL).

RESULTS

In the intact model, flexion-extension range of motion (ROM) was reduced by up to 99% with C11-C2TA and 98% with C1LM1-C2PD and C1LM1-C2TL. The lateral bending ROM in the intact model was reduced by 100%, 95%, and 75% with C11-C2TA, C1LM1-C2PD, and C1LM1-C2TL, respectively. The axial rotation ROM in the intact model was reduced by 99%, 98%, and 99% with C11-C2TA, C1LM1-C2PD, and C1LM1-C2TL, respectively. The largest maximum von Mises stress was predicted for C1LM1-C2TL (332 MPa) followed by C1LM1-C2PD (307 MPa) and C11-C2TA (133 MPa). Maximum stress was predicted to be at the lateral mass screw head of the C1LM1-C2TL construct.

CONCLUSIONS

Our model indicates that the biomechanical stability of the atlantoaxial joint in lateral bending with translaminar screws is not as reliable as that with transarticular and pedicle screws. Translaminar screws experience large stresses that may lead to failure of the construct before the required bony fusion occurs.

C2 Screw fixation techniques in atlantoaxial instability: A technical review

Atlantoaxial instability (AAI) is surgically a complex entity due to its proximity to vital neurovascular structures. C1-C2 fusion has been an established standard in its treatment for a considerable time now. Here, we have outlined the most common techniques for C2 screw fixation in practice at present such as C2 pedicle, C2 pars, C2 translaminar, C2 subfacetal, C2-C3 transfacetal, and C2 inferior facet screw. We have discussed in detail the technical as well as biomechanical aspects of each technique of C2 screw fixation in AAI and explored the intricacies of each technique.

Endoscopic endonasal odontoidectomy: a long-term follow-up results for a cohort of 21 patients

BACKGROUND

Endoscopic endonasal odontoidectomy (EEO) has been described as a potential approach for craniovertebral junction (CVJ) disease which could cause anterior bulbomedullary compression and encroaching. Due to the atlantoaxial junction's uniqueness and complex biomechanics, treating CVJ pathologies uncovers the challenge of preventing C1-C2 instability. A large series of patients treated with endonasal odontoidectomy is reported, analyzing the feasibility and necessity of whether or not to perform posterior stabilization. Furthermore, the focus is on the long-term follow-up, especially those whom only underwent partial C1 arch preservation without posterior fixation.

METHODS

This study is a retrospective analysis of patients with ventral spinal cord compression for non-reducible CVJ malformation, consecutively treated with EEO from July 2011 to March 2019. Postoperative dynamic X-ray and CT scans were obtained in each case in order to document CVJ decompression as well as to exclude instability. The anterior atlas-dens interval, posterior atlas-dens interval and C1-C2 total lateral overhang were measured as a morphological criteria to determine upper cervical spine stability.

RESULTS

Twenty-one patients (11:10 F:M) with a mean age of 60.6 years old at the time of surgery (range 34-84 years) encountered the inclusion criteria. For all 21 patients, a successful decompression was achieved at the first surgery. In 11 patients, the partial C1 arch integrity did not require a posterior cervical instrumentation on the bases of postoperative and constant follow-up radiological examination. In 13 cases, an improvement of motor function was recorded at the time of discharge. Only one patient had further motor function improvement at follow-up. Among the patients that did not show any significant motor change at discharge, 4 patients showed an improvement at the last follow-up.

CONCLUSIONS

The outcomes, even in C1 arch preservation without posterior fixation, are promising, and it could be said that the endonasal route potentially represents a valid option to treat lesions above the nasopalatine line.

Pediatric craniocervical fusion: predictors of surgical outcomes, risk of recurrence, and re-operation

PURPOSE

Craniocervical junction abnormalities include a wide variety of disorders and can be classified into congenital or acquired. This study aimed to review the surgical outcome of pediatric patients who underwent craniocervical and/or atlantoaxial fusion.

METHODS

This is a retrospective cohort study including all pediatric patients (≤ 18 years) who underwent craniocervical and/or atlantoaxial fusion between 2009 and 2019 at quaternary medical city.

RESULTS

A total of 25 patients met our criteria and were included in the study. The mean age was 9 years (range: 1-17 years). There was a slight female preponderance (N = 13; 52%). Most patients (N = 16; 64%) had non-trauamatic/chronic causes of craniocervical instability. Most patients presented with neck pain and/or stiffness (N = 14; 56%). Successful fusion of the craniocervical junction was achieved in most patients (N = 21; 84%). Intraoperative complications were encountered in 12% (N = 3) of the patients. Early postoperative complications were observed in five patients (20%). Five patients (20%) experienced long-term complications. Revision was needed in two patients (8%). Older age was significantly associated with higher fusion success rates (p = 0.003). The need for revision surgery rates was significantly higher among younger age group (3.75 ± 2, p = 0.01).

CONCLUSIONS

The study demonstrates the surgical outcome of craniocervical and/or atlantoaxial fusion in pediatric patients. Successful fusion of the craniocervical junction was achieved in most patients. Significant association was found between older age and successful fusion, and between younger age and need for revision surgery.

The association between atlantoaxial instability and anomalies of vertebral artery and axis

BACKGROUND CONTEXT

A screw-rod system is the most widely used technique for atlantoaxial instability (AAI). However, neglecting anomalies of the vertebral artery and axis could lead to fatal complications. Whether or not the presence of AAI is associated with a more complicated anatomy for instrumentation is unclear.

PURPOSE

To analyze the association between AAI and anomalies of the vertebral artery and axis in patients with and without AAI.

STUDY DESIGN

A retrospective comparative study.

PATIENT SAMPLE

One hundred and twenty patients who underwent preoperative 3-dimensional computed tomography with vertebral angiography of the cervical spine at our institution from 2012 to 2020.

OUTCOME MEASURES

The C2 isthmus height, internal height of the C2 lateral mass, and C2 pedicle width were radiologically assessed.

METHODS

A case control study with matched cohort analysis was conducted. One hundred and twenty patients were divided into 2 groups according to presence of AAI, and the presence of high-riding vertebral artery (HRVA) and a narrow pedicle for insertion of the C2 pedicle screw was assessed, as was the prevalence of extraosseous vertebral artery anomaly.

RESULTS

The C2 isthmus height, C2 internal height, and C2 pedicle width were significantly narrower in the AAI group (p<.01, <.01, and <.01, respectively). A significantly greater proportion of patients with AAI had HRVA and a narrow pedicle than those without (p<.01 and < 0.01, respectively). Among patients with AAI, the C2 internal height was significantly narrower in patients with rheumatoid arthritis (p<.01). Five patients (8.3%) with AAI had vertebral artery anomaly (3 fenestration, 2 persistent first intersegmental artery), while there were no vertebral artery anomalies in patients without AAI (p<.01).

CONCLUSIONS

Vertebral artery anomalies are more common in patients with AAI. Furthermore, posterior instrumentation in patients with AAI has a narrower safe zone compared to that in patients without AAI, which may be caused by a long-lasting deformity rather than a congenital deformity. Therefore, more thorough preoperative evaluation of the anatomy should be performed in these patients.

C2/3 Transfacetal fixation: An underutilized technique of C2 fixation in the management of atlantoaxial dislocation − A technical note with review of literature

Background:

Technical Advantage:

Conclusion:

Determining C2 Pedicle Screw Placement Feasibility in the Pediatric Population: A Computed Tomographic Safe Zone Analysis

BACKGROUND

Due to high rates of anatomic variability of the C2 pedicle, thin-sliced pedicular-oriented computed tomography (CT) and 3-dimensional reconstructive CT technologies have been introduced to predict safe C2 pedicle screw placement. However, this technology may not be readily available in all centers. The purpose of this study was to perform a C2 pedicle safe zone analysis using standard sagittal CT scans to predict the feasibility of C2 pedicle screw placement in a pediatric population and to compare the results with our previously obtained safe zone analysis from the adult population.

METHODS

A retrospective analysis was performed at a single level I trauma center of pediatric patients who completed CT scans of the cervical spine. The feasibility of C2 pedicle screw placement was analyzed using our previously described C2 pedicle safe zone analysis technique. The risk profiles were compared with our previously obtained safe zone analysis from the adult population.

RESULTS

Thirty-nine consecutive patients with a mean age of 7.8±4.4 years and 78 total pedicles were included in the study. Fourteen pedicles (18%) were considered low risk, 37 (47%) were moderate risk, and 27 (35%) were high risk for vertebral artery injury. Individual patients were found to have a significant amount of side-to-side variability between pedicles with 21 patients (54%) having left and right pedicles with different risk profiles. Four patients (10%) demonstrated low risk profiles in bilateral pedicles. There was no significant difference between the risk profiles of pediatric and adult patients.

CONCLUSIONS

There is a considerable amount of anatomic variability within the pediatric C2 pedicles. Using this simple and accessible technique during the review of preoperative imaging, C2 pedicle screw placement may be considered in appropriately selected pediatric patients.

LEVEL OF EVIDENCE

Level III.

The Feasibility of C1-C2 Screw-rod Fixation in the Children 5 Years of Age and Younger

BACKGROUND

Atlantoaxial fixation is technically challenging in younger children. The C1-C2 screw-rod fixation technique is established for adults but limited data about the clinical and radiographical outcome for the treatment of children with 5 years of age or younger is available.

METHODS

All files of children who were consecutively treated for spinal disorders were reviewed. Inclusion criteria for further evaluation were: 0 to 5 years of age at initial procedure; detailed surgical report of a posterior C1-C2 fusion with mass lateral and pedicle screw-rod fixation as described by Harms; a minimum clinical and radiographical follow-up of 24 months. The postoperative and last follow-up computed tomography scan and radiographs were used to assess the positioning and stability of the C1-C2 screw-rod construct.

RESULTS

Eleven patients (3 boys) with a mean age of 46 months (range: 8 to 66 mo) fulfilled inclusion criteria and were evaluated retrospectively. The mean clinical and radiographical follow-up was 79 months (range: 24 mo to 170 mo). The diagnosis was atlantoaxial rotatory dislocation (4 cases), C1-C2 instability with subluxation (3 cases), atlantoaxial dislocation and os odontoideum (1 case), type II odontoid fracture (1 case), traumatic odontoid epiphysiolysis (1 case), and traumatic rupture of the transverse ligament with C1 subluxation (1 case). Intraoperatively and postoperatively no new neurovascular or vascular complication occurred. C1 lateral mass screws were placed correctly in all cases. Twenty-two C2 pedicle screws were placed correctly (85.7%), and 3 screws showed penetration of the pedicle wall (14.3%). No implant revision, implant failure, and pseudarthrosis were noted. Loss of correction was noted in 1 patient with unilateral C1-C2 fixation and a repeated dorsal fusion procedures were performed. A repeat procedure for implant removal and segmental release was performed in 3 patients to increase the axial rotation of the head.

CONCLUSIONS

The C1-C2 screw-rod fixation is a safe technique that achieves solid fixation of the atlantoaxial complex in young children with various disorders. The technique preserves the joint and allows for segmental release via implant removal.

Atlanto-axial rotary instability (Fielding type 1): characteristic clinical and radiological findings, and treatment outcomes following alignment, fusion, and stabilization

Atlanto-axial instability (AAI) is common in the connective tissue disorders, such as rheumatoid arthritis, and increasingly recognized in the heritable disorders of Stickler, Loeys-Dietz, Marfan, Morquio, and Ehlers-Danlos (EDS) syndromes, where it typically presents as a rotary subluxation due to incompetence of the alar ligament. This retrospective, IRB-approved study examines 20 subjects with Fielding type 1 rotary subluxation, characterized by anterior subluxation of the facet on one side, with a normal atlanto-dental interval. Subjects diagnosed with a heritable connective tissue disorder, and AAI had failed non-operative treatment and presented with severe headache, neck pain, and characteristic neurological findings. Subjects underwent a modified Goel-Harms posterior C1-C2 screw fixation and fusion without complication. At 15 months, two subjects underwent reoperation following a fall (one) and occipito-atlantal instability (one). Patients reported improvement in the frequency or severity of neck pain (P < 0.001), numbness in the hands and lower extremities (P = 0.001), headaches, pre-syncope, and lightheadedness (all P < 0.01), vertigo and arm weakness (both P = 0.01), and syncope, nausea, joint pain, and exercise tolerance (all P < 0.05). The diagnosis of Fielding type 1 AAI requires directed investigation with dynamic imaging. Alignment and stabilization is associated with improvement of pain, syncopal and near-syncopal episodes, sensorimotor function, and exercise tolerance.

Classifying vertebral artery anatomy abnormality in children with skeletal dysplasia

PURPOSE

Skeletal dysplasia (SKD) have predictably abnormal occipitocervical skeletal anatomy, but a similar understanding of their vertebral artery anatomy is not known. Knowledge and classification of vertebral artery anatomy in SKD patients is important for safe surgical planning. We aimed to determine if predictably abnormal vertebral artery anatomy exists in pediatric SKD.

METHODS

We performed a retrospective review of CTAs of the neck for pediatric patients at a single institution from 2006 to 2018. CTAs in SKD and controls were reviewed independently in blinded fashion by two radiologists who classified dominance, vessel curvature at C2, direction at C3, and presence of fenestration and intersegmental artery.

RESULTS

14 skeletal dysplasia patients were compared to 32 controls. The path of the vertebral artery at C2 foramen was no different between the cohorts or by side, right (p = 0.43) or left (p = 0.13), nor for medial or lateral exiting direction from C3 foramen on right (p = 0.82) or left (p = 0.60). Dominance was most commonly neutral in both groups (71% in SKD and 63% in controls). There were no fenestrated nor first intersegmental arteries in our cohort.

CONCLUSION

No systematic differences were detected between SKD and control patients with respect to vertebral artery anatomy. Nonetheless, surgically relevant variability was observed in both groups. Paying particular attention to the direction of exit at C3 and curvature at C2 with respect to the foramen and vessel dominance are important and easily classifiable abnormalities that both surgeons and radiologists can use to communicate and employ in pre-operative planning.

LEVEL OF EVIDENCE

III.

Intraoperative image guidance for cervical spine surgery

Intraoperative image-guidance in spinal surgery has been influenced by various technological developments in imaging science since the early 1990s. The technology has evolved from simple fluoroscopic-based guidance to state-of-art intraoperative computed tomography (iCT)-based navigation systems. Although the intraoperative navigation is more commonly used in thoracolumbar spine surgery, this newer imaging platform has rapidly gained popularity in cervical approaches. The purpose of this manuscript is to address the applications of advanced image-guidance in cervical spine surgery and to describe the use of intraoperative neuro-navigation in surgical planning and execution. In this review, we aim to cover the following surgical techniques: anterior cervical approaches, atlanto-axial fixation, subaxial instrumentation, percutaneous interfacet cage implantation as well as minimally invasive posterior cervical foraminotomy (PCF) and unilateral laminotomy for bilateral decompression. The currently available data suggested that the use of 3D navigation significantly reduces the screw malposition, operative time, mean blood loss, radiation exposure, and complication rates in comparison to the conventional fluoroscopic-guidance. With the advancements in technology and surgical techniques, 3D navigation has potential to replace conventional fluoroscopy completely.

Pediatric Spine Trauma: A Brief Review

Pediatric spinal trauma is a broad topic with nuances specific to each anatomic region of the spinal column. The purpose of this report is to provide a brief review highlighting the most important and common clinical issues regarding the diagnosis and management of pediatric spine trauma. Detailed descriptions of imaging findings along with specific operative and nonoperative management of each fracture and dislocation type are beyond the scope of this review.

Risk of the high-riding variant of vertebral arteries at C2 is increased over twofold in rheumatoid arthritis: a meta-analysis

Rheumatoid arthritis (RA) might lead to atlantoaxial instability requiring transpedicular or transarticular fusion. High-riding vertebral artery (HRVA) puts patients at risk of injuring the vessel. RA is hypothesized to increase a risk of HRVA. However, to date, no relative risk (RR) has been calculated in order to quantitatively determine a true impact of RA as its risk factor. To the best of our knowledge, this is the first attempt to do so. All major databases were scanned for cohort studies combining words "rheumatoid arthritis" and "high-riding vertebral artery" or synonyms. RA patients were qualified into the exposed group (group A), whereas non-RA subjects into the unexposed group (group B). Risk of bias was explored by means of Newcastle-Ottawa Scale. MOOSE checklist was followed to ensure correct structure. Fixed-effects model (inverse variance) was employed. Four studies with a total of 308 subjects were included in meta-analysis. One hundred twenty-five subjects were in group A; 183 subjects were in group B. Mean age in group A was 62,1 years, whereas in group B 59,9 years. The highest risk of bias regarded "comparability" domain, whereas the lowest pertained to "selection" domain. The mean relative risk of HRVA in group A (RA) as compared with group B (non-RA) was as follows: RR = 2,11 (95% CI 1,47-3,05), I² = 15,19%, Cochrane Q = 3,54 with overall estimate significance of p < 0,001. Rheumatoid arthritis is associated with over twofold risk of developing HRVA, and therefore, vertebral arteries should be meticulously examined preoperatively before performing craniocervical fusion in every RA patient.

Modified C1 lateral mass screw insertion using a threaded K-wire. A technical note

Instrumented fixation of the C1-C2 motion segment is a standard surgical technique to stabilise that spinal segment. Instability at C1-C2 can arise from a number of conditions. Fixation of the C1 lateral mass usually involves dissection and exposure of the C2 nerve root and the posterior wall of the C2 lateral mass which can result in significant bleeding from the venous plexus. Whilst image guidance is increasing in accessibility, there are few public hospitals in Australia that have access to this technology. The authors describe their technique for insertion of a C1 lateral mass screw over a threaded K-wire to avoid extensive dissection of the C2 nerve root, reducing the risk of significant haemorrhage from the epidural venous plexus during the procedure. A retrospective analysis was undertaken on 18 consecutive patients who underwent C1-C2 instrumented fixation using this technique. Indications for C1-C2 instrumented fixation included traumatic injury (10 patients), failure of non-operative management of odontoid fractures (5 patients), pathological fractures of C2 (2 patients) and inflammatory conditions (1 patient). All patients underwent successful C1-C2 stabilisation using this technique. Blood loss did not exceed 400mls in any patient. There were no vertebral artery injuries and no patient experienced a neurological deterioration. The authors propose that their technique for insertion of a C1 lateral mass screw over a threaded K-wire is safe and effective with a low risk of neurological or vertebral artery injury. The technique may be considered as a slight modification of the Harm's procedure to reduce disturbance of the adjacent venous plexus and thereby reduction in intraoperative bleeding and operative time.

[Minimally invasive techniques for traumatic injuries of the cervical spine]

Nowadays, although minimally invasive procedures are the standard for the treatment of thoracolumbar spinal injuries, these techniques are not yet established for the cervical spine. This is due to anatomical and technical reasons and also due to the fact that the classical anterior decompression and fusion procedure already fulfils the criteria of minimally invasiveness and is suitable for the vast majority of injuries. The existing literature consists mainly of case reports and small comparative cohort studies, the results of which are presented. There is a minimally invasive variant for nearly all open procedures, mainly in the upper cervical spine but also in the lower cervical spine. The further development of these promising techniques is still pending.

Minimally invasive posterior percutaneous transarticular C1-C2 screws: how I do it

BACKGROUND

Transarticular C1-C2 screw fixation, first described by Magerl, is a widely accepted used technique for C1-C2 instability with a good biomechanical stability and fusion rate.

METHOD

We present a 69-year-old woman, who was diagnosed with a C2 Odontoid fracture type III and primarily treated with conservative treatment and collar. During first 2 weeks of follow-up, the patient developed cervical pain associated with C1-C2 instability. A minimally invasive posterior C1-C2 transarticular screw instrumentation with a percutaneus approach was performed.

RESULTS AND CONCLUSION

Minimally invasive approach with tubular transmuscular approach for C1-C2 transarticular screws instrumentation is safe and effective for C1-C2 instability.

Guideline for Posterior Atlantoaxial Internal Fixation Assisted by Orthopaedic Surgical Robot

Atlantoaxial transarticular facet screw fixation (Magerl technique) and C₁ lateral mass screws combined with C₂ pedicle screws fixation (Harms technique) are the most commonly used techniques for posterior internal fixation in the upper cervical spine. Upper cervical spinal surgery is a technically demanding and challenging procedure because of complicated anatomical structures and frequent occurrence of anomalies. Accurate insertion of screws allows for stable and secure internal fixation, which is necessary for both techniques. Traditional methods under fluoroscopic assistance in this region cannot meet the requirements of high levels of accuracy and security during the procedure. Robot-assisted spinal surgery can provide accurate and reliable guidance during the screw insertion, which is evidenced in the literature. As a recently developed technique, robot-assisted surgery is supposed to be performed by skilled surgeons who have received standard training for robotic surgery. The standardized upper cervical spinal surgery assisted by the robot system needs to be introduced to these surgeons. Based on the consensus of consultant specialists, the literature review, and our local experience, this guideline included the introduction of the robotic system, the workflow of robot-assisted procedures, and the precautions to take during procedures. This guideline aims to provide a standardization of the robotic surgery for posterior atlantoaxial internal fixation.

Imaging in Spine Surgery: Current Concepts and Future Directions

OBJECTIVE

To review and highlight the historical and recent advances of imaging in spine surgery and to discuss current applications and future directions.

METHODS

A PubMed review of the current literature was performed on all relevant articles that examined historical and recent imaging techniques used in spine surgery. Studies were examined for their thoroughness in description of various modalities and applications in current and future management.

RESULTS

We reviewed 97 articles that discussed past, present, and future applications for imaging in spine surgery. Although most historical approaches relied heavily upon basic radiography, more recent advances have begun to expand upon advanced modalities, including the integration of more sophisticated equipment and artificial intelligence.

CONCLUSIONS

Since the days of conventional radiography, various modalities have emerged and become integral components of the spinal surgeon's diagnostic armamentarium. As such, it behooves the practitioner to remain informed on the current trends and potential developments in spinal imaging, as rapid adoption and interpretation of new techniques may make significant differences in patient management and outcomes. Future directions will likely become increasingly sophisticated as the implementation of machine learning, and artificial intelligence has become more commonplace in clinical practice.

Odontoid Fractures: A Critical Review of Current Management and Future Directions

Odontoid fractures represent one of the most common and controversial injury types affecting the cervical spine, being associated with a high incidence of nonunion, morbidity, and mortality. These complications are especially common and important in elderly patients, for which ideal treatment options are still under debate. Stable fractures in young patients maybe treated conservatively, with immobilization. Although halo-vest has been widely used for their conservative management, studies have shown high rates of complications in the elderly, and therefore current evidence suggests that the conservative management of these fractures should be carried out with a hard cervical collar or cervicothoracic orthosis. Elderly patients with stable fractures have been reported to have better clinical results with surgical treatment. For these and for all patients with unstable fractures, several surgical techniques have been proposed. Anterior odontoid fixation can be used in reducible fractures with ideal fracture patterns, with older patients requiring fixation with 2 screws. In other cases, C1-C2 posterior fixation maybe needed with the best surgical option depending on the reducibility of the fracture and vertebral artery anatomy. In this paper, current evidence on the management of odontoid fractures is discussed, and an algorithm for treatment is proposed.

Occipitocervical or C1-C2 fusion using allograft bone in pediatric patients with Down syndrome 8 years of age or younger

Sufficient internal fixation for occipitocervical (OC) or C1-C2 instability in pediatric patients with Down syndrome is difficult owing to small osseous structures, congenital deformities, and immature ossification. The purpose of this study was to evaluate the clinical outcomes of patients aged 8 years or younger with Down syndrome who underwent OC or C1-C2 fusion using freeze-dried allograft as bone graft substitute. The participants included seven consecutive patients aged 8 years or younger with Down syndrome who were treated for upper cervical disorders with posterior OC or C1-C2 fusion using freeze-dried allografts at our hospital between 2007 and 2016 and had a minimum follow-up of 1 year. Postoperative flexion/extension cervical radiography and computed tomography were repeated at 3 months after surgery before removal of the collar. The modified McCormick scale was used to grade functional status. The seven patients had an age range of 5-8 years (mean: 5.9 years). The mean follow-up period was 36 months (12-120 months). Six patients had os odontoideum and one had basilar invagination. Three patients underwent C1-C2 fusion, and in all cases, bilateral C1 lateral mass screws and bilateral C2 pedicle screws were used. Four patients underwent OC fusion, and in three of these cases, occipital and bilateral pedicle screws were used. One patient underwent reoperation because of occipital screw back-out with autograft; therefore, C2 lamina screws were added to pedicle screws. Solid bony fusion was achieved, and stable constructs were maintained on radiography in all patients, without infection or implant failure. In this study, we used freeze-dried allograft as a bone graft substitute, and we were able to detect bony trabeculae at the graft-recipient interface on lateral cervical radiographs and on reconstructed sagittal computed tomographic images in all patients. These results suggest that use of allograft is effective for treatment of upper cervical spine abnormalities in pediatric patients with Down syndrome.

Accuracy and Safety in Screw Placement in the High Cervical Spine: Retrospective Analysis of O-arm-based Navigation-assisted C1 Lateral Mass and C2 Pedicle Screws

STUDY DESIGN

This study was a retrospective analysis.

OBJECTIVE

The purpose of present study was to evaluate accuracy, efficiency, and safety of intraoperative O-arm-based navigation system for the placement of C1 lateral mass screw (C1LMS) and C2 pedicle screws (C2PSs) in high cervical spine operations.

SUMMARY OF BACKGROUND DATA

High screw misplacement rates, various pedicle morphometry and vertebral body size variations have led to a search of image-guided systems to improve the surgical accuracy of screw insertion in high cervical spine. The use of O-arm has been proposed for more accurate and efficient spinal instrumentation.

MATERIALS AND METHODS

Between June 2009 and August 2016, a total of 48 patients with atlantoaxial instability were surgically treated using the image-guidance system. To reconstruct atlantoaxial instability, we have been using Harm's technique of C1LMS and C2PS fixations. A frameless, stereotactic O-arm-based image-guidance system was used for correct screw placement. Postoperative computed tomographic scan with multiplanar reconstructions were used to determine the accuracy of the screw placement.

RESULTS

A total of 182 screws, including 90 C1LMS and 92 C2PSs were inserted using image-guidance system. In total, 4.4% (4/90) of C1LMS and 7.6% (10/92) of C2PS had cortex violation over 2 mm and considered as "significant." Among the significant cortex violations, "unexpected breech" was 3.3% of all the screws inserted. Two (2.1%) screws inserted had perforated the vertebral artery canal and iatrogenic vertebral artery stenosis was proved with postoperative computed tomography angiography. When divided into time periods, 60% of significant breech occurred during the beginning stage, 40% during adaptation stage and none during expert stage.

CONCLUSIONS

In this study, the authors demonstrated that use of image-guidance system seems to be beneficial for high cervical instrumentation which requires much experience and steep learning curves. However, incidence of cortex violation does not disappear completely due to the close proximity to spinal canal and surrounding vessels.

Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical analysis

OBJECTIVEC1-2 is a highly mobile complex that presents unique surgical challenges to achieving biomechanical rigidity and fusion. Posterior wiring methods have been largely replaced with segmental constructs using the C1 lateral mass, C1 pedicle, C2 pars, and C2 pedicle. Modifications to reduce surgical morbidity led to the development of C2 laminar screws. The C1 posterior arch has been utilized mostly as a salvage technique, but recent data indicate that this method provides significant rigidity in flexion-extension and axial rotation. The authors performed biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct, collected morphometric data from a population of 150 CT scans, and performed a feasibility study of a freehand C1 PAS technique in 45 cadaveric specimens.METHODSCervical spine CT scans from 150 patients were analyzed to determine the average C1 posterior tubercle thickness and size of C1 posterior arches. Eight cadavers were used to compare biomechanical stability of intact specimens, C1 lateral mass/C2 pars screw, and C1 PAS/C2 pars screw constructs. Paired comparisons were made using repeated-measures ANOVA and Holm-Sidak tests. Forty-five cadaveric specimens were used to demonstrate the feasibility and safety of the C1 PAS freehand technique.RESULTSMorphometric data showed the average craniocaudal thickness of the C1 posterior tubercle was 12.3 ± 1.94 mm. Eight percent (12/150) of cases showed thin posterior tubercles or midline defects. Average posterior arch thickness was 6.1 ± 1.1 mm and right and left average posterior arch length was 28.7 mm ± 2.53 mm and 28.9 ± 2.29 mm, respectively. Biomechanical testing demonstrated C1 lateral mass/C2 pars and C1 PAS/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared with intact specimens (p < 0.05). The C1 lateral mass/C2 pars screw construct provided significant rigidity in lateral bending (p < 0.05). There was no statistically significant difference between the two constructs in flexion-extension, lateral bending, or axial rotation. Of the C1 posterior arches, 91.3% were successfully cannulated using a freehand technique with a low incidence of cortical breach (4.4%).CONCLUSIONSThis biomechanical analysis indicates equivalent stability of the C1 PAS/C2 pars screw construct compared with a traditional C1 lateral mass/C2 pars screw construct. Both provide significant rigidity in flexion-extension and axial rotation. Feasibility testing in 45 cadaveric specimens indicates a high degree of accuracy with low incidence of cortical breach. These findings are supported by a separate radiographic morphometric analysis.

Management of Combined Atlas Fracture with Type II Odontoid Fracture: A Review of 21 Cases

PURPOSE

To evaluate the therapeutic effects of combined atlas fracture with type II (C₁-type II) odontoid fractures and to outline a management strategy for it.

PATIENTS AND METHODS

Twenty three patients with C₁-type II odontoid fractures were treated according to our management strategy. Nonoperative external immobilization in the form of cervical collar and halo vest was used in 13 patients with stable atlantoaxial joint. Surgical treatment was early performed in 10 patients whose fractures with traumatic transverse atlantal ligament disruption or atlantoaxial instability. The visual analog scale (VAS), neck disability index (NDI) scale, and American Spinal Injury Association (ASIA) scale at each stage of followup were then collected and compared.

RESULTS

Compared to pretreatment, the VAS score, NDI score, and ASIA scale were improved among both groups at followup evaluation after treatment. However, in the nonsurgical group, one patient (1/11) developed nonunion which required surgical treatment in later stage and one patient (1/13) with halo vest immobilization had happened pin site infection. Two patients of the surgical group (2/11) had appeared minor complications: occipital cervical pain in one case and cerebrospinal fluid leakage in one case. Two patients (2/23) were excluded from nonsurgical treatment group because their followup period was less than 12 months. Twenty one patients were followed up regularly with an average of 23.9 months (range 15-45 months).

CONCLUSIONS

We outlined our concluding management principle for the treatment of C₁-type II odontoid fractures based on the nature of C₁ fracture and atlantoaxial stability. The treatment principle can obtain satisfactory results for the management of C₁-type II odontoid fractures.

Safety and accuracy of freehand versus navigated C2 pars or pedicle screw placement

BACKGROUND CONTEXT

C2 pedicle and pars screws require accurate placement to avoid injury to nearby neurovascular structures. Freehand, fluoroscopically guided, and computed tomography (CT)-based navigation techniques have been described in the medical literature.

PURPOSE

The present study aims to compare the safety and accuracy of the freehand technique versus stereotactic navigation for the placement of C2 pedicle and pars screws.

STUDY DESIGN/SETTING

This study was a retrospective review of consecutive patients treated with posterior fixation constructs.

PATIENT SAMPLE

A total of 220 consecutive patients were treated with posterior fixation constructs containing C2 pars or pedicle screws placed at our institution.

OUTCOME MEASURES

Computed tomography imaging was used to assess the accuracy of screw placement. Intraoperative complications and incidence of stroke or mortality within 30 days of the operation were analyzed.

METHODS

A retrospective review was conducted of consecutive patients treated with posterior fixation constructs containing C2 pars or pedicle screws placed by spine surgeons between January 1, 2010, and August 31, 2016. Clinical and radiographic data were collected and analyzed. Screw accuracy was graded independently by two reviewers according to the following criteria: grade A (no breach), grades B-E (breach with transverse foramen obstruction of 1%-25%, 26%-50%, 51%-75%, or 76%-100%, respectively), and grade M (medial breach). Screws were divided into acceptable (grades A and B) and unacceptable (grades C-E and M).

RESULTS

A total of 426 C2 pars or pedicle screws (312 freehand, 114 navigated) were placed in 220 patients (160 freehand, 60 navigated). Complications were similar between the groups: three vertebral artery injuries (two [1%] freehand, one [2%] navigated; p>.99), five deaths (four [3%] freehand, one [2%] navigated; p>.99), and one (2%) stroke in the navigated group (p=.61). Computed tomography imaging was available for accuracy grading of 182 screws (131 freehand, 51 navigated). No breaches (grade A) occurred in 113 of the freehand screws (86%) and in 34 of the navigated screws (67%) (p=.006). More screws had acceptable placement in the freehand group (123 of 131, 94%) than in the navigated group (42 of 51, 82%) (p=.02).

CONCLUSIONS

In patients with postoperative CT imaging (43%), the freehand technique was found to be more accurate than CT-based navigation for C2 pedicle or pars screw placement. Complication rates did not differ between the two techniques in this study.

Comprehensive Drilling of C1-2 Facets and Multiplanar Realignment for Atlanto-Axial Dislocation and Basilar Invagination: 2-Dimensional Operative Video

The management for congenital atlantoaxial dislocation (AAD) and basilar invagination (BI) has significantly changed in the last 2 decades. Authors operate these cases through a direct posterior approach by opening and manipulating the C1-2 joints (irrespective of C1 assimilation), modifying Goel's technique. The joints in these cases are often oblique in both sagittal and coronal planes giving rise to anteroposterior and vertical slip of C1 on C2. Asymmetry on either side gives rise to coronal/lateral angular tilt along with rotational component. The authors have described comprehensive drilling of the facets (osteotomies) in sagittal and coronal planes to release the joints. Metallic spacers with graft window packed with bone chips are inserted to compensate for the drilled bone. Screws are inserted in C1 lateral mass and C2 pedicle. A rod is fastened between the screw heads and further multiplanar realignment can be achieved by manipulating the rod. The technique obviates the need for transoral decompression and the C1-2 joints are closely fused. The facetal osteotomies coupled with manipulation for realignment in all planes provides a composite solution for even the extremely complex lateral dislocation or complete spondyloptosis with severely deformed C1-2 joints that may be difficult with techniques described earlier. There is no need to include occipital squama and multiple cervical vertebrae in the construct, irrespective of the C1 assimilation. The authors have operated over 200 cases of irreducible CAAD/BI with good outcome and have illustrated their technique in this video. Proper informed consent was obtained from the patient.

Biomechanical evaluation of C1 lateral mass and C2 translaminar bicortical screws in atlantoaxial fixation: an in vitro human cadaveric study

BACKGROUND CONTEXT

Atlantoaxial fixation with C1 lateral mass-C2 translaminar bicortical (C1LM-C2TB) screws has been reported to afford good stability with the least risk of injury to vertebral artery. However, no comparative in vitro studies have been conducted to evaluate the biomechanical stability of this method.

PURPOSE

This study aimed to compare in vitro biomechanics of fixation with C1LM-C2TB with fixation with C1 lateral mass-C2 translaminar unicortical screws (C1LM-C2TU) and with C1 lateral mass-C2 pedicle screws (C1LM-C2PS).

STUDY DESIGN

This is an in vitro biomechanical study.

METHODS

Fifteen fresh-frozen human cadaveric cervical spines (C1-C3) were tested after destabilization by transverse-alar-apical ligament disruption. Instrumentation was performed with three fixation constructs: C1LM-C2PS, C1LM-C2TU, and C1LM-C2TB. Flexion, extension, lateral bending, and axial rotation were tested. Range of motion and neutral zone pre-fatigue and post-fatigue values were measured.

RESULTS

No significant differences were observed in flexion-extension among the three groups. However, C1LM-C2TB fixation was superior to C1LM-C2TU fixation in lateral bending and axial rotation.

CONCLUSION

C2 translaminar bicortical screws are biomechanically superior to C2TU screws for fixation of the atlantoaxial complex, and it is equivalent to C2PS fixation. C2 translaminar bicortical screws or C2PS should be preferred over C2TU screws.

Radiologic Analysis of C2 to Predict Safe Placement of Pedicle Screws

Background

Preoperative assessment of C2 pedicle morphology is critical to safe pedicle screw placement. To avoid iatrogenic injury, complex digital templating software has been introduced; however, this technology may not be available in many centers. We report a technique for preoperative assessment of C2 pedicle screw placement safety based upon 2-dimensional sagittal computed tomography (CT) scan images and verify its utility in clinical practice.

Methods

A total of 46 consecutive patients underwent cervical spine CT scans between 2005 and 2011. The C2 pedicle morphology was assessed on sagittal CT imaging by 5 independent reviewers to determine the feasibility and risk associated with pedicle screw placement. Thirty consecutive patients underwent C2 pedicle screw placement and were followed clinically for a minimum of 2 years. The ability to place a screw was noted, and accuracy of screw placement was assessed postoperatively by CT scan.

Results

The CT scan analysis demonstrated that 11% (5/46) of patients had sufficient pedicle size bilaterally to allow safe placement of long pedicle screws with a low risk of vertebral artery injury, whereas 15% (7/46) were considered a high risk bilaterally. Screw placement was deemed low risk in 28%, moderate risk in 38%, and high risk in 34%. Excellent intraobserver reliability and good interobserver reliability was observed. Clinically, 18 of 20 (90%) low-risk and 21 of 24 (88%) moderate-risk pedicle screws were placed safely versus 5 of 16 (31%) high-risk pedicle screws (P < .001).

Conclusions

Using the described technique for evaluating the C2 pedicle via sagittal CT scan images allows for safe and reliable pedicle screw placement without relying upon complex digital templating software, which may have limited availability.

Level of Evidence

II.

Clinical Relevance

This study aids in the surgical decision-making behind the placement of C2 pedicle screws using CT scans without reliance upon complex digital templating software.

A Novel C2 Screw Trajectory: Preliminary Anatomic Feasibility and Biomechanical Comparison

BACKGROUND

Pedicle screw and translaminar screw fixation in C2 may not be applicable in many patients with anatomic abnormalities or narrow laminar thickness and spinous process height. The aim of this study was to assess morphometric and mechanical feasibilities of a novel alternative screw trajectory that pierces the bifid base of C2.

METHODS

Anatomic measurements that determined the feasibility of spinous process bifid base (SPB) screw fixation were assessed in 14 cadaveric C2 vertebrae. Pullout tests to assess ultimate fixation strength for 3 screw trajectories (transpedicular, translaminar, and SPB) were performed in cadaveric vertebrae for comparison.

RESULTS

Anatomic measurements included mean spinous process height (10.4 ± 4.2 mm) and mean bilateral bifid base length (10.1 ± 2.2 mm) and thickness (left, 4.4 ± 1.0 mm; right, 4.3 ± 0.9 mm). In 64% (9/14) of specimens, bifid base length was ≥9 mm. Mean pullout strength for transpedicle, translaminar, and SPB screws in 9 viable specimens was 648 ± 305 N, 628 ± 417 N, and 755 ± 279 N.

CONCLUSIONS

SPB screw fixation may be viable anatomically and mechanically for C2 fixation. Feasibility of SPB screw fixation is determined by length, thickness, and mutual angle of the bilateral bifid bases. Patients with thin (<4 mm) and short (<9 mm) bifid bases are not likely to be suitable candidates. SPB screw fixation shows potential as an alternative approach or a salvage technique for patients with high-riding vertebral arteries or severely thin C2 lamina and warrants further investigation.

Delayed epidural pseudoaneurysm following cervical laminectomy and instrumentation in a patient with canal stenosis secondary to skeletal fluorosis: A case report

RATIONALE

The typical intraoperative presentation of vertebral artery injury (VAI) usually involves profuse bleeding and requires immediate treatment. However, an occult VAI may occur intraoperatively and result in delayed life-threatening epidural pseudoaneurysm several days postoperatively.

PATIENT CONCERNS

A 21-year-old man with compressive cervical myelopathy resulting from canal stenosis of skeletal fluorosis underwent decompression of C1 to C7 and instrumentation from C2 to C7. No impressive bleeding event occurred during the operation. On postoperative day 40, progressive quadriplegia developed.

DIAGNOSES

Pseudoaneurysm of the VA was established by angiography.

INTERVENTIONS

After occlusion of the right VA, the patient underwent hematoma clearing.

OUTCOMES

Fortunately, the patient experienced significant recovery of neurologic function after the second surgery.

LESSONS

From this case, we realize even in the absence of obvious signs of VAI during a cervical operation, postoperative evaluation should be mandatory for suspected bleeding events occurring at VAI-prone sites during surgery. Moreover, the bone morphological abnormality of skeletal fluorosis was determined to be the most important risk contributing to VAI in this case. The safety limits of bone removal should be determined preoperatively to avoid the effects of bone morphological abnormalities.

Improving C1-C2 Complex Fusion Rates: An Alternate Approach

The surgical repair of atlantoaxial instabilities (AAI) presents complex and unique challenges, originating from abnormalities and/or trauma within the junction regions of the C1-C2 atlas-axis, to surgeons. When this region is destabilized, surgical fusion becomes of key importance in order to prevent spinal cord injury. Several techniques can be utilized to provide for the adequate fusion of the atlantoaxial construct. Nevertheless, many individuals have less than ideal rates of fusion, below 35%-40%, which also involves the C2 nerve root being sacrificed. This suboptimal and unavoidable iatrogenic complication results in the elevated probability of complications typically composed of vertebral artery injury. This review is a retrospective analysis of 87 patients from Cedars Sinai Medical Center in Los Angeles, California, who had the C1-C2 surgical fusion procedure performed within the time frame from 2001 to 2008, with a mean follow-up period of three years. These patients had presented with typical AAI symptoms of fatigability, limited mobility, and clumsiness. Diagnosis of C1-C2 instability was documented via radiographic studies, typically utilizing computed tomography (CT) scans or x-rays. All patients had bilateral C1 lateral masses and C2 pedicle screws. In addition, the C1-C2 joint was accessed by retracting the C2 nerve root superiorly and exposing the joint by utilizing a high-speed burr. The cavity that is developed within the joint is packed with local autologous bone from the cephalad resection of the C2 laminae. Fusion of the C1-C2 joint was achieved in all patients and a final follow-up was conducted approximately three years postoperative. Of the 87 patients, two presented with occipital headaches resulting from the C1 screws impinging on the C2 nerve root. The issue was rectified by removing instrumentation in both patients after documenting complete fusion via radiographic studies, with complete resolution of symptoms. No vertebral artery or spinal cord injuries were reported as a result of the minor complication. Overall, we aim to describe a safe and reliable alternative technique to fuse C1-C2 instability by focusing on intra-articular arthrodesis complementing instrumentation fixation. This methodology is advantageous from a biomechanical standpoint secondary to axial loading, as well as the large surface area available for arthrodesis. Additionally, this technique does not involve the resection of the C2 nerve root, resulting in low risk for vertebral artery or spinal cord injury.

When does intraoperative 3D-imaging play a role in transpedicular C2 screw placement?

INTRODUCTION

The stabilization of an atlantoaxial (C1-C2) instability is demanding due to a complex atlantoaxial anatomy with proximity to the spinal cord, a variable run of the vertebral artery (VA) and narrow C2 pedicles. We perfomed the Goel & Harms fusion in combination with an intraoperative 3D imaging to ensure correct screw placement in the C2 pedicle. We hypothesized, that narrow C2 pedicles lead to a higher malposition rate of screws by perforation of the pedicle wall. The purpose of this study was to describe a certain pedicle size, under which the perforation rate rises.

PATIENTS AND METHODS

In this retrospective study, all patients (n=30) were operated in the Goel & Harms technique. The isthmus height and pedicle diameter of C2 were measured. The achieved screw position in C2 was evaluated according to Gertzbein & Robbin classification (GRGr).

RESULTS

A statistically significant correlation was found between the pedicles size (isthmus height/pedicle diameter) and the achieved GRGr for the right (p=0.002/p=0.03) and left side (p=0.018/p=0.008). The ROC analysis yielded a Cut Off value for the pedicle size to distinguish between an intact or perforated pedicle wall (GRGr 1 or ≥2). The Cut-Off value was identified for the isthmus height (right 6.1mm, left 5.4mm) and for the pedicle diameter (6.6mm both sides).

CONCLUSION

The hypothesis, that narrow pedicles lead to a higher perforation rate of the pedicle wall, can be accepted. Pedicles of <6.6mm turned out to be a risk factor for a perforation of the pedicle wall (GRGr 2 or higher). Intraoperative 3D imaging is a feasible tool to confirm optimal screw position, which becomes even more important in cases with thin pedicles. The rising risk of VA injury in these cases support the additional use of navigation.

Biomechanical study of novel unilateral C1 posterior arch screws and C2 laminar screws combined with an ipsilateral crossed C1-C2 pedicle screw-rod fixation for atlantoaxial instability

INTRODUCTION

Current surgical methods to treat atlantoaxial instability pose potential risks to the surrounding blood vessels and nerves of operative approach. Therefore, more secure and highly effective methods are expected. This study sought to assess the biomechanical efficacy of a novel unilateral double screw-rod fixation system by comparing with traditional and emerging fixation methods in cadaveric models.

MATERIALS AND METHODS

Ligamentous cervical spines (C0-C7) from ten fresh cadaveric specimens were used to complete range of motion (ROM) test in their intact condition (control group), destabilization, and stabilization after different fixations, including unilateral C1-C2 pedicle screws (PS) with a screw-rod system (Group A), bilateral C1-C2 PS with screw-rod systems (Group B), unilateral C1 posterior arch screws (PAS) and C2 laminar screws (LS) combined with an ipsilateral paralleled C1-C2 PS-rod (Group C), and unilateral C1 PAS and C2 LS combined with an ipsilateral crossed C1-C2 PS-rod (Group D). After that, pullout strength test was performed between PS and PAS using ten isolated atlas vertebras.

RESULTS

All fixation groups reduced flexibility in all directions compared with both control group and destabilization group. Furthermore, comparisons among different fixation groups showed that bilateral C1-C2 PS-rod (Group B), unilateral C1 PAS + C2 LS combined with an ipsilateral paralleled C1-C2 PS-rod (Group C) and unilateral C1 PAS + C2 LS combined with an ipsilateral crossed C1-C2 PS-rod (Group D) could provide a better stability, respectively, in all directions than unilateral C1-C2 PS-rod (Group A). However, no statistical significance was observed among Groups B, C, and D. Data from pullout strength test showed that both C1 PS (585 ± 53 N) and PAS (463 ± 49 N) could provide high fixed strength, although PS was better (P = 0.009).

CONCLUSION

The surgical technique of unilateral C1 PAS + C2 LS combined with a ipsilateral crossed C1-C2 PS-rod fixation could provide a better stability than the traditional unilateral PS-rod fixation and a same stability as bilateral PS-rod fixation, but with less risk of neurovascular injury. Therefore, this new technique may provide novel insight for an alternative of atlantoaxial instability treatment.

Aortic arch origin of the left vertebral artery: An Anatomical and Radiological Study with Significance for Avoiding Complications with Anterior Approaches to the Cervical Spine

Complications from anterior approaches to the cervical spine are uncommon with normal anatomy. However, variant anatomy might predispose one to an increased incidence of injury during such procedures. We hypothesized that left vertebral arteries that arise from the aortic arch instead of the subclavian artery might take a more medial path in their ascent making them more susceptible to iatrogenic injury. Fifty human adult cadavers were examined for left vertebral arteries having an aortic arch origin and these were dissected along their entire cervical course. Additionally, two radiological databases of CTA and arteriography procedures were retrospectively examined for cases of aberrant left vertebral artery origin from the aortic arch over a two-year period. Two cadaveric specimens (4%) were found to have a left vertebral artery arising from the aortic arch. The retrospective radiological database analysis identified 13 cases (0.87%) of left vertebral artery origin from the aortic arch. Of all cases, vertebral arteries that arose from the aortic arch were much more likely to not only have a more medial course (especially their preforaminal segment) over the cervical vertebral bodies but also to enter a transverse foramen that was more cranially located than the normal C6 entrance of the vertebral artery. Spine surgeons who approach the anterior cervical spine should be aware that an aortic origin of the left vertebral artery is likely to be closer to the midline and less protected above the C6 vertebral level. Clin. Anat. 30:811-816, 2017. © 2017Wiley Periodicals, Inc.

C1 lateral mass screw insertion caudally from C2 nerve root - An alternate method for insertion of C1 screws: A technical note and preliminary clinical results

BACKGROUND

C1 lateral mass screw was widely used for fixation of the upper cervical spine. However, massive bleeding from the C1-2 venous plexus is sometimes encountered. In this study, we proposed an alternate method for C1 lateral mass screw insertion, which involves insertion of the screws caudally from the C2 nerve root to reduce bleeding from C1-2 venous plexus.

METHODS

Seven patients with atlantoaxial lesions were included in this study. The mean age at surgery was 65.9 (34-82) years. The mean follow-up period was 23.1 (12-38) months. All patients underwent atlantoaxial fusion with C1 lateral mass screws, which were inserted caudally from the C2 nerve root. All screws were inserted using O-arm based navigation system. Operative time, blood loss, C2 nerve root injury and perioperative complications were investigated. The accuracy of C1 screws and bone union were evaluated using postoperative computed tomography.

RESULTS

A total of 13 C1 lateral mass screws were inserted using this method. The mean operative time was 224 (144-305) min. The mean blood loss was 209 (100-357) g. One perioperative complication was observed, which was recurrent laryngeal nerve palsy. There were no vertebral artery or spinal cord injuries. No case of massive bleeding from the C1-2 venous plexus was observed. One patient complained of postoperative occipital neuralgia, which disappeared in 2 weeks. No malposition of C1 lateral mass screws was observed on postoperative computed tomography. Bone union was observed in all patients.

CONCLUSION

The C1 lateral mass screw insertion caudally from the C2 nerve root may become an alternate method for insertion of C1 screws.

Top 50 most-cited articles on craniovertebral junction surgery

Background:

Craniovertebral junction is a complex anatomical location posing unique challenges to the surgical management of its pathologies. We aimed to identify the fifty most-cited articles that are dedicated to this field.

Methods:

A keyword search using the Thomson Reuters Web of Knowledge was conducted to identify articles relevant to the field of craniovertebral junction surgery. The articles were reviewed based on title, abstract, and methods, if necessary, and then ranked based on the total number of citations to identify the fifty most-cited articles. Characteristics of the articles were determined and analyzed.

Results:

The earliest top-cited article was published in 1948. When stratified by decade, 1990s was the most productive with 16 articles. The most-cited article was by Anderson and Dalonzo on a classification of odontoid fractures. By citation rate, the most-cited article was by Herms and Melcher who described Goel's technique of atlantoaxial fixation using C1 lateral mass screws and C2 pedicle screws with rod fixation. Atlantoaxial fixation was the most common topic. The United States, Barrow Neurological Institute, and VH Sonntag were the most represented country, institute, and author, respectively. The significant majority of articles were designed as case series providing level IV evidence.

Conclusion:

Using citation analysis, we have provided a list of the most-cited articles representing important contributions of various authors from many institutions across the world to the field of craniovertebral junction surgery.

Prevalence of High-Riding Vertebral Artery and Morphometry of C2 Pedicles Using a Novel Computed Tomography Reconstruction Technique

Study Design

Cross-sectional, matched-pair comparative study.

Purpose

To determine whether a thin-sliced pedicular-oriented computed tomography (TPCT) scan reconstructed from an existing conventional computed tomography (CCT) scan is more accurate for identifying vertebral artery groove (VAG) anomalies than CCT.

Overview of Literature

Posterior atlantoaxial transarticular screw fixation and C2 pedicle screws can cause vertebral artery (VA) injury. Two anatomic variations of VAG anomalies are associated with VA injury: a high-riding VA (HRVA) and a narrow pedicle of the C2 vertebra. CCT scan is a reliable method used to evaluate VAG anomalies; however, its accuracy level remains debatable. Literature comparing the prevalence of C2 VAG anomalies between CCT and TPCT is limited.

Methods

A total of 200 computed tomography scans of the upper cervical spine obtained between January 2008 and December 2011 were evaluated for C2 VAG anomalies (HRVA and narrow pedicular width) using CCT and TPCT. The prevalence of C2 VAG anomalies was compared using these two different measurement methods via a McNemar's test.

Results

Of the 200 patients studied, 23 HRVA (6.01%; 95% confidence interval [CI], 3.61%–8.39%) were detected with CCT, whereas 66 HRVA (16.54%; 95% CI, 12.85%–20.23%) were detected with TPCT (p<0.001). Sixty-two narrow pedicles (15.58%; 95% CI, 11.99%–19.15%) were detected with CCT, whereas 90 narrow pedicles (22.83%; 95% CI, 18.58%–26.87%) were detected with TPCT (p<0.001).

Conclusions

VAG anomalies are commonly observed. A preoperative evaluation using TPCT reconstructed from an existing CCT revealed a significantly higher prevalence of C2 VAG anomalies than did CCT and showed comparable prevalence to previously published studies using more sophisticated and higher risk techniques. Therefore, we propose TPCT as an alternative preoperative evaluation for C2 screw placement and trajectory planning.

Understanding the Course of Vertebral Artery at Craniovertebral Junction in Occipital Assimilation of Atlas: Made Simplified Using Conventional Angiography

Introduction Preoperative assessment of vertebral artery (VA) is important to avoid its injury during surgery at craniovertebral junction (CVJ). The main concern is the course of third segment of VA (V3) while performing instrumentation at CVJ, that is, segment of VA from its course through transverse foramen of C2 to its course along the posterior arch of C1. This segment of VA includes its passage through C1 transverse foramen as well. This observational study was done to analyze the course, curvature, and termination of VA in patients with occipital assimilation of atlas at CVJ, a complex congenital anomaly, and compared with the normal course for better understanding especially by young neurosurgeons and spine surgeons. Materials and Method This is an observational study that included patients with occipitalized C1 with or without associated anomalies. Out of 30 patients of CVJ anomalies, 16 patients had occipitalized atlas. Digital subtraction angiography was done in all cases. It was done by selectively catheterizing the VA using standard Seldinger's technique and both anteroposterior and lateral projections were taken. Results The course of VA was not identical on either side in any individual. It was lengthened and tortuous in all patients. Different types of anomalous course were encountered like bypassing transverse foramen of C1, close relation with C1-2 facet joints, variable course along the posterior arch of C1, abnormal termination and fenestration of VA. Conclusion Craniovertebral junction anomalies are not only bony or neural, but are vascular too. Complex CVJ anomalies are associated with higher incidence of anomalous course of the VA, an important surgical consideration.

A novel method of C1-C2 transarticular screw insertion for symptomatic atlantoaxial instability using a customized guiding block: A case report and a technical note

Atlantoaxial instability treated with the C1-2 transarticular screw fixation is biomechanically more stable; however, the technique demanding and the potential risk of neurovascular injury create difficulties for clinical usage, and there is still lack of clinical experience till now.We reported an adult female patient with symptomatic atlantoaxial instability due to rheumatoid arthritis that was successfully treated with a bilateral C1-C2 transarticular screw fixation using a customized guiding block. We preoperatively determined the trajectories for bilateral C1-C2 transarticular screws on a 3-dimensional reconstruction model from the computed tomography (CT) and self-developed computer software, and designed a rapid prototyping customized guiding block in order to offer a guide for the entry point and insertion angle of the C1-C2 transarticular screws.The clinical outcome was good, and the follow-up period was >3 years. The accuracy of the screws is good in comparison with preoperative and postoperative CT findings, and no neurovascular injury occurred.The patient was accurately and successfully treated with a bilateral C1-C2 transarticular screw fixation using a customized guiding block.

Neurological outcomes following iatrogenic vascular injury during posterior atlanto-axial instrumentation

BACKGROUND

Iatrogenic vascular injury is a feared complication of posterior atlanto-axial instrumentation. A better understanding of clinical outcome and management options following this injury will allow surgeons to better care for these patients. The object of the study was to systematically review the neurologic outcomes after iatrogenic vascular injury during atlanto-axial posterior instrumentation.

METHODS

We performed a systematic review of the Medline database following PRISMA guidelines. In our analysis, we included any retrospective cohort studies, prospective cohort studies, case reports, cases series, or systematic reviews with patients who had undergone posterior atlanto-axial fusion via screw rod constructs (SRC) or transarticular screws (TAS) that reported a patient with an injury to an arterial vessel directly attributable to the surgical procedure.

RESULTS

Sixty cases of vascular injury were reported in 2078 (2.9%) patients over 27 publications. The average age for this patient population was 55.7+/-17.9. Vascular injury following posterior C1/2 instrumentation resulted in ipsilateral stroke in 10.0% (n=6/60) and non-persistent neurologic deficit in 6.7% (n=4/60) of cases with the deficit being permanent (not including death) in 1.7% (n=1/60) of cases. Four patients (6.7%) died. Arteriovenous fistula or pseudoaneurysm occurred in 8.3% (n=5/60) and 3.3% (n=2/60) of cases, respectively. Eight patients (13.3%) underwent endovascular repair of the injury with no permanent deficit.

CONCLUSION

Neurological morbidity after iatrogenic vascular injury during posterior C1/2 fixation is higher than previously reported in literature. Some patients may benefit from endovascular treatment. Surgeons should be aware of normal and anomalous vertebral artery anatomy to avoid this potentially catastrophic complication.

Surgical Intervention for Instability of the Craniovertebral Junction

Surgical approaches for stabilizing the craniovertebral junction (CVJ) are classified as either anterior or posterior approaches. Among the anterior approaches, the established method is anterior odontoid screw fixation. Posterior approaches are classified as either atlanto-axial fixation or occipito-cervical (O-C) fixation. Spinal instrumentation using anchor screws and rods has become a popular method for posterior cervical fixation. Because this method achieves greater stability and higher success rates for fusion without the risk of sublaminar wiring, it has become a substitute for previous methods that used bone grafting and wiring. Several types of anchor screws are available, including C1/2 transarticular, C1 lateral mass, C2 pedicle, and translaminar screws. Appropriate anchor screws should be selected according to characteristics such as technical feasibility, safety, and strength. With these stronger anchor screws, shorter fixation has become possible. The present review discusses the current status of surgical interventions for stabilizing the CVJ.

Short isthmic versus long trans-isthmic C2 screw: anatomical and biomechanical evaluation

INTRODUCTION

The Harms technique is now considered as the gold standard to stabilize C1-C2 cervical spine. It has been reported to decrease the risk of vertebral artery injury. However, the risk of vascular injury does not totally disappear, particularly due to the proximity of the trans-isthmic C2 screw with the foramen transversarium of C2. In order to decrease this risk of vertebral artery injury, it has been proposed to use a shorter screw which stops before the foramen transversarium.

OBJECT

The main objective was to compare the pull-out strength of long trans-isthmic screw (LS) versus short isthmic screw (SS) C2 screw. An additional morphological study was also performed.

METHOD

Thirteen fresh-frozen human cadaveric cervical spines were included in the study. Orientation, width and height of the isthmus of C2 were measured on CT scan. Then, 3.5-mm titanium screws were inserted in C2 isthmus according to the Harms technique. Each specimen received a LS and a SS. The side and the order of placement were determined with a randomization table. Pull-out strengths and stiffness were evaluated with a testing machine, and paired samples were compared using Wilcoxon signed-rank test and also the Kaplan-Meier method.

RESULTS

The mean isthmus transversal orientation was 20° ± 6°. The mean width of C2 isthmus was less than 3.5 mm in 35 % of the cases. The mean pull-out strength for LS was 340 ± 85 versus 213 ± 104 N for SS (p = 0.004). The mean stiffness for the LS was 144 ± 40 and 97 ± 54 N/mm for the SS (p = 0.02).

DISCUSSION

The pull-out strength of trans-isthmic C2 screws was significantly higher (60 % additional pull-out resistance) than SSs. Although associated with an inferior resistance, SSs may be used in case of narrow isthmus which contraindicates 3.5-mm screw insertion but does not represent the first option for C2 instrumentation.

LEVEL OF EVIDENCE

Level V.