The optimal transarticular c1-2 screw length and the location of the hypoglossal nerve

Perioperative complications associated with fluoroscopy C1 lateral mass screw fixation (Goel technique) versus computed tomography-guided navigation technique: A review of 202 cases from the German Spine Registry (DWG-Register)

Background

Overview of the literature - Fractures of the C1 constitute 3%-13% of all cervical spine injuries in adults. Most isolated C1 fractures are stable and can be treated nonoperatively with external immobilization. Traditional surgical options for C1 fracture treatment are occiput-to-C2 fusion or C1 with lateral mass screws (LMSs). Purpose - The aim is to assess the management and perioperative complications of C1 fractures undergoing LMS fusion between fluoroscopy and computed tomography (CT)-guided navigation.

Methods

This was a retrospective multicenter study of data from the DWG-Register of patients who underwent operative treatment for C1 traumatic fracture with LMSs from January 2017 to September 2022. Inclusion criteria - traumatic injury and age > 18 years old.

Results

In total, 202 patients with traumatic C1 fracture requiring spinal surgery were identified in the registry; n = 175 (Group 1) were treated conventionally without CT-guided navigation and n = 27 were treated with CT-guided navigation (Group 2). C1-LMS was principally performed by spine surgeons n = 90 (53.4%) and n = 72 (18.5%) by neurosurgeons in both the groups. Intraoperative adverse events were as follows: dural tear in group 1 n = 0 and in group 2 n = 1, vascular injury, with one case in group 1 and no cases in group 2. General complications were: cardiovasculars in group 1 n = 6 (3.4%) and Group 2 n = 4 (14.8%) (P = 0.03), pulmonary complications in group1 n = 2 (1.1%) and n = 9 in group 2 (33.3%) (P < 0.001), stroke n = 1 (0.57%) in group1 and n = 4 in group 2 (14.8%) (P < 0.001), gastrointestinal bleeding n = 1 (0.57%) in group1 and no cases in group 2, renal insufficiency n = 2 (1.1%) in group 1 and n = 3 (11.1%) in group 2 (P = 0.01). One death was recorded in group 2 (3.7%).

Conclusion

This series of 404 screws placed in 202 patients over 5 years who underwent two types of C1 fracture fixation had a considerably lower incidence of screw malposition and vertebral artery injury than has previously been reported in the literature. C1 screws can be safely placed with a low risk of vertebral artery and neurologic injury with and without CT-guided navigation support.

Bilateral palsy of the hypoglossal nerve following general anesthesia for emergency surgery. A case report

INTRODUCTION AND IMPORTANCE

Hypoglossal nerve palsy is a rare condition usually associated with tumors, trauma, stroke or multiple sclerosis. It can be associated with other cranial nerve palsies while injury to this nerve typically affects a patient's articulation by causing lingual motility disturbance and swallowing difficulty. Bilateral isolated hypoglossal nerve palsy is an even more infrequent condition, which can occasionally be due to airway manipulation.

CASE PRESENTATION

We describe a case of bilateral hypoglossal nerve damage following general anesthesia for emergency surgery, presenting with dysarthria, immobility of the tongue and dysphagia after extubation. The patient had a gradual recovery of all lost functions during the next four months.

CLINICAL DISCUSSION

Bilateral hypoglossal nerve palsy is a very rare entity and tracheal tube malposition or prolonged but unnoticed tracheal cuff pressure especially in the face of low blood pressure, should be considered as possible causative mechanisms for this condition. This underlines the importance of careful positioning of the patient's head and neck during surgery as well as the meticulous and correct performance of routine maneuvers of airway management.

CONCLUSION

Bilateral hypoglossal nerve palsy is a very rare entity. Diagnosis and management of twelfth nerve palsy require a multidisciplinary approach to achieve the best patient outcome.

Anthropometric evaluation for surgical feasibility of C1-C2 transarticular screw stabilization in Indian population

Study Design:

This study was a radiographic observational study for C1–C2 anthropometry.

Purpose:

The purpose of the study was to understand the anatomic relationship of C1–C2 in view of transarticular screw (TAS) fixation, to overcome the difficulties related with TAS placement, and to minimize the technique-related complications.

Materials and Methods:

It was an anthropometric observational study with retrospectively obtained anatomical data of randomly selected 116 patients from a single center. The anatomical measurements such as pars width, pars height, screw trajectory, and length were evaluated on the axial, sagittal, and three-dimensional reconstructed cervical CT scan using the radiant DICOM viewer software by the two fellowship trained spine surgeons which were blind to the study group details. The intra- and interobserver reliability with regard to the measured parameters was statistically analyzed.

Results:

The mean age of male and female was 28 and 29 years. The average BMI was calculated to be 23.5 and 25 for males and females, respectively. The mean right pars width in males was 5.78 ± 0.93 (range: 3.1–6.5 mm), while in female, it was 5.84 ± 0.95 (range: 3.1–6.5). The mean left pars width in males was 5.95 ± 1.13 (range: 3.8–8.1 mm), while in females, it was 5.70 ± 1.18 (range: 3.7–8.1 mm). Right side mean pars height in males was 5.90 ± 1.2 (range: 3.7–9.4 mm), and in females, it was 6.11 ± 1.04 (range: 3.8–9.3 mm). Left-sided mean pars height in males was 6.0 ± 1.1 (range: 3.2–9.4 mm) as compared to females, in which it was 5.77 ± 1.23 (range: 4.1–9.3 mm). The mean lateral angulation angle in males was 9.99° ± 1.70° (8.1°–15°), while in females, it was 10.15° ± 1.73° (8.1°–15°). The mean sagittal angulation in males was 26.33° ± 3.32° (21.0°–32.80°), while in females, it was 27.18 ± 3.05 (21.0°–32.10°). The average screw length in males was 41.74 ± 5.63 (34–54.8 mm), whereas in females, it was 41.35 ± 4.77 (34–54.8 mm).

Conclusion:

This study provides a morphometric database which is characteristic of the C1–C2 vertebrae in the normal Indian population with regard to the anatomic feasibility of the TAS fixation for various C1–C2 pathologies. The C2 pars width and height measured in the current study can guide the selection of TAS screws in the Indian population. This study could serve in providing the baseline anatomic parameters assessed in the healthy individuals to design and develop customized screws and related implant assembly which might provide wider clinical applicability.

Basilar invagination: A mimicker of bulbar-onset amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by progressive onset motor deficits with heterogenous presentations ranging from dysarthria to foot drop. Approximately 20% of the patients present with focal bulbar symptoms, in which some may remain restricted to bulbar region (isolated bulbar palsy), and the remaining eventually spreads to involve other body regions (classical ALS). Without accompanying upper and lower motor neurons signs elsewhere, differential diagnoses for isolated bulbar symptoms are extensive, include ALS variants as well as potentially treatable mimics. Therefore, it is important to take heed on every possible aetiology that may disrupt the hypoglossal nucleus, nerve, or lingual muscle itself. Herein, we illustrated a rare presentation of Group A basilar invagination, which mimicked bulbar-onset ALS.

Bilateral Hypoglossal Nerve Palsy After Occipitocervical Fusion

A 63-year-old man sustained a Jefferson fracture and was treated nonoperatively by a separate treating surgeon. Because of the symptomatic malalignment and nonunion after 6 months of nonsurgical management, the patient was seen for a second opinion. Occiput to C3 arthrodesis was performed. Postoperatively, the patient was diagnosed with a bilateral hypoglossal nerve palsy. Hypoglossal nerve injuries after cervical spine fractures and posterior cervical procedures are a very rare occurrence. This is the first case report of a bilateral hypoglossal nerve palsy following occipitocervical arthrodesis.

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.

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.

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.

Hypoglossal Nerve Palsy After Cervical Spine Surgery

STUDY DESIGN

Multi-institutional retrospective study.

OBJECTIVE

The goal of the current study is to quantify the incidence of 2 extremely rare complications of cervical spine surgery; hypoglossal and glossopharyngeal nerve palsies.

METHODS

A total of 8887 patients who underwent cervical spine surgery from 2005 to 2011 were included in the study from 21 institutions.

RESULTS

No glossopharyngeal nerve injuries were reported. One hypoglossal nerve injury was reported after a C3-7 laminectomy (0.01%). This deficit resolved with conservative management. The rate by institution ranged from 0% to 1.28%. Although not directly injured by the surgical procedure, the transient nerve injury might have been related to patient positioning as has been described previously in the literature.

CONCLUSIONS

Hypoglossal nerve injury during cervical spine surgery is an extremely rare complication. Institutional rates may vary. Care should be taken during posterior cervical surgery to avoid hyperflexion of the neck and endotracheal tube malposition.

C1 Lateral Mass Screw Migration Causing a Delayed Unilateral Hypoglossal Nerve Lesion: A Case Report

CASE

We present the case of a fifty-eight-year-old woman who was initially treated with a C1 to C7 anterior-posterior cervical decompression and fusion for an epidural abscess and returned two years postoperatively with four days of progressive dysphagia and tongue deviation. She was diagnosed with a unilateral hypoglossal nerve (cranial nerve XII) palsy secondary to compression from a C1 lateral mass screw.

CONCLUSION

This is the first reported case that we are aware of describing a delayed cranial nerve palsy secondary to cutout and cephalad migration of a C1 lateral mass screw resulting in a neurologic deficit due to impingement on the hypoglossal nerve.

Subarachnoid hemorrhage and acute hydrocephalus as a complication of C1 lateral mass screws

STUDY DESIGN

Case report.

OBJECTIVE

To present a previously unreported complication of subarachnoid hemorrhage and hydrocephalus after C1 lateral mass screw insertion. To inform spine specialists of this potential postoperative complication.

SUMMARY OF BACKGROUND DATA

Damage to the carotid artery, vertebral artery, hypoglossal nerve and dural tears are all recognized complications. Acute hydrocephalus as a result of subarachnoid hemorrhage is not previously reported.

METHODS

A 63-year-old female with a traumatic C1 ring and C2 peg fracture underwent C1-C2 fixation. During insertion of the C1 lateral mass screws there was significant hemorrhage from the C1-C2 venous plexus. Three days postoperatively, she developed headache, confusion, and became drowsy.

RESULTS

Computed tomographic scan of the brain revealed hydrocephalus and intraventricular blood that was managed with an external ventricular drain.

CONCLUSION

The case of acute hydrocephalus due to intraventricular hemorrhage from C1 lateral mass screw placement has not previously been reported. Surgeons performing the procedure should consider the diagnosis if patients display signs of raised intracranial pressure postoperatively.

LEVEL OF EVIDENCE

N/A.

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.

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.

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.

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.

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.

Anatomical relationship of the internal carotid artery to C-1: clinical implications for screw fixation of the atlas

Object

Various C1–2 instrumentation techniques have been developed to treat atlantoaxial instability. Screw fixation of C1–2 poses a risk of injury to the vertebral artery and internal carotid artery (ICA). Injury to the ICA caused by C-1 screws is extremely rare, but has been described. To characterize this risk, the authors studied the anatomical relationship of the ICA to the lateral mass of C-1.

Methods

The authors studied 100 patients who had undergone computed tomography scanning and magnetic resonance imaging of the neck to assess the position of the ICA in association with the C-1 lateral mass. Each ICA was classified into 1 of the following 4 zones: Zone 1 (medial to lateral mass), Zone 2 (medial half of lateral mass), Zone 3 (lateral half of lateral mass), and Zone 4 (lateral to lateral mass). For patients with an ICA ventral to the lateral mass, the shortest distance between the ICA and lateral mass was measured to determine the margin of error with an overpenetrated bicortical screw.

Results

Of the 100 patients, 58% had a left ICA in Zones 2 and 3 with a mean distance from the anterior cortex of 3.5 ± 1.5 mm (± standard deviation), and 74% had a right ICA in Zones 2 and 3 with a mean distance from the anterior cortex of 3.9 ± 1.6 mm. Both ICAs anterior to the lateral mass were noted in 47% of patients, and 84% had ≥ 1 ICA anterior to the lateral mass. When the ICA was anterior to the lateral mass, it was more commonly in the lateral half (left ICA in 91% and right ICA in 92%). The left ICA was in Zone 1 in 1% and Zone 4 in 41%. The right ICA was in Zone 1 in 1% and Zone 4 in 25%.

Conclusions

A high percentage of patients demonstrate an ICA directly ventral to the C-1 lateral mass, which poses a risk of ICA injury caused by an overpenetrated bicortical screw.

Relationship of the internal carotid artery to the anterior aspect of the C1 vertebra: implications for C1-C2 transarticular and C1 lateral mass fixation

STUDY DESIGN

Anatomic study of the internal carotid artery (ICA) location with respect to C1 based on computed tomography (CT) scans with contrast medium.

OBJECTIVE

To measure the location of the ICA relative to the anterior aspect of C1 to assess the risk of placing C1-C2 transarticular or C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

Vertebral artery injury is a known risk from placement of screws in C1. A previous case report revealed an ideally placed C1-C2 transarticular screw abutting and narrowing the ICA. The risk of ICA injury from C1 screws is unknown.

METHODS

Fifty random head and neck CT scans with contrast medium were retrospectively analyzed. Measurements were taken bilaterally including the closest distance from the ICA lumen to C1 and the distance from the medial edge of the ICA to a line drawn along the medial border of the foramen transversarium. The risk of inserting bicortical C1-C2 transarticular and C1 lateral mass screws was estimated based on these measurements.

RESULTS

The mean distance from the ICA to C1 was 2.88 mm on the left and 2.89 mm on the right. The ICA lumen was medial to the foramen transversarium in 42 (84%) of 50 cases (mean: 2.78 mm on the left and 3.00 mm on the right). The proximity of the ICA to C1 posed moderate risk in 46% of cases and high risk in 12% (on at least one side).

CONCLUSION

Because of the risk of ICA injury from a drill bit or the tip of a bicortical screw, we recommend preoperative CT scan with contrast medium in all cases in which a screw is to be placed into C1. If the ICA is in close proximity to the anterior border of C1, unicortical fixation or a different fusion technique should be considered.

Biomechanical Comparison of Unicortical Versus Bicortical C1 Lateral Mass Screw Fixation

STUDY DESIGN

Biomechanical study of pullout strength of unicortical versus bicortical C1 lateral mass screws using a cadaveric cervical spine model.

OBJECTIVE

To compare pullout strength of unicortical versus bicortical C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

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 lateral mass screws. Unicortical screws would reduce the risk of injury to these neurovascular structures; however, no data are available on the relative strength of unicortical versus bicortical C1 lateral mass screws.

METHODS

Fifteen cadaveric cervical spine specimens underwent axial pullout testing of C1 lateral mass screws. A unicortical C1 lateral mass screw was placed on 1 side with a contralateral bicortical screw.

RESULTS

The mean pullout strengths of the unicortical screws and bicortical screws were 588 N (range, 212 to 1234 N) and 807 N (range, 163 to 1460 N), respectively (P=0.008).

CONCLUSIONS

Bicortical C1 lateral mass screws were significantly stronger than unicortical screws; however, the mean pullout strength of both the unicortical and bicortical C1 screws were greater than previously reported values for subaxial lateral mass screws. On the basis of these data, the clinical necessity for using bicortical screw fixation in all patients must be questioned. If similar strength can be achieved using unicortical C1 lateral mass screw to that currently accepted in the subaxial spine, bicortical screws might not be justified for the C1 lateral mass. However, the ability to extrapolate C1-C2 data to subaxial spine data is uncertain because of the difference in normal physiologic loading at these levels.

C1 anatomy and dimensions relative to lateral mass screw placement

STUDY DESIGN

An anatomic surface osteometric analysis of cadaveric cervical spines.

OBJECTIVE

To assess the feasibility of placing a 3.5-mm cortical screw in the lateral mass of C1 in a large number of specimens for the purpose of gaining internal fixation for various conditions.

SUMMARY OF BACKGROUND DATA

Previous studies have addressed surface dimensions of the atlas vertebra and computerized tomography-measured dimensions of the lateral masses of the atlas. These studies used a limited number of specimens with potentially homogeneous origins.

METHODS

A total of 120 atlas (C1) vertebrae for a total of 240 lateral masses were examined and external measurements obtained to assess the feasibility of placing a 3.5-mm cortical screw in the lateral mass.

RESULTS

The minimum lateral mass dimensions found from 240 C1 lateral masses were 13.15 mm anterior-posterior, 4.22 mm medial-lateral, and 4.73 mm cephalocaudal. The height of the posterior arch at the groove for the vertebral artery (pedicle analog) was less than 4 mm in 46 of 240 (19.2%) arches.

CONCLUSIONS

It is feasible to safely and reproducibly place a 3.5-mm cortical screw in the lateral mass of C1 when the appropriate starting point and trajectory of the screw are chosen.

Hypoglossal nerve palsy after posterior screw placement on the C-1 lateral mass. Case report

Atlantoaxial fixation in which C1-2 screw-rod fixation is performed is a relatively new method. Because reports about this technique are rather scant, little is known about its associated complications. In this report the authors introduce hypoglossal nerve palsy as a complication of this novel posterior atlantoaxial stabilization method. A 67-year-old man underwent a C1-2 screw-rod fixation for persistent neck pain resulting from a Type 2 odontoid fracture that involved disruption of the transverse atlantal ligament. Posterior instrumentation in which a C-1 lateral mass screw and C-2 pedicle screw were placed was performed. Postoperatively, the patient suffered dysphagia with deviation of the tongue to the left side. At the 4-month follow-up examination, bone fusion was noted on plain x-ray studies of the cervical spine. His hypoglossal nerve palsy resolved completely 2 months postoperatively. To the authors' knowledge, this is the first report in the literature of hypoglossal nerve palsy following C1-2 screw-rod fixation. The hypoglossal nerve is one of the structures that can be damaged during C-1 lateral mass screw placement.

Anterior retropharyngeal fixation C1-2 for stabilization of atlantoaxial instabilities: study of feasibility, technical description and preliminary results

Posterior transarticular screw fixation C1-2 with the Magerl technique is a challenging procedure for stabilization of atlantoaxial instabilities. Although its high primary stability favoured it to sublaminar wire-based techniques, the close merging of the vertebral artery (VA) and its violation during screw passage inside the axis emphasizes its potential risk. Also, posterior approach to the upper cervical spine produces extensive, as well as traumatic soft-tissue stripping. In comparison, anterior transarticular screw fixation C1-2 is an atraumatic technique, but has been neglected in the literature, even though promising results are published and lectured to date. In 2004, anterior screw fixation C1-2 was introduced in our department for the treatment of atlantoaxial instabilities. As it showed convincing results, its general anatomic feasibility was worked up. The distance between mid-sagittal line of C2 and medial border of the VA groove resembles the most important anatomic landmark in anterior transarticular screw fixation C1-2. Therefore, CT based measurements on 42 healthy specimens without pathology of the cervical spine were performed. Our data are compiled in an extended collection of anatomic landmarks relevant for anterior transarticular screw fixation C1-2. Based on anatomic findings, the technique and its feasibility in daily clinical work is depicted and discussed on our preliminary results in seven patients.

Virtual placement of posterior C1-C2 transarticular screw fixation

We wanted to evaluate how often safe and effective posterior C1-C2 transarticular screw placement is realizable when it is performed according to guidelines given in the literature. In 50 adult patients, computerized tomography scan data from C0 to C3 were transformed into a 3D spine model. Virtually, bilateral screws were placed from the medial third of the C2-C3 facet joint towards the rim of the C1 anterior arc parallel to midline. Three categories of virtual screw position were rated: optimal (virtual screw inside the C2 pars interarticularis, transversing the middle third of the atlantoaxial joint, and sparing the vertebral artery canal), suboptimal (virtual screw violating the C2 pars interarticularis, and/or transversing the lower or upper third of the C1-C2 joint, and sparing vertebral artery canal), and unacceptable (virtual screw breaching the vertebral artery canal). Optimal placement was seen in 74, suboptimal placement in 11, and unacceptable locations in 15 sites. We conclude that due to the variability of the anatomy of the upper cervical spine, optimal transarticular C1-C2 screw placement is not possible in up to 26%, and even hazardous in up to 15%.

Frameless Stereotactic Image-Guided C1-C2 Transarticular Screw Fixation for Atlantoaxial Instability

OBJECTIVE

We retrospectively studied 20 adults who underwent C1-C2 transarticular screw (TAS) fixation utilizing frameless stereotaxy.

METHODS

The study group comprised 13 men and 7 women, with a mean age of 63 years (range 12-87 years). All patients demonstrated clinical and radiographic evidence of C1-C2 instability. The cause of the instability was trauma in 11 patients, rheumatoid arthritis in 6 patients, failed prior surgery in 2 patients, and congenital malformation in 1 patient. All patients underwent stabilization with C1-C2 TASs using image-guided frameless stereotaxy.

RESULTS

There were no new or worsening neurologic symptoms reported at 18-month follow-up. Motor weakness improved in seven of nine patients, myelopathy in seven of seven, and gait in three of six patients in whom these deficits were present preoperatively. Postoperative complications included one surgical site abscess, one cutaneous pressure ulcer, and one iliac crest donor site infection. Of 36 screws placed, 33 (92%) were well positioned. Normal C1-C2 alignment was achieved in 17 of 20 (85%) patients. In 4 of 20 cases, screw implant, which was thought to be anatomically difficult, if not impossible, on the basis of routine magnetic resonance or computed tomography imaging, was actually accomplished successfully using surgical navigation.

CONCLUSIONS

C1-C2 TAS placement is a safe and accurate surgical technique that may improve neurologic function. Use of intraoperative navigation can facilitate achieving difficult surgical trajectories that match the patient's anatomy, thus allowing TAS implant in patients who otherwise would not be candidates for this type of internal fixation.

An anatomical study comparing standard fluoroscopy and virtual fluoroscopy for the placement of C1–2 transarticular screws

Object. The authors sought to compare radiation exposure, surgical time, and accuracy of screw placement when using either standard fluoroscopy or virtual fluoroscopy for the placement of C1–2 transarticular screws.

Methods. Twenty-two C1–2 transarticular screws were placed in 11 cadavers in a randomized and alternating order by using either standard fluoroscopy or virtual fluoroscopy (fluoronavigation). The radiation time, procedure time, and accuracy of screw placement were recorded and statistically compared. A small but statistically significant reduction in fluoroscopy time was noted with the virtual fluoroscopy technique but the surgical times were similar between the two techniques. The incidence of noncritical and critical breaches (those at risk of causing a neurovascular injury) was not significantly different between the two groups. Careful analysis of the C1–2 anatomy in these specimens underscored the importance of placing the screw path in a maximally dorsal and medial portion of the C-2 isthmus to avoid injury to the vertebral artery and to maximize the bone purchase of the C-1 lateral mass.

Conclusions. Although virtual fluoroscopy may represent a useful tool for transarticular screw placement, it does not supplant traditional surgical techniques and does not appear to lower the incidence of bone breaches that can occur when performing this demanding procedure.

Multiplanar reconstructions of helical computed tomography in planning of atlanto-axial transarticular fixation

The objective of this study was to determine atlanto-axial bone morphometric measurements related to screw transarticular fixation technique. One hundred helical computerized tomography (helical CT) scans with volumetric acquisition, including the first and the second cervical vertebrae, were studied. The screw insertion axis according to the Magerl technique for C1-C2 transarticular fixation was the referential to select the correct oblique axial and oblique parasagittal planes obtained with multiplanar reconstruction (MPR) on helical CT. The selected measured parameters on each side of the vertebrae were C2 interarticular isthmus height and width, optimal screw length, optimal screw trajectory sagittal and axial angles, and the distance between the ideal screw trajectory and the vertebral artery groove. C2 interarticular isthmus height measured 7.75+/-1.27 mm, C2 interarticular isthmus width 7.94+/-1.72 mm, optimal screw length 39.03+/-2.81 mm, optimal screw trajectory sagittal angle 57.54+/-5.28 degrees , optimal screw trajectory medial angle 7.90+/-4.05 degrees. Isthmus narrowing under 5 mm (height and/or width) was seen in 5% of cases. In 30% of cases reconstructed parasagittal images showed the vertebral artery groove. In those cases, the distance between the vertebral artery groove and the ideal screw path was measured. This distance measured under 2.5 mm in 7% of C2 articular masses. A classification of C2 articular mass morfology was proposed. The C2 articular masses without anatomic variations predisposing to vertebral artery injury were considered type I. The C2 articular masses potentially associated with vascular injury (12%) were classified as type II. Potential risk was identified at the C2 isthmus only (3%), at the anterior portion of C2 articular mass only (7%) or at both regions (2%). According to selected criteria 18% of patients would have at least one side C2 articular mass with potential risk for the vertebral artery. In 6% of patients the potential risk was identified bilaterally. There is a great variation in the maximum and minimum values of the anatomic measurements. Therefore preoperative CT scans are very important to identify type II cases, such that the surgeon may preoperatively define the bony anatomy trough which the screws will pass.

Posterior Instrumentation Surgery for Craniocervical Junction Instabilities: an Update

The surgical treatment of craniocervical junction (CCJ) instability has recently undergone significant development and change. Posterior instrumentation surgery has been the mainstay of treatment of CCJ instability, and is the focus of this review. For the treatment of atlantoaxial instability, C1-2 transarticular screw fixation has shown good stability, and has been regarded as the "gold standard" procedure. Because of potentially hazardous complications including vertebral artery injury, however, C-1 lateral mass-C-2 pedicle screw fixation is gaining popularity. For treatment of atlantooccipital instability, occipitocervical fixation using screw constructs (combined with either rods or plates) has shown more stability than sublaminar wiring techniques, and has been utilized more frequently. Both innovation in material engineering and in vitro biomechanical studies have contributed significantly to the development of more rigid internal fixation devices, and as a result, many patients who would have been treated conservatively with external orthosis are treated nowadays with instrumentation surgery, resulting in earlier ambulation, shortened hospital stay, and earlier recovery into social activities. New surgical techniques and instruments, however, need to stand the test of time to see whether they are free from long-term adverse events. The rapid turnover of new surgical techniques and hardware has made it difficult for less experienced surgeons to keep up with the latest developments. Conventional techniques can be safer and less technically demanding than newer techniques for those who are not familiar with them.

Acute atlanto-axial post-operative subluxation following posterior C1/2 fusion

Two cases referred with acute post-operative C1/2 subluxation following posterior fusion are reported. Both cases had initial treatment for atlanto-axial instability with posterior cable (Brooks and interspinous) and graft techniques, and placed immediately in a Philadelphia collar. One case was found to have subluxed immediately post-operatively when failing to breathe following reversal of anaesthetic agents, and despite immediate realignment and reoperation was left with a significant quadriparesis. The other patient was noted to have subluxed on routine X-ray on day 4, and had no neurological deficit before or after reoperation. Risk factors for this dangerous complication are discussed and the techniques of C1/2 posterior fusion and stabilization are reviewed in detail. Surgeons performing atlanto-axial stabilization procedures should be familiar with and have expertize in the complete range of techniques described and choose the one most appropriate for the patient's individual requirements.

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

STUDY DESIGN

A case of internal carotid artery impingement by the tip of a well-positioned C1-C2 transarticular screw is presented along with a pilot study involving radiologic and anatomic evaluation of human cadaveric specimens.

OBJECTIVE

To raise awareness that the internal carotid artery may be in close proximity to the anterior aspect of the atlas and at risk of injury during placement of C1-C2 transarticular screws or C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

To our knowledge, no cases of internal carotid artery injury or impingement have been reported with screw fixation of the atlas.

METHODS

A case of internal carotid artery impingement by a C1-C2 transarticular screw is presented. The C1-C2 rotation appeared to place the internal carotid artery in the path of the screw, prompting a pilot study. Three fresh-frozen human cadaveric head and neck specimens were fixed in different degrees of rotation. Thin-section computed tomography of the specimens was obtained in the plane of the atlas. The frozen specimens were sectioned in the same plane as the computed tomography images. Measurements were taken to assess the location of the internal carotid artery relative to the anterior aspect of the atlas.

RESULTS

Cervical rotation does not have a predictable effect on the location of the internal carotid artery. Medial angulation of a screw placed in the lateral mass of C1 appears to increase the margin of safety for the internal carotid artery. The internal carotid artery varies in location and may be within 1 mm of the ideal exit point of a bicortical transarticular screw or a C1 lateral mass screw.

CONCLUSIONS

The internal carotid artery is at risk during bicortical screw fixation of the atlas. We recommend a contrast-enhanced computed tomography to assess the location of the internal carotid artery before screw fixation of the atlas.

Effect of frameless stereotaxy on the accuracy of C1-2 transarticular screw placement

OBJECT

In recent studies some authors have indicated that 20% of patients have at least one ectatic vertebral artery (VA) that, based on previous criteria in which preoperative computerized tomography (CT) and standard intraoperative fluoroscopic techniques were used. may prevent the safe placement of C1-2 transarticular screws. The authors conducted this study to determine whether frameless stereotaxy would improve the accuracy of C1-2 transarticular screw placement in healthy patients, particularly those whom previous criteria would have excluded.

METHODS

The authors assessed the accuracy of frameless stereotaxy for C1-2 transarticular screw placement in 17 cadaveric cervical spines. Preoperatively obtained CT scans of the C-2 vertebra were registered on a stereotactic workstation. The dimensions of the C-2 pars articularis were measured on the workstation, and a 3.5-mm screw was stereotactically placed if the height and width of the pars interarticularis was greater than 4 mm. The specimens were evaluated with postoperative CT scanning and visual inspection. Screw placement was considered acceptable if the screw was contained within the C-2 pars interarticularis, traversed the C 1-2 joint, and the screw tip was shown to be within the anterior cortex of the C-1 lateral mass. Transarticular screws were accurately placed in 16 cadaveric specimens, and only one specimen (5.9%) was excluded because of anomalous VA anatomy. In contrast, a total of four specimens (23.5%) showed significant narrowing of the C-2 pars interarticularis due to vascular anatomy that would have precluded atlantoaxial transarticular screw placement had previous nonimage-guided criteria been used.

CONCLUSIONS

Frameless stereotaxy provides precise image guidance that improves the safety of C1-2 transarticular screw placement and potentially allows this procedure to be performed in patients previously excluded because of the inaccuracy of nonimage-guided techniques.