Anatomic relationship of the internal carotid artery to the C1 vertebra: A case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas

Strategies to avoid internal carotid artery injury in “sandwich” atlantoaxial dislocation patients during surgery

PURPOSE

To elucidate the anatomic relationship between the internal carotid artery (ICA) and the bony structures of the craniovertebral junction among "sandwich" atlantoaxial dislocation (AAD) patients, and to analyze the risks of injury during surgical procedures.

METHODS

The distance from the medial wall of ICA to the midsagittal plane (D1), the shortest distance between the ICA wall and the anterior cortex of the lateral mass of atlas (LMA) (D2) on the most caudal and cranial levels of LMA and the angle (A) between the sagittal plane passing through the screw entry point of C1 lateral mass(C1LM) screw and the medial tangent line of the vessel passing through the entry point were measured. Besides, the location of ICA in front of the atlantoaxial vertebra was divided into 4 categories (Z1-Z4).

RESULTS

There was a statistically difference between the male and female patients regarding D1, and the difference between D2 at level a and level b as well as angle A between the left and right sides were statistically different (p < 0.05). Ninety-two ICAs (57.5%) were anteriorly located in Z3, 50 (31.3%) were located in Z4, 17 were located in Z2, and only one ICA was located in Z1 in all 80 patients.

CONCLUSIONS

In "sandwich" AAD patients, particular attention should be paid to excessively medialized ICA to avoid ICA injury during trans-oral procedures, and the risk of injuring the ICA with more cranially and medially angulated C1LM screw placement was relatively less during posterior fixation procedures. A novel classification of ICA location was used to describe the relationship between ICA and LMA.

Iatrogenic Vascular Injury Associated with Cervical Spine Surgery: A Systematic Literature Review

BACKGROUND

Iatrogenic vascular injury is an uncommon complication of anterior and/or posterior surgical approaches to the cervical spine. Although the results of this injury may be life-threatening, mortality/morbidity can be reduced by an understanding of its mechanism and proper management.

METHODS

We conducted a literature review to provide an update of this devastating complication in spine surgery. A total of 72 articles including 194 cases of vascular lesions following cervical spine surgery between 1962 and 2021 were analyzed.

RESULTS

There were 53 female and 41 male cases (in addition to 100 cases with unreported sex) with ages ranging from 3 to 86 years. The vascular injuries were classified according to the spinal procedures, such as anterior or posterior cervical spine surgery. The interval between the symptom of the vascular injury and the surgical procedure ranged from 0 to 10 years. Only two-thirds of patients underwent intra- or postoperative imaging and the most frequently injured vessel was the vertebral artery (86.60%). Laceration was the most common lesion (41.24%), followed by pseudoaneurysm (16.49%) and dissection (5.67%). Vascular repair was performed in 114 patients. The mortality rate was 7.22%, and 18.04% of patients had 1 or more other complications. Most presumed causes of vascular lesions were by instrumentation/screw placement (31.44%) or drilling (20.61%). Sixteen patients had an anomalous artery. Direct microsurgical repair was achieved in only 15 cases.

CONCLUSIONS

Despite increased anatomical knowledge and advanced imaging techniques, we need to consider the risk of vascular injury as a surgical complication in patients with cervical spine pathologies.

Lateral mass screw placement in the atlas: description of a novel surgical technique, radiographic parameters, and review of the literature

Background

Numerous techniques of C1 lateral mass screw placement have been described. We sought to delineate the radiographic angle of safety medially and laterally and describe a novel surgical technique of C1 lateral mass screw placement. We sought to (I) determine the angle of safety medially and laterally of the C1 lateral mass; (II) assess the size available of the lateral mass in the AP and coronal planes; (III) describe novel technique of insertion of a C1 lateral mass screw utilizing navigation and a novel start point.

Methods

We retrospectively reviewed cervical computed tomography (CT) images of normal adults. Radiographic measurements were then obtained using these images including the angle (degrees) of safety medially and lateral of the C1 lateral mass bilaterally, as well as the length and width (mm) of the C1 lateral masses. A novel surgical technique was used by identifying the confluence of the medial aspect of the posterior arch and the lateral mass. This confluence is then marked out as the C1 screw start point. Under navigation guidance, lateral mass screws were placed with 0 degrees of medial-lateral angulation from posterior to anterior.

Results

Forty-five patients with a mean age of 52.6±25.6 years (33% female) were included. The mean medial and lateral angle of safety of the C1 lateral mass bilaterally was 23±3.8 degrees and 32±5 degrees, respectively. Average length and width of the lateral mass was 17.7 and 13.3 mm respectively.

Conclusions

This study describes the radiographic window of safety medially and laterally for safe and reproducible placement of C1 lateral mass screws. Further, a novel technique using a medial start point and navigation guidance with 0 degrees of angulation in the coronal plane is described. Further research is required to assess outcomes of patients utilizing this method as well as biomechanical studies to assess this construct strength compared to others that are frequently used.

[Early intraoperative and postoperative complications of C1-C2 fixation using the Goel-Harms technique : How often? Which? Why?]

Fractures of the axis are among the most frequent spinal injuries. Posterior C1-C2 fixation according to Goel-Harms is an accepted alternative to the more traditional procedures: initial stability has been shown and there is a wide range of indications but there is a paucity of data on possible complications. Such knowledge, however, is essential in order to improve outcomes.Thus, the aim of the study was:1. to describe the frequency, type and severity of early postoperative complications following C1-C2 fixation according to Goel-Harms,2. to investigate whether there is a correlation between frequency and severity of complications,3. to detect risk factors for complications.Patients included in this study were treated surgically using the C1-C2 fixation according to Goel-Harms between March 2011 and July 2018. Data were taken from our hospital database and checked via OPS 10 code "S12.1". We analyzed age, sex, ASA score, blood loss, operating time and complications. These data were extracted from clinical data sheets.A total of 134 patients were detected, 54% female, mean age 75 years and mean ASA score 3. There were 122 complications. All these complications were observed in 50% of the patients. These were mainly minor complications (32%), and 18% severe complications. Mortality was 2%. We found that patients with more severe complications also had significantly more complications when compared to patients with minor complications (Fisher's exact test, p = 0.001). Preoperative ASA score was the only risk factor to significantly influence the number (p = 0.001) and severity (p = 0.002) of postoperative complications. Each increase of the preoperative ASA score increased the risk to get one more complication by a factor of 2.55 (odds ratio 2.55) and increased the risk to get a severe complication by a factor of 2.43 (odds ratio 2.43). Intraoperative blood loss, patient age and duration of surgery, however, were not identified as risk factors for complications.

Occipitocervical Fixation: General Considerations and Surgical Technique

STUDY DESIGN

Narrative literature review.

OBJECTIVE

To review and present details on the occipitocervical fixation (OCF) technique as well as considerations for planning the procedure.

METHODS

We present the surgical technique of OCF in a step-by-step didactic and practical manner with surgical tips and tricks, including C1 and C2 screw fixation techniques. Additionally, we discuss complications, the extension of fusion, types of OCF, and how to avoid common side effects associated with OCF.

RESULTS

The complex and mobile anatomy of the craniocervical junction, when requiring fixation and fusion, warrants rigid instrumentation that can be achieve using a modern screw-plate-rod construct. Indications for OCF are craniocervical instability, and atlantoaxial instability when selective atlantoaxial fusion is not feasible. OCF generally involves occiput-C2 fusion. C1 fixation is generally unnecessary, since it increases the surgical time and is associated with the risk of vascular complications. Selective occiput-C2 fusion is recommended when there is no need for including the cervical subaxial region (eg, when stenosis or fractures coexist in the subaxial spine), and good fixation is achieved at C2. Most instrumentation systems now have occipital plates that are not pre-integrated to rods, making fixation much simpler. Surgical steps, from position to wound closure, are presented in detail, with pearls for practice and discussion of cervical alignment.

CONCLUSIONS

OCF is a challenging procedure, with potential risk of severe adverse effects. Understanding the surgical indications, as well as the nuances of the surgical technique, is required to improve patient outcomes and avoid complications.

The internal carotid artery and the atlas: anatomical relationship and implications for C1 lateral mass fixation

PURPOSE

The internal carotid artery (ICA) is potentially at risk during posterior fixation of C1. In this study, we performed a CT-based anatomical analysis of the relationship between the internal carotid artery and the lateral mass of the atlas.

METHODS

We analysed 30 CT angiography of the cervical spine, and we measured on both sides the distance of the carotid artery from the midline, distance of the ICA from the anterior cortex of C1 and from the ideal C1 screw entry point. We measured the angle between the sagittal plane passing through the entry point and the tangent line of the vessel. Separated statistical analysis between left and right sides, between male and female patients, and differentiation by age were also performed.

RESULTS

Sixty ICAs were studied. The mean distance of the ICA from the midline was 23.3 ± 4.3 mm, with a minimum of 15 mm. The distance between the ICA and the anterior cortical layer of C1 was 4.8 ± 2.7 mm, with a minimum of 1.1 mm. The distance between the screw entry point and the arterial wall was 22.6 ± 2.8 mm, with a minimum of 17.5 mm. The mean angle was 10.4°, with a minimum of 11°.

CONCLUSIONS

Although rare, intraoperative lesion of the ICA is reported and the spine surgeon must be aware of this risk. Careful preoperative planning is mandatory and the position of the ICA in relation to C1 must be assessed. The anatomical parameters presented in this paper can be useful to reduce the risk of ICA injury.

Computed Tomography Scan-Based Morphometric Analysis of Lateral Masses of Atlas Vertebrae in Normal Indian Population

Study Design

A cross-sectional observational study involved the analysis of computed tomography (CT) scan data from 125 Indian subjects of 18 years or older with normal imaging findings. Scans were obtained from patients with head injuries as a part of the screening process along with brain CT scans.

Purpose

To establish the dimensions of lateral masses of the atlas vertebrae in normal disease-free Indian individuals.

Overview of Literature

Lateral mass fixation has become the standard of care in fixation of the supra-axial cervical spine. Many studies have investigated the dimensions of lateral masses in cadaveric specimens; however, studies involving the radiological morphometric analysis of the lateral masses of the atlas vertebra in living patients are lacking.

Methods

Subjects underwent craniovertebral junction CT scans during evaluations of head injury. All had normal radiology reports. The CT scans were obtained using a CT Philips Brilliance 64 machine (Philips, Amsterdam, Netherlands) with a slice thickness of 1 mm and then analyzed using Horos software ver. 2.0.2 (Horos Project, Annapolis, MD, USA) on a MacBook.

Results

Lateral masses of the atlas vertebrae were found to be larger in males than females and larger on the right than the left side. The angle of permissible medialization was found to be larger on the right side. The analysis of the average dimensions indicated the conventionally described screw positions to be safe.

Conclusions

The present study provides information that may help to establish standard dimensions of lateral masses of the atlas vertebrae among the normal Indian population. We demonstrate that there is no significant difference when compared with the Western population. The results presented here will be of use to clinicians as they may inform preoperative planning for lateral mass fixation surgeries.

Usefulness of a New Electronic Conductivity Device with a Pedicle Probe and a Multi-axis Angiography Unit for Inserting a C1 Lateral Mass Screw Safely and Tightly: A Technical Note

The C1 lateral mass screw (LMS) is widely used as one of the screws for atlantoaxial fixation. Tight bicortical screwing from the posterior to anterior cortical margin of the atlas is recommended. However, important structures, such as the internal carotid artery, are located around this area so precision is required to avoid injuring them. We describe the usefulness of a new electronic conductivity device (ECD) with a pedicle probe and a multi-axis angiography unit for inserting the C1 LMS. Four consecutive patients who were treated with C1 and C2 posterior fixation using an ECD and a multi-axis angiography unit in the hybrid operating room were included. All patients were treated successfully. Seven of eight bicortical screws could be inserted into the perfectly ideal location. The median (interquartile range) distance from the anterior margin of the atlas to the tip of the screw was 0.81 mm (0.43, 1.21 mm). This study suggested that the ECD and multi-axis angiography unit are useful for inserting the C1 LMS safely and tightly.

Posterior Inferior Cerebellar Artery Infarction Originating at C1-2 after C1-2 Fusion

Vertebral artery injuries associated with C1 lateral mass screw insertion rarely occur during C1-2 fusion. The posterior inferior cerebellar artery (PICA) is uncommonly located at the C1 lateral mass insertion position. A 71-year-old woman with atlanto-axial subluxation and cord compression underwent C1-2 fusion. Sixth nerve palsy and diplopia were detected postoperatively, and decreased consciousness occurred on postoperative day 4. Brain magnetic resonance image (MRI) and computed tomography (CT) revealed PICA infarction. In the preoperative CT angiography, the PICA originated between the C1 and C2 level. In the postoperative CT scan, the PICA was not visible. The patient was treated conservatively for two weeks and recovered. PICA originating between the C1 and C2 level comprises 1.1–1.3% of cases. Therefore, vertebral artery anomalies should be evaluated prior to C1-2 fusion to prevent vessel injuries.

Anatomical study of the ventral neurovascular structures and hypoglossal canal for the surgery of the upper cervical spine

The aim of this study is to evaluate the anatomical relationship between the bony structures and ventral neurovascular structures around craniovertebral junction (CVJ). Eleven fresh-frozen cadaveric specimens were dissected around CVJ. The anatomical relationships were evaluated between C1 bony structures (midline, lateral margin of the C1 lateral mass (LM) and C1 transverse process (TP)) and ventral neurovascular structure such as ICA and HN. Morphometric evaluation of occipital condyle was also performed. The diameter of the HN and the ICA was 2.4 ± 0.5 mm and 5.1 ± 0.2 mm. The ICA was located lateral to the C1 LM in 44.4% (ICA Group 1) and in front of lateral half of the C1 LM in 55.6% (ICA Group 2). The HN was located lateral to the C1 LM in 85% (HN Group 1) and in front of lateral half of the C1 LM in 15% (HN Group 2). HN Group 2 was significantly more common in ICA Group 2 (p < 0.05, OR = 2.00, 95% CI: 1.07-3.71). There was significant correlation between ICA and HN in terms of the distance from the midline, C1 LM and TP (r = 0.67, 0.87 and 0.76 respectively, P < 0.01). In conclusion, the HN location is related with ICA location and the medially located ICA is a risk factor of the HN located ventral to the C1 LM. These results demonstrate the vulnerability of the neurovascular structures during CVJ surgery and suggest that preoperative 3D-CTA or enhanced CT scan can be useful in guiding surgical technique.

Change of Anatomical Location of the Internal Carotid Artery Relative to the Atlas with Congenital Occipitalization and the Relevant Clinical Implications

INTRODUCTION

The occipitalization of the atlas (OA) is always associated with multiplanar dislocation and olisthy of the C1 over C2 facets, which may change the anatomical relationship between the internal carotid artery (ICA) and the atlas. The purpose of this current study is to identify the location of the ICA relative to the anterior aspect of the atlas in patients with OA and define the clinical implications for screw placement.

METHODS

We retrospectively reviewed the computed tomography angiography data of 86 patients with OA and 86 control subjects. Several parameters were also measured to quantitatively evaluate the mutual relationship.

RESULTS

In the OA group, 25.6% of ICAs were located in area 3 and 74.4% in area 2, whereas the percentages were 57.4% and 42.6%, respectively, in the control group. There were 73 (42.4%) ICAs in which the shortest distance between the dorsal surface of the ICA and the ventral cortex of the atlas was less than 4 mm in the OA group and only 50 (29.1%) in the control group. The ideal angulation of C1 screw trajectory was about 5 degrees more medial in the OA group than that in the control group (P < 0.01).

CONCLUSIONS

The risk of ICA injury is much higher in OA patients than in non-OA patients during the C1 screw placement. A mean medial angulation about 20 degrees will permit a long and safe screw purchase, but should be individualized. We recommend careful preoperative computed tomography angiography evaluation in all patients before surgery.

Radiographic and clinical outcomes of C1-C2 intra-articular screw fixation in patients with atlantoaxial subluxation

Background

The Magerl and Goel-Harms techniques have been reported to produce excellent treatment outcomes in cases of atlantoaxial subluxation, but they also carry a risk of vertebral artery injuries. In order to completely prevent such injuries, we developed a surgical procedure, involving bone grafting between the C1 posterior arch and C2 lamina with clamp- or hook-and-rod-based fixation combined with the insertion of an interference screw into the posterior atlantoaxial joint.

Methods

This was a retrospective single-center study. The subjects were 58 patients in whom atlantoaxial subluxation was treated with the abovementioned procedure after 1995 (33 patients with rheumatoid arthritis (RA group) and 25 patients without rheumatoid arthritis (non-RA group)). The clinical outcomes and imaging findings of anterior subluxation at ≥ 2 years after surgery were compared between the RA and non-RA groups.

Results

No vertebral artery injuries occurred during surgery. Seven and two patients died during the follow-up period in the RA and non-RA groups, respectively, but none of these deaths were associated with surgery. At ≥ 2 years after surgery, the visual analogue scale score, Japanese Orthopaedic Association score, and Ranawat classification had significantly improved in both groups (p < 0.001). Radiologically, bone fusion was noted in all patients. Significant changes in the atlas-dens interval (ADI) were seen immediately after surgery in both groups (p < 0.001). In the non-RA group, significant changes in the corrected atlantoaxial height were observed immediately after surgery (p < 0.01), and loss of correction was seen at the final follow-up, but it was not significant (p = 0.1965). No significant changes were noted in any other parameter. Regarding the postoperative alignment of the cervical spine, lordosis tended to decrease, but additional surgery was only performed in one patient, who had developmental stenosis at the mid-lower level and belonged to the RA group. No reoperations due to fused adjacent segmental disease or exacerbated curvature were required.

Conclusion

In the present study, no vertebral artery injuries occurred during surgery, and no major perioperative complications developed. Favorable clinical outcomes were observed at ≥ 2 postoperative years although the patients’ diseases varied. This procedure produced superior outcomes, especially in terms of spinal correction and the maintenance of the ADI.

Comparison of clinical and radiological outcomes between modified Gallie graft fusion-wiring technique and posterior cervical screw constructs for Type II odontoid fractures

The aim of this study was to compare clinical and radiological outcomes between modified Gallie graft fusion-wiring technique and posterior cervical screw constructs for Type II odontoid fractures, and hope to provide references in decision making and surgical planning for both spinal surgeons and surgically treated patients.This is a retrospective study. By retrieving the medical records from January 2005 to July 2015 in our hospital, 53 Type II odontoid fracture patients were reviewed. According to the instrumentation type, patients were divided into 2 groups: Wiring group and Screw group. Three categorized factors were analyzed statistically: patient characteristics: age, body mass index, preoperative neurological status, duration, complicated injuries; surgical variables: surgery time, blood loss, vertebral artery injury, spinal cord or nerve root injury, major systemic complications, wound infection, pain at the bone donor area, instrumentation failure, revision rate; and radiographic parameters: preoperative and final follow-up data of C0-2 curvature, C2-7 curvature, C2-C7 sagittal vertical axis, C7 slope, fracture classification, separation, and displacement of odontoid fracture, fusion rate. An additional comparison of surgical outcomes was done, including patient satisfaction, visual analog scale score for neck pain, neck stiffness, medical expense.There was no statistically significant difference between the 2 groups in patient characteristics of age, sex, body mass index, preoperative neurological status, duration, and complicated injuries. No statistically significant difference was noted in surgical variables of blood loss, vertebral artery injury, spinal cord or nerve root injury, major systemic complications, wound infection, bone harvested zone pain, instrumentation failure, revision rate. The surgery time was shorter in Wiring group than that in Screw group, with a statistically significant difference. We noted no significant difference between the 2 groups when comparing radiographic parameters of preoperative and final follow-up data of C0-2 curvature, C2-C7 sagittal vertical axis, fracture classification, the separation and displacement of odontoid fracture, and fusion rate. Although we noted no significant difference in preoperative C2-7 curvature and C7 slope, the final follow-up data showed that C2-7 curvature and C7 slope were smaller in Wiring group than that in Screw group. We noted no significant difference in visual analog scale score, neck stiffness, and neurological status at final follow-up. The medical expense was less in Wiring group; the patient satisfaction was lower in the Wiring group than that in the Screw group.The modified Gallie graft fusion-wiring technique provided solid fusion and stabilization for patients with Type II odontoid fractures, Gallie graft fusion-wiring resulted in less surgery time, less medical expense, but lower patient satisfaction when compared with the posterior cervical screw constructs.

Surgical anatomy of neurovascular structures related to ventral C1-2 complex: an anatomical study

OBJECTIVE

Transoral odontoidectomy and ventral C1-2 stabilization are important surgical procedures, performed to decompress ventral spinal cord, and to stabilize craniovertebral junction. These procedures require knowledge regarding surgical anatomy of neurovascular structures ventral to the C1-2 complex. The aim of this study is to evaluate the relationships between neurovascular structures and bony landmarks in ventral atlantoaxial complex.

MATERIALS AND METHODS

This study was performed on six formaldehyde fixed cadaveric head and neck specimens. Relevant anatomical parameters, including distances from the midsagittal line to internal carotid arteries (ICA), vertebral arteries (VA), and hypoglossal nerves (HN), were measured using electronic calipers.

RESULTS

The mean distance between ICA and midsagittal line was observed as 26.13 mm at the level of axis and 24.67 mm at the level of the atlas. The mean distance between VA and midsagittal line was observed as 15.38 mm at the level of axis and 26.54 mm at the level of the atlas. The mean distance between HN and midsagittal line was observed as 33.27 and 33.58 mm at the level of the atlas and axis, respectively.

CONCLUSION

This study confirmed that ICA and HN proceeded ventrally or laterally along the lateral aspect of the C1 lateral mass; therefore, the area located ventrally along the medial components of the C1 lateral mass was the safe zone for anterior surgical approach.

Morphometric Study of C1 Pedicle and Feasibility Evaluation of C1 Pedicle Screw Placement with a Novel Clinically Relevant Radiological Classification in an Indian Population

Study Design

A retrospective computed tomography (CT)-based morphometric study of 84 C1pedicles in an Indian population focusing on critical morphometric dimensions vis-a-vis C1 pedicle screw placement.

Purpose

To determine the feasibility of C1 pedicle screw placement in an Indian population and propose a novel classification system for the same.

Overview of Literature

At present, C1 pedicle screws are rarely used, and very few studies have focused on the feasibility of pedicle screw placement in terms of racial, gender, and ethnic variations in anatomical structures. There are no CT-based data on C1 pedicles that assess the feasibility of pedicle screw placement in the Indian population.

Methods

We measured C1 pedicle diameter on CT coronal scan images of 42 adult patients. Extramedullary height (EMH) and intramedullary height (IMH) were measured. We examined the differences between the right and left atlas pedicles and compared measures between males and females. These data were analyzed using significance tests. Based on the results, we propose a novel classification system, which we believe will help in determining the feasibility of C1 pedicle screw placement.

Results

Forty-two adult patients (84 pedicles) were examined. Average EMH and IMH were 4.48±0.91 and 0.86±0.77, respectively. Approximately, 32% of the C1 pedicles had bone thicknesses of <4 mm, 49% had IMH of <1 mm, and 38% had no pedicles. The average thickness in women was 4.21±0.93 mm, which was significantly thinner than that in men (4.73±0.81 mm, p=0.004). Right and left pedicles were not significantly different.

Conclusions

Our data indicate that approximately one-third of the Indian population may not be suitable candidates for C1 pedicle screw placement. Caution should be exercised while placing type 1B and type 2 pedicles based on our proposed classification system.

C1 lateral mass screw insertion from the caudal-dorsal to the cranial-ventral direction as an alternate method for C1 fixation: A quantitative anatomical and morphometric evaluation

OBJECT

C1 lateral mass screw has been widely used for fixation of the upper cervical spine. However, traditional fixation methods are not without complication. Morphometric measurement of an alternative approach is conducted.

METHODS

Three-dimensional CT scans of the cervical spine obtained in 100 adults were evaluated, and key measurements were determined for screw entry points, trajectories, and screw lengths for placement of a C1 screw via this alternate approach. Additional measures were included to account for relevant anatomic variation, including the size of the dangerous lateral zone of the C1 entry point and depth of the atlantooccipital joint surface. Twenty dried atlantal specimens were evaluated to determine corresponding ex vivo measurements.

RESULTS

The mean maximum angle of medialization was 20.8°±2.8° (right) and 21.1°±2.8° (left), as measured in the axial CT images. Sagittal CT images show the mean maximum superior angulation was 24.7°±4.3° (right) and 24°±4.0° (left), and the mean minimum superior angulation was 13.6°±4.4° (right) and 13.6°±3.9° (left). The mean screw length within the lateral mass was 21.2±1.9mm (right) and 21.3±2.0mm (left). Given an additional 10-15mm needed for rod adaptation, an ideal screw length of 30-35mm was determined.

CONCLUSION

The C1 insertion caudally from the C2 nerve root may become an alternate method. Preoperative consideration of the ideal screw insertion point, trajectory, and length are vital for safe and effective surgical intervention.

Is C1 lateral mass screw placement safe for the Chinese, Indians, and Malays? An analysis of 180 computed tomography scans

INTRODUCTION

C1 lateral mass (C1LM) screw is a common procedure in spine surgery. However, related studies are lacking in Asia. We aim to determine the safety of C1LM screw for the Chinese, Indians, and Malays.

METHODS

Three-dimensional computed tomographies of 180 subjects (60 from each ethnic) were analyzed. The length and angulations of C1LM screw and the location of internal carotid artery (ICA) in relation to C1LM were assessed and classified according to the classification by Murakami et al. The incidence of ponticulus posticus (PP) was determined and the differences among the population of these three ethnics were recorded.

RESULTS

The average base length was 8.5 ± 1.4 mm. The lengths within the lateral mass were between 14.7 ± 1.6 mm and 21.7 ± 2.3 mm. The prevalence of PP was 8.3%. 55.3% (199) of ICA were located in zone 0, 38.3% (138) in zone 1-1, 6.4% (23) in zone 1-2, and none in zone 1-3 and zone 2. The average angulation from the entry point to the ICA was 8.5° ± 6.4° laterally. The mean distance of ICA from C1 anterior cortex was 3.7 ± 1.7 mm (range: 0.6∼11.3). There was no difference in distribution of ICA in zone 1 among the three population (Chinese-47%, Indians-61%, and Malays-53%; p > 0.05).

CONCLUSIONS

No ICA is located medial to the entry point of C1LM screw. If bicortical purchase of C1LM screw is needed, screw protrusion of less than 3 mm or medially angulated is safe for ICA. The incidence of PP is 8.3% with higher prevalence among the Indian population.

A prospective, double-blind, randomized controlled trial of treatment of atlantoaxial instability with C1 posterior arches >4 mm by comparing C1 pedicle with lateral mass screws fixation

Background

C1 posterior arch screw placement is one of the most effective treatments for atlantoaxial instability (AAI), which can be performed by either pedicle or lateral mass screw fixation. This study attempted to compare the feasibility and clinical outcomes of C1 pedicle with lateral mass screw fixations for treatment of AAI with C1 posterior arches >4 mm.

Methods

A total of 140 patients with AAI (C1 posterior arches measuring >4 mm) was enrolled in this single-center, randomized, double-blind trial. The subjects were randomly assigned into two treatments: C1 pedicle (group A) or lateral mass (group B) screw fixation. The patients, independent evaluating physicians and radiologists were blinded throughout the entire study. Patients were assessed before operation and in a series of follow-ups at 6 weeks, 6 months, 1 year, and 3 years post-surgery. The operation time, volume of blood loss, intraoperative complications, bone fusion rates, Japanese Orthopaedic Association (JOA) and visual analog scale (VAS) scores were monitored.

Results

All 140 patients showed overall improvements in clinical symptoms after surgery. The mean follow-up time was 24.5 ± 13.0 months. In both groups, the mean JOA scores improved significantly at the time of final follow-up as compared to prior surgery (group A: 7.1 ± 1.4 vs 13.7 ± 1.9; group B:7.3 ± 1.8 vs 13.1 ± 1.4; improvement rates: 87.2 % (group A) and 86.5 % (group B)). The VAS scores also decreased significantly in both groups at the time of final follow-up as compared to prior surgery (group A: 6.0 ± 1.3 vs 1.7 ± 0.8, and group B: 5.7 ± 1.1 vs 2.1 ± 1.2). Bone fusion was achieved within 12 months postoperatively in the patients from both groups. The operation time was significantly shorter and volume of blood loss was significantly less in the patients from group A as compared to group B (p < 0.01). Furthermore, thirteen patients had burst bleeding from the C1-2 venous plexus and nine patients had immediate pain and numbness in the occipitocervical region due to C2 nerve roots irritation during lateral mass screw replacement, which were not observed in the patients with C1 pedicle screw insertion. No complications such as screw loosening, shifting, breakage, or AAI were observed in both groups.

Conclusions

C1 pedicle screw fixation is less invasive and simpler, and has fewer complications. It renders better clinical outcomes than lateral mass screw fixation for treatment of AAI.

Trial registration

Current Controlled Trials ChiCTR-IOR-15006748.

Unilateral C-1 posterior arch screws and C-2 laminar screws combined with a 1-side C1–2 pedicle screw system as salvage fixation for atlantoaxial instability

OBJECT

Atlantoaxial instability often requires surgery, and the current methods for fixation pose some risk to vascular and neurological tissues. Thus, new effective and safer methods are needed for salvage operations. This study sought to assess unilateral C-1 posterior arch screws (PASs) and C-2 laminar screws (LSs) combined with 1-side C1–2 pedicle screws (PSs) for posterior C1–2 fixation using biomechanical testing with bilateral C1–2 PSs in a cadaveric model.

METHODS

Six fresh ligamentous human cervical spines were evaluated for their biomechanics. The cadaveric specimens were tested in their intact condition, stabilization after injury, and after injury at 1.5 Nm of pure moment in 6 directions. The 3 groups tested were bilateral C1–2 PSs (Group A); left side C1–2 PSs with an ipsilateral C-1 PAS + C-2 laminar screw (Group B); and left side C1–2 PSs with a contralateral C-1 PAS + C-2 LS (Group C). During the testing, angular motion was measured using a motion capture platform. Data were recorded, and statistical analyses were performed.

RESULTS

Biomechanical testing showed that there was no significant difference among the stabilities of these fixation systems in flexion-extension and rotation control. In left lateral bending, the bilateral C1–2 PS group decreased flexibility by 71.9% compared with the intact condition, the unilateral C1–2 PS and ipsilateral PAS+LS group decreased flexibility by 77.6%, and the unilateral C1–2 PS and contralateral PAS+LS group by 70.0%. Each method significantly decreased C1–2 movements in right lateral bending compared with the intact condition, and the bilateral C1–2 PS system was more stable than the C1–2 PS and contralateral PAS+LS system (p = 0.036).

CONCLUSIONS

A unilateral C-1 PAS + C-2 LS combined with 1-side C-1 PSs provided the same acute stability as the PS, and no statistically significant difference in acute stability was found between the 2 screw techniques. These methods may constitute an alternative method for posterior atlantoaxial fixation.

The effect of C1 bursting fracture on comparative anatomical relationship between the internal carotid artery and the atlas

PURPOSE

To describe the effect of the C1 bursting fracture on the location of the internal carotid artery (ICA) around the atlas.

METHODS

The authors analyzed the morphology of the atlas and the ICA in 15 patients with C1 bursting fracture and compared with control group (77 patients) without any pathology. All patients were evaluated with CT angiography for the anatomical assessment. The laterality of the ICA, the distances of the ICA from the midline, anterior tubercle, and ventral surface of the C1 lateral mass were compared between two groups. The distance between the lateral margin of the longus capitis muscle and the inner edge of the transverse foramen was also measured.

RESULTS

Medially located ICA was more common in the C1 bursting fracture group than control group (76.7 vs 42.8 %). There were no significant differences between 2 groups for the distance from the midline, anterior tubercle, and ventral surface of the C1 lateral mass, respectively. The distance of the longus capitis muscle to transverse foramen was 2.52 ± 2.09 and 4.15 ± 3.09 mm in each group, and there was statistically significant difference (p < 0.01).

CONCLUSIONS

Lateral displacement of the bony structure of C1 bursting fracture changes the relative location of the ICA medially, which increase the injury risk during the bicortical C1 screw insertion. These data suggest that CT angiography or enhanced CT scans can give critical information to choose the ideal fixation technique and the proper trajectory of the screws for C1 bursting fracture.

Comparison between Bilateral C2 Pedicle Screwing and Unilateral C2 Pedicle Screwing, Combined with Contralateral C2 Laminar Screwing, for Atlantoaxial Posterior Fixation

Study Design

A retrospective study.

Purpose

To compare clinical and radiological outcomes between bilateral C2 pedicle screwing (C2PS) and unilateral C2PS, combined with contralateral C2 laminar screwing (LS), for posterior atlantoaxial fixation.

Overview of Literature

Posterior fixation with C1 lateral mass screwing (C1LMS) and C2PS (C1LMS-C2PS method) is an accepted procedure for rigid atlantoaxial stabilization. However, conventional bilateral C2PS is not always allowed in this method due to anatomical variations of C2 pedicles and/or asymmetry of the vertebral artery. Although unilateral C2PS plus contralateral LS (C2PS+LS) is an alternative in such cases, the efficacy of this procedure has not been evaluated in controlled studies (i.e., with bilateral C2PS as a control).

Methods

Clinical and radiological records of patients who underwent the C1LMS-C2PS method, using unilateral C2PS+LS (n=9), and those treated using conventional bilateral C2PS (n=10) were compared, with a minimum two years follow-up.

Results

Postoperative complications related to the unilateral C2PS+LS technique included one case of spontaneous spinous process fracture of C2. A C1 anterior arch fracture occurred after a fall in one patient, who underwent bilateral C2PS and C1 laminectomy. No significant differences were seen between the groups in reduction of neck pain after surgery or improvement of neurological status, as evaluated using the Japanese Orthopaedic Association score. A delayed union occurred in one patient each of the groups, with the final fusion rate being 100% in both groups.

Conclusions

Clinical and radiological outcomes of unilateral C2PS+LS were comparable with those of the bilateral C2PS fixation technique for the C1LMS-C2PS method.

Aberrant posterior inferior cerebellar artery injury with C1 lateral mass screw placement: a case report and review of the literature

BACKGROUND CONTEXT

Complications associated with C1 lateral mass screw placement are relatively infrequent. The most commonly feared complications include neural or vascular injury. Although both vertebral artery and internal carotid artery injuries have been discussed in the literature, there have been no reports of posterior inferior cerebellar artery (PICA) injury from C1 lateral mass screw placement. We report a case of patient who had a cerebellar stroke after C1 lateral mass screw placement, secondary to injury of an aberrant PICA.

PURPOSE

To describe the normal anatomy of the PICA, the anatomic variations previously reported in the literature, the sequela and symptoms of a patient with PICA injury, and the relevance to C1 lateral mass screw placement. No previous reports of PICA injury with a cerebellar stroke have been reported with C1 lateral mass screw instrumentation.

STUDY DESIGN

Case report and literature review.

METHODS

The patient underwent an Occiput-C6 posterior instrumentation for a pathologic fracture, secondary to multiple myeloma. In the postoperative period, the patient was found to have dysarthria, imbalance, and dysdiadochokinesia. Urgent computed tomography confirmed well placed C1 lateral mass screws. Magnetic resonance imaging/Magnetic Resonance Angiography showed an infarct in the PICA distribution with an abnormal variant of the PICA coursing extracranially around C1. Neurologic monitoring did not detect the injury intraoperatively.

RESULTS

The patient was treated with anticoagulation and he made a reasonable recovery from his stroke.

CONCLUSIONS

We report the first case of an aberrant PICA injured during a C1 lateral mass screw placement, resulting in a cerebellar stroke. Consideration should be given to abnormal PICA variation when placing C1 lateral mass screws.

Biomechanical advantage of C1 pedicle screws over C1 lateral mass screws: a cadaveric study

PURPOSE

The established technique for posterior C1 screw placement is via the lateral mass. Use of C1 monocortical pedicle screws is an emerging technique which utilizes the bone of the posterior arch while avoiding the paravertebral venous plexus and the C2 nerve root. This study compared the relative biomechanical fixation strengths of C1 pedicle screws with C1 lateral mass screws.

METHODS

Nine human C1 vertebrae were instrumented with one lateral mass screw and one pedicle screw. The specimens were subjected to sinusoidal, cyclic (0.5 Hz) fatigue loading. Peak compressive and tensile forces started from ±25 N and constantly increased by 0.05 N every cycle. Testing was stopped at 5 mm displacement. Cycles to failure, displacement, and initial and end stiffness were measured. Finally, CT scans were taken and the removal torque measured.

RESULTS

The pedicle screw technique consistently and significantly outperformed the lateral mass technique in cycles to failure (1,083 ± 166 vs. 689 ± 240 cycles), initial stiffness (24.6 ± 3.9 vs. 19.9 ± 3.2 N/mm), end stiffness (16.6 ± 2.7 vs. 11.6 ± 3.6 N/mm) and removal torque (0.70 ± 0.78 vs. 0.13 ± 0.09 N m). Only 33 % of pedicle screws were loose after testing compared to 100 % of lateral mass screws.

CONCLUSIONS

C1 pedicle screws were able to withstand higher toggle forces than lateral mass screws while maintaining a higher stiffness throughout and after testing. From a biomechanical point of view, the clinical use of pedicle screws in C1 is a promising alternative to lateral mass screws.

C1 lateral mass screw placement via the posterior arch: a technique comparison and anatomic analysis

BACKGROUND CONTEXT

Instrumentation of C1 is becoming increasingly common. Starting points initially described for C1 lateral mass screws at the lateral mass/posterior arch junction are technically challenging. Recently, a number of techniques have evolved advocating varying starting points and trajectories. Despite being technically easier, there are new safety concerns. Insufficient evidence exists for optimal C1 lateral mass screw placement with starting points in the posterior arch.

PURPOSE

To determine anatomic variability of the C1 lateral mass and posterior ring and to compare safety and feasibility of C1 lateral mass screw placement techniques via the posterior arch.

STUDY DESIGN

Descriptive anatomy for surgical technique.

METHODS

One hundred thin-cut cervical spine computed tomography scans were acquired and formatted for virtual surgery. Four different described techniques were used for virtual placement of C1 lateral mass screws. Success was defined as avoidance of critical structures including the transverse foramen, vertebral groove, and spinal dura. Anatomic variability of the C1 vertebra and safe zones for screw placement were also clarified.

RESULTS

Overall screw placement success for the four techniques was 50% (Resnick), 92% (Tan et al.), 58% (Ma et al.), and 85% (Christensen et al.). Average posterior arch height was 6.7±2.1 mm, and vertebral groove height 4.9±1.1 mm was the most limiting dimension to safe screw placement. A safe zone for screw placement was found in 100% of cases (200 screws), 17.0±1.1 mm from midline and a width of 12.6±1.7 mm. Posterior tubercle morphology was variable.

CONCLUSIONS

C1 lateral mass screws could be virtually placed bilaterally in each of 100 clinical cases without violating critical structures. However, none of the previously described approaches worked in every case because of significant anatomic variability. The vertical starting point was particularly critical, and vertebral groove height was the most limiting variable. Although a reliable safe zone could be found in every case, preoperative planning is essential to avoid critical structures.

Incidence and risk factors of the retropharyngeal carotid artery on cervical magnetic resonance imaging

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

Define incidence of anomalous carotid vasculature and associated risk factors as pertains to the anterior approach.

SUMMARY OF BACKGROUND DATA

The carotid artery system, including the common, internal, and external branches, is lateral to the foramen transversarium. If unrecognized, aberrancies in carotid vessel anatomy can lead to devastating complications.

METHODS

A total of 1000 cervical magnetic resonance imagings were screened to localize the carotid artery respective to medial/lateral location of the vessel at each segment from C2-C3 to C6-C7 bilaterally. Vessel location was classified in 3 zones: lateral to the vertebral foramen (type I) (normal); between the lateral foramen and uncoverterbral joint (type II); and medial to the uncovertebral joint (type III). Type III locations were compared with age-matched controls for assessment of cervical alignment via the Ishihara index, C2-C7 angle, and degree of spondylosis.

RESULTS

A total of 123 patients demonstrated carotid artery anomalies (type II and III) (12.3%). Twenty-six patients had type III aberrancy (2.6%). Patients with anomalies were significantly older and more likely to be female (60 vs. 51 yr of age, 74% vs. 57% female, respectively, P < 0.05). The type III group average age was 66.1 years and 88% were female. Aberrancies were more likely right-sided and at C3-C4 or cranial. C2-C7 angle showed significantly greater kyphosis in patients with anomalies compared with controls (6.2 vs. 14.4, P = 0.03). The number of severely spondolytic segments was significantly greater in patients with Type III locations than controls (2.0 vs. 1.1 P < 0.05).

CONCLUSION

Carotid arterial anomalies occurred in 12.3% of cases; severe aberrancy was present in 2.6% of patients. In elderly females with kyphotic alignment, a high index of suspicion must be raised for aberrancy. Preoperative assessment of the vasculature in the anterior neck may avoid catastrophic complications.

Risk of internal carotid artery injury during C1 screw placement: analysis of 160 computed tomography angiograms

BACKGROUND CONTEXT

Injury to the internal carotid artery (ICA) is a potentially catastrophic complication of C1-lateral mass (C1-LM) or C1-C2 transarticular screw insertion.

PURPOSE

This study was designed to determine the risk of injury to the ICA during placement of these screws using computed tomography angiography (CTA).

STUDY DESIGN

Radiographic analysis using CTA.

PATIENT SAMPLE

One hundred sixty CTAs were examined, for a total of 320 ICAs.

OUTCOME MEASURES

Not applicable.

METHODS

Fine-cut intravenous CTAs with multiplanar and three-dimensional reconstruction were reviewed. The position of the ICA in relation to the anterior cortex (AC) of C1, anterior end of the anterior tubercle (AT), and medial margin of the transverse foramen (TF) was measured bilaterally in three ascending and equidistant levels of the C1-AT.

RESULTS

The position of the ICA in relation to C1 was variable. The average distance between the ICA and the AC of C1 was only 3.7 mm. Furthermore, 96% of the time the posterior margin of the ICA was located posterior to the anteriormost aspect of the anterior C1 tubercle (average distance, 5.4 mm), making the ICA vulnerable to damage if a drill, tap, or screw was inserted to the depth of the anteriormost portion of the AT as seen on a lateral fluoroscopic or radiographic view. The medial margin of the ICA was located medial to the TF (a location potentially vulnerable to injury with bicortical screw placement) less often at the caudal aspect of the C1-AT (54%) than at its middle or cranial aspect (74% and 75%, respectively). No ICAs were located anterior to the medial 30% of the C1-LM or more medially.

CONCLUSIONS

Bicortical C1-LM or C1-C2 transarticular screw placement carries a potential risk of ICA injury. Given the wide variation in ICA location relative to C1, if bicortical C1 fixation is required, preoperative CTA should be considered to determine the optimal screw trajectory. In general, inferomedially angulated C1-LM screws appear to be safer with respect to the ICA injury than other potential trajectories.

Posterior fixation of the upper cervical spine: contemporary techniques

Instrumentation in the upper cervical spine has changed considerably in the past two decades. Previous stand-alone wiring techniques have been made largely obsolete with the development of occipital segmental plating, transarticular screws, and C1 lateral mass screws, as well as a myriad of C2 fixation options, including pedicle, pars, and translaminar screws. Polyaxial screws and segmental fixation are more user-friendly than stand-alone wiring and provide a stronger construct. Awareness of the risks and benefits associated with the use of modern instrumentation and thorough familiarity with the anatomy of the upper cervical spine are essential to avoid complications and optimize outcomes.

Avaliação da trajetória dos parafusos bicorticais pela técnica de harms e melcher em relação à artéria carótida interna: estudo experimental em cadáveres

OBJETIVO: O objetivo deste trabalho é estudar, em peças anatômicas; a relação entre os parafusos bicorticais pela técnica de Harms e Melcher e a artéria carótida interna. MÉTODOS: Nossa amostra consiste em cinco cadáveres. RESULTADOS: Os resultados encontrados foram: a média da menor distância entre o orifício de saída do parafuso e a borda medial da artéria carótida interna direita foi de 11,55 mm (com variação de 10,05 a 14,23 mm), enquanto do lado esquerdo a média foi de 7,50 mm (variando de 2,75 a 12,42 mm). A média da menor distância entre a borda posterior da artéria carótida interna e a cortical anterior da massa lateral de C1 à direita foi de 4,24 mm (variando de 2,08 a 7,48 mm), enquanto do lado esquerdo a média obtida foi de 2,98 mm (com variação de 1,83 a 3,83 mm). CONCLUSÃO: Os resultados encontrados estão de acordo com os estudos similares existentes na literatura que enfatizam a necessidade de uma avaliação imaginológica criteriosa da posição anatômica da artéria carótida interna antes da utilização de parafusos bicorticais na massa lateral de C1 por via posterior.

C1 lateral mass screw insertion with protection of C1-C2 venous sinus: technical note and review of the literature

STUDY DESIGN

This is a technical note and review of the literature.

OBJECTIVE

We propose to describe a revised surgical technique of C1 lateral mass screw insertion with protection of C1-C2 venous sinus surrounding the C2 nerve root.

SUMMARY OF BACKGROUND DATA

During C1 lateral mass screw insertion and in posterior C1-C2 fixation, iatrogenic injury of C1-C2 venous sinus results in bleeding, which is troublesome. Appropriate management of the venous sinus in this region is critical to successful surgery in this complex anatomic region.

METHODS

We reviewed 48 patients who underwent posterior C1-C2 fixation at our institution between September 2001 and October 2008. Twenty-four atlas screws were inserted by the originally described C1 lateral mass screw technique (group A), and 28 through a revised posterior arch and lateral mass screw technique (C1 transpedicular screw) (group B). The final group of 44 atlas screws was placed with our newly revised technique (group C).

RESULTS

Bleeding of venous sinus was encountered in 3 group A, 2 group B, and 1 group C atlas screw insertions. The incidence rate was 12.50% (A), 7.14% (B), and 2.27% (C). Statistical comparison showed no significant difference between the groups. All the cases were followed for a mean period of 28.1 month. Four patients in group A complained of postoperative numbness in occipitocervical region. No patients in group B or group C voiced this complaint. A high fusion rate was found in all 3 groups with no signs of implant failure.

CONCLUSION

Bleeding of C1-C2 venous sinus is vigorous and frustrating. The revised technique we describe provides theoretical and practical protection of venous sinus. In addition, the firm bony purchase of screws afforded by this technique contributes to achieving stabilization of the upper cervical spine and a high fusion rate.

Type II odontoid fractures in the elderly: an evidence-based narrative review of management

Considerable controversy exists regarding the optimal management of elderly patients with type II odontoid fractures. There is uncertainty regarding the consequences of non-union. The best treatment remains unclear because of the morbidity associated with prolonged cervical immobilisation versus the risks of surgical intervention. The objective of the study was to evaluate the published literature and determine the current evidence for the management of type II odontoid fractures in elderly. A search of the English language literature from January 1970 to date was performed using Medline and the following keywords: odontoid, fractures, cervical spine and elderly. The search was supplemented by cross-referencing between articles. Case reports and review articles were excluded although some were referred to in the discussion. Studies in patients aged 65 years with a minimum follow-up of 12 months were selected. One-hundred twenty-six articles were reviewed. No class I study was identified. There were two class II studies and the remaining were class III. Significant variability was found in the literature regarding mortality and morbidity rates in patients treated with and without halo vest immobilisation. In recent years several authors have claimed satisfactory results with anterior odontoid screw fixation while others have argued that this may lead to increased complications in this age group. Lately, the posterior cervical (Goel-Harms) construct has also gained popularity amongst surgeons. There is insufficient evidence to establish a standard or guideline for odontoid fracture management in elderly. While most authors agree that cervical immobilisation yields satisfactory results for type I and III fractures in the elderly, the optimal management for type II fractures remain unsolved. A prospective randomised controlled trial is recommended.

The effect of patient age on the internal carotid artery location around the atlas

OBJECT

The aim of this study was to analyze the exact location of the internal carotid artery (ICA) relative to the C-1 lateral mass and describe the effect of age on the tortuosity of the ICA.

METHODS

The authors analyzed 641 patients who had undergone CT angiography to evaluate the location of the ICA in relation to the C-1 lateral mass. Each patient was assigned to 1 of 3 age groups (< 41 years, 41-60 years, and > 60 years of age). The degree of lateral positioning of the ICA was classified into 4 groups: Group 1 (lateral to the C-1 lateral mass), Group 2 (lateral half of the lateral mass), Group 3 (medial half of the lateral mass), or Group 4 (medial to the lateral mass). The anteroposterior relationship of the ICA was classified into Group A (posterior to the anterior tubercle) or Group B (anterior to the anterior tubercle). Distances from the ICA to the midline, anterior tubercle, and anterior cortex of the lateral mass were measured. Distances between the lateral margin of the lateral mass and the longus capitis muscle were also evaluated.

RESULTS

The prevalence of the ICA located in front of the lateral mass (Groups 2 and 3) was 47.4% overall. The position of the ICA changes with age due to vessel tortuosity. Only 18.3% of patients in the youngest age group (< 41 years of age) had an ICA in front of the lateral mass (Group 2 or 3 area). However, this percentage increased in the older 2 groups (43.5% in the 41-60 year old group, and 57% in the > 60-year-old age group). The mean distance from the midline to the ICA was 22.6 mm, and the mean distance from the ICA to the C-1 anterior tubercle and the ventral cortex of the lateral mass was 4.7 and 4.5 mm, respectively. Moreover, the ICA is more prone to injury during bicortical C-1 screw placement when the longus capitis muscle is hypotrophic and does not cover the entire ventral surface of the lateral mass.

CONCLUSIONS

Elderly patients have a higher incidence of a medially located ICA that may contribute to the risk of injury to the ICA during bicortical C-1 screw or C1-2 transarticular screw placement. Although the small number of reported cases of ICA injury does not allow for determination of a direct relationship with specific anatomical characteristics, the presence of unfavorable anatomy does warrant serious consideration during evaluation for C-1 screw placement in elderly patients.

An alternate method for placement of C-1 screws

Object

Several techniques for the surgical stabilization of the atlas and the axis have been described. Placement of C-1 lateral mass screws is one of the latest technical advances, and has gained popularity due to its efficacy and biomechanical advantages. However, the technique for placement of C-1 lateral mass screws, as first described by Harms, can cause excessive bleeding or irritation of the C-2 nerve. An alternative technique is available for the placement of C-1 lateral mass screws that completely avoids the C-2 nerve/ganglion and its associated venous plexus. This new technique mitigates some of the risk associated with the Harms techniques and eliminates the need to use specialized screws (that is, smooth shanks).

Methods

Twenty-six patients underwent atlantoaxial or occipitocervical fusions incorporating the alternative technique of C-1 screw placement. Three surgeons at 3 different institutions performed the surgeries. Standard lateral fluoroscopy and fully threaded polyaxial screws were used in each case.

Results

Forty-nine screws were placed in C-1 lateral masses by using the new technique. Solid arthrodesis was achieved in all cases, with a mean follow-up period of 30 months. There were no cases of CSF leakage, new neurological deficit, injury to the C-2 ganglion, vertebral artery injury, or hardware failures.

Conclusions

The technique is a safe and effective way to fixate C-1 while avoiding the C-2 nerve/ganglion and venous plexus. The results indicate that excellent clinical and radiographic outcomes can be achieved with this new technique.

C1 lateral mass anatomy: Proper placement of lateral mass screws

STUDY DESIGN

Cadaveric specimens were measured to determine appropriate placement for C1 lateral mass screws. Instrumentation guidelines were developed and used to instrument a series of cadaveric specimens. Clinical experience with C1 lateral mass fixation was reviewed to evaluate results. Postoperative computed tomographic (CT) scans were reviewed to evaluate screw placement.

OBJECTIVES

The cadaveric study measured the dimensions of the atlas and determined ideal trajectory for screw placement. This technique was applied clinically, and 50 cases were retrospectively reviewed for fixation difficulties, neurologic or vascular injuries, and perioperative complications. Postoperative CT scans were reviewed when available.

SUMMARY OF BACKGROUND DATA

Halo application, posterior wiring, and C1 to C2 transarticular screws have been used to stabilize the upper cervical spine. Each technique has disadvantages, and C1 lateral mass fixation recently has gained popularity as a potential alternative. Recent anatomic studies have documented the dimensions of the C1 lateral mass and its ability to accommodate screw fixation. Small clinical series have documented early success with this technique.

METHODS

Fifteen specimens were stripped of soft tissue and measured by using calipers and CT scans. Guidelines were formulated for C1 lateral mass screw fixation. Additional specimens with intact soft tissue were instrumented without difficulty. A clinical series was reviewed to evaluate for complications related to this technique. Postoperative CT scans were reviewed to evaluate screw placement.

RESULTS

The C1 lateral mass safely accommodated screw fixation. Trajectory of 10 degrees medial and 22 degrees cephalad was preferred. The technique was safely applied in a series of 50 patients. Postoperative CT scans showed the ability of the surgeon to achieve the intended goals for starting point and safe trajectory.

CONCLUSIONS

C1 lateral mass fixation is a safe alternative for upper cervical fixation with several potential advantages versus other techniques, but further clinical evaluation is warranted.

SAFE ZONE FOR C1 LATERAL MASS SCREWS

OBJECTIVE

To evaluate the possible complications of overpenetrated C1 lateral mass screws and to identify and define a “safe zone” area anterior to the C1 vertebra.

METHODS

The study was performed on 10 cadavers and 50 random patients who had undergone computed tomographic scanning with contrast medium of the neck for other purposes. Atlas lateral mass screw trajectories were plotted, and the safe zone for screw placement anterior to the atlas vertebra was determined for each trajectory.

RESULTS

The trajectory of the internal carotid artery was measured from its medial wall. The trajectory of the internal carotid artery according to the ideal entrance point of the screw was 11.55 ± 4.55 degrees (range, 2–22 degrees) in the cadavers and 9.78 ± 4.55 degrees (range, −5 to 22 degrees) bilaterally in the patients. At 15 degrees (ideal screw trajectory), the thickness of the rectus capitis anterior muscle and longus capitis muscle was 6.69 ± 0.83 mm (range, 5.32–7.92 mm) in the cadavers and 7.29 ± 1.90 mm (range, 0.50–13.63 mm) bilaterally in the patients. The smallest distance from the internal carotid artery to the anterior cortex of the C1 vertebra was calculated as 4.33 ± 2.03 mm (range, 1.15–8.40 mm) bilaterally in the cadavers and 5.07 ± 1.72 mm (range, 2.15–8.91 mm) bilaterally in radiological specimens.

CONCLUSION

The internal carotid artery trajectory is lateral to the ideal entrance point of C1 lateral mass screws. The medial angulation of a screw placed in the lateral mass of C1 seemed to increase the margin of safety for the internal carotid artery. The rectus capitis anterior and longus capitis muscles may be thought of as a safe zone area for C1 lateral mass screws. At more than 25 degrees of medial angulation, the risk of perforation of the oropharyngeal wall increases.

Ideal screw entry point and projection angles for posterior lateral mass fixation of the atlas: an anatomical study

Although various posterior insertion angles for screw insertion have been proposed for C1 lateral mass, substantial conclusions have not been reached regarding ideal angles and average length of the screw yet. We aimed to re-consider the morphometry and the ideal trajections of the C1 screw. Morphometric analysis was performed on 40 Turkish dried atlas vertebrae obtained from the Department of Anatomy at the Medical School of Ankara University. The quantitative anatomy of the screw entry zone, trajectories, and the ideal lengths of the screws were calculated to evaluate the feasibility of posterior screw fixation of the lateral mass of the atlas. The entry point into the lateral mass of the atlas is the intersection of the posterior arch and the C1 lateral mass. The optimum medial angle is 13.5 +/- 1.9 degrees and maximal angle of medialization is 29.4 +/- 3.0 degrees . The ideal cephalic angle is 15.2 +/- 2.6 degrees , and the maximum cephalic angle is 29.6 +/- 2.6 degrees . The optimum screw length was found to be 19.59 +/- 2.20 mm. With more than 30 degrees of medial trajections and cephalic trajections the screw penetrates into the spinal canal and atlantooccipital joint, respectively. Strikingly, in 52% of our specimens, the height of the inferior articular process was under 3.5 mm, and in 70% was under 4 mm, which increases the importance of the preparation of the screw entry site. For accommodation of screws of 3.5-mm in diameter, the starting point should be taken as the insertion of the posterior arch at the superior end of the inferior articular process with a cephalic trajection. This study may aid many surgeons in their attempts to place C1 lateral mass screws.

C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities

STUDY DESIGN

In vitro biomechanical study.

OBJECTIVE

To compare the pullout strengths and the biomechanical stabilities afforded by C1 lateral mass screws and C1 pedicle screws using bicortical and unicortical fixation techniques.

SUMMARY OF BACKGROUND DATA

Posterior screw fixation techniques in the atlas including C1 lateral mass screw and C1 pedicle screw. The shortcomings of C1 lateral mass screw technique and potential risks of bicortical fixation method were recently described; C1 pedicle screw technique with unicortical fixation might overcome these anatomic and clinical drawbacks. However, it is unknown whether the biomechanical characteristics of unicortical C1 pedicle screw are comparable with that of bicortical C1 lateral mass screw. METHODS.: Bicortical or unicortical C1 pedicle screws and C1 lateral mass screws were inserted into 12 adult fresh human C1 specimens. Pullout strength was evaluated using a material testing machine. The construct's stability of bicortical C1 lateral mass screws or unicortical C1 pedicle screws incorporating unicortical C2 pedicle screws was compared with bilateral transarticular screws using another 6 fresh cervical cadaver spines. Pullout strength and biomechanical stability differences were compared statistically.

RESULTS

Bicortical C1 pedicle screws provided the biggest pullout strength (1757.0 +/- 318.7 N) of all 4 methods, whereas unicortical C1 lateral mass screws provided the weakest(794.5 +/- 314.8 N). However, there were no statistically significant differences between bicortical C1 lateral mass screws (1243.8 +/- 350.0 N) and unicortical C1 pedicle screws (1192.5 +/- 172.6 N). Furthermore, there was no statistically significant difference of biomechanical construct stability between unicortical C1 pedicle screw-rod constructs and bicortical C1 lateral mass screw-rod constructs.

CONCLUSION

C1 pedicle screws are stiffer than C1 lateral mass screws. Unicortical C1 pedicle screw provided the same pullout resistance and three-dimensional stability as bicortical C1 lateral mass fixation. Although lateral mass screw placement into C1 requires bicortical purchase, pedicle screw insertion into the atlas only requires unicortical fixation.

Estudo anatômico dimensional do arco posterior de C2 para a instrumentação com parafuso intralaminar

INTRODUÇÃO: A articulação atlantoaxial possui mecanismos estabilizadores C1-C2, ligamentares, ósseos e capsulares, mantendo a relação anatômica adequada entre C1 e C2. A falha, traumática ou atraumática, isolada ou um conjunto destes mecanismos leva à instabilidade atlantoaxial, podendo culminar em alterações neurológicas, dor e limitação da mobilidade cervical. Casos com déficit neurológico e de instabilidade moderada a grave, são passíveis de tratamento cirúrgico. Desde 1910 inúmeras técnicas de estabilização cirúrgica C1-C2 são praticadas e mesmo recentemente novas técnicas de estabilização C1-C2 vêm sendo desenvolvidas. Novas técnicas foram desenvolvidas utilizando parafusos bilaterais na massa lateral de C1 e na lâmina de C2, conectados por barras. OBJETIVO: Mensurar as dimensões da lâmina de C2 para avaliar a segurança e dimensão do parafuso a ser utilizado, pela técnica de Wright. MÉTODOS: Estudo anatômico com 29 cadáveres adultos dissecando a lâmina de C2, aferindo medidas externa e interna da lâmina no plano sagital, coronal e axial. RESULTADOS: A média das medidas das porções médias externas das lâminas de C2 foi 5,83 mm, das quais 8,93% foram abaixo de 3,5mm. CONCLUSÃO: Sugerimos um estudo tomográfico pré-operatório, para identificar pacientes com lâminas menores e logo em maior risco.

Vertebral artery injury in cervical spine surgery: anatomical considerations, management, and preventive measures

BACKGROUND CONTEXT

Vertebral artery (VA) injury can be a catastrophic iatrogenic complication of cervical spine surgery. Although the incidence is rare, it has serious consequences including fistulas, pseudoaneurysm, cerebral ischemia, and death. It is therefore imperative to be familiar with the anatomy and the instrumentation techniques when performing anterior or posterior cervical spine surgeries.

PURPOSE

To provide a review of VA injury during common anterior and posterior cervical spine procedures with an evaluation of the surgical anatomy, management, and prevention of this injury.

STUDY DESIGN

Comprehensive literature review.

METHODS

A systematic review of Medline for articles related to VA injury in cervical spine surgery was conducted up to and including journal articles published in 2007. The literature was then reviewed and summarized.

RESULTS

Overall, the risk of VA injury during cervical spine surgery is low. In anterior cervical procedures, lateral dissection puts the VA at the most risk, so sound anatomical knowledge and constant reference to the midline are mandatory during dissection. With the development and rise in popularity of posterior cervical stabilization and instrumentation, recognition of the dangers of posterior drilling and insertion of transarticular screws and pedicle screws is important. Anomalous vertebral anatomy increases the risk of injury and preoperative magnetic resonance imaging and/or computed tomography (CT) scans should be carefully reviewed. When the VA is injured, steps should be taken to control local bleeding. Permanent occlusion or ligation should only be attempted if it is known that the contralateral VA is capable of providing adequate collateral circulation. With the advent of endovascular repair, this treatment option can be considered when a VA injury is encountered.

CONCLUSIONS

VA injury during cervical spine surgery is a rare but serious complication. It can be prevented by careful review of preoperative imaging studies, having a sound anatomical knowledge and paying attention to surgical landmarks intraoperatively. When a VA injury occurs, prompt recognition and management are important.

Posterior fixation and fusion with atlas pedicle screw system for upper cervical diseases

OBJECTIVE

To evaluate the feasibility, safety and efficacy of atlas pedicle screws system fixation and fusion for the treatment of upper cervical diseases.

METHODS

Twenty-three consecutive patients with upper cervical disorders requiring stabilization, including 19 cases of atlantoaxial dislocation (4 congenital odontoid disconnections, 6 old odontoid fractures, 4 fresh odontoid fractures of Aderson II C, 3 ruptures of the C(1) transverse ligament, and 2 fractures of C(1)), 2 cases of C2 tumor (instability after the resection of the tumors), and 2 giant neurilemomas of C(2)-C(3)(instability after resection of the tumors), were treated by posterior fixation and fusion with the atlas pedicle screw system, in which the screws were inserted through the posterior arch of C1. The operative time, bleeding volume and complications were reported. All patients were immobilized without external fixation or with rigid cervical collars for 1-3 months. All patients were followed up and evaluated with radiographs and CT.

RESULTS

In the 23 patients, 46 C(1) pedicle screws, 42 C(2) pedicle screws and 6 lower cervical lateral mass screws and 2 lower cervical pedicle screws were placed. The mean operative time and bleeding volume was 2.7 hours and 490 ml respectively. No intraoperative complications were directly related to surgical technique. No neurological, vascular or infective complications were encountered. All patients were followed up for 3-36 months (average 15 months). Firm bony fusion was documented in all patients after 3-6 months. One patient with atlas fracture showed anterior occipitocervical fusion. There was no implant failure.

CONCLUSIONS

Posterior fixation and fusion of the atlas pedicle screw system is feasible and safe for the treatment of upper cervical diseases, and may be applicable to a larger number of patients.

Relationship between screw trajectory of C1 lateral mass screw and internal carotid artery

STUDY DESIGN

Evaluation of diagnostic imaging.

OBJECTIVE

To comprehend anatomic relationships between the internal carotid artery (ICA) and bicortical purchase of C1 lateral mass screws from the perspective of avoiding ICA injury.

SUMMARY OF BACKGROUND DATA

No studies have evaluated safety trajectory of atlantal lateral mass screw that would avoid the ICA injury in relation to its location, although previous studies have indicated concern about ICA injury by the screw tip at the anterior surface of the lateral mass of the atlas.

METHODS

From 149 of 177 human 3-dimensional computed tomography reconstruction images, 6 distance and 2 angle parameters related to both atlas and ICA were measured on the plane 15 degrees cephalad to the transverse plane. In addition, angle of error during screw insertion from intended trajectory was checked.

RESULTS

The ICA was located in front of the C1 lateral mass in 64.4% of cases and faced the lateral one third of the C1 lateral mass in 54.6% of cases. None were located in front of the medial one third of the C1 lateral mass. The maximum inward screw trajectory that would violate the ICA was 8.6 degrees . Mean angle of preoperative C1/2 rotation and angle of error from intended trajectory was about 5 degrees , respectively.

CONCLUSION

The possibility of ICA injury can be excluded by correct insertion of the screw 10 degrees inward. Although bicortical purchase with adequately medially angulated trajectory might be safe enough, we must remember the possibility to violate the ICA in bicortical purchase, because the intended screw trajectory never be assured.

Fixation strength of unicortical versus bicortical C1-C2 transarticular screws

BACKGROUND CONTEXT

The internal carotid artery and hypoglossal nerve lie over the anterior aspect of the lateral mass of the atlas and are at risk from bicortical C1-C2 transarticular screws. This has led to the recommendation for unicortical screws if the neurovascular structures are in close proximity to the proposed exit point. No data are available on strength of unicortical versus bicortical C1-C2 transarticular screws.

PURPOSE

To compare the biomechanical pullout strength of unicortical versus bicortical C1-C2 transarticular screws in a cadaveric model.

STUDY DESIGN

Biomechanical study.

METHODS

Fifteen cervical spine specimens underwent axial pullout testing. A unicortical C1-C2 transarticular screw was placed on one side with a contralateral bicortical screw. Data were analyzed to reveal any significant differences in strength.

RESULTS

Mean pullout strength for the bicortical C1-C2 transarticular screws was 1,048.8 (+/-360.1) N versus 939.2 (+/-360.6) for unicortical screws (p=.22). There was no significant difference in the pullout strength of unicortical and bicortical screws.

CONCLUSIONS

In cases with satisfactory bone quality, it appears reasonable to use unicortical screws to avoid the risk of neurovascular injury from penetrating the anterior cortex of C1.