The location of the pedicle and pars interarticularis in the axis

What is the C2 pedicle, pars interarticularis, and isthmus? Anatomical study and review of the literature regarding these confusing terms with proposal of new nomenclature

INTRODUCTION

The atypical anatomy of the C2 vertebra has led to terminological discrepancies within reports and studies in the literature regarding the location of its pedicle, pars interarticularis, and isthmus. These discrepancies not only limit the power of morphometric analyses, but they also confuse technical reports regarding operations involving C2, and thus confuse our ability to properly communicate this anatomy. Herein, we examine the variations in nomenclature regarding the pedicle, pars interarticularis, and isthmus of C2, and via an anatomical study, propose new terminology.

METHODS

The articular surface and underlying superior and inferior articular processes and adjacent transverse processes were removed from 15 C2 vertebrae (30 sides). Specifically, the areas regarded as the pedicle, pars interarticularis, and isthmus were evaluated. Morphometrics were performed.

RESULTS

Our results indicate that, anatomically, C2 has no "isthmus" and that a pars interarticularis for C2, when present, is very short. Deconstruction of the attached parts allowed for visualization of a bony arch extending from the anterior most aspect of the lamina to the body of C2. The arch is composed almost entirely of trabecular bone and without its attached parts, e.g., transverse process, really has no cortical bone laterally.

CONCLUSIONS

We propose a more accurate terminology, the pedicle, for pars/pedicle screw placement of C2. Such a term more accurately describes this unique structure of the C2 vertebra and would alleviate terminological confusion in the future literature on this topic.

Proposal of Treatment Strategy for Pedicle Fractures of the C2: An Analysis of 49 Cases

Spine surgeons often confuse C2 pedicle fractures (PFs) with pars interarticularis fractures. In addition, little information is available about the characteristics and treatment strategies for C2 PFs. We sought to investigate the characteristics of C2 PFs and to propose an appropriate treatment strategy. A total of forty-nine patients with C2 PFs were included in this study. We divided these patients into unilateral and bilateral C2 PF groups. The incidence rates and characteristics of other associated C2 and C2-3 injuries, and other cervical injuries, were evaluated. In addition, treatment methods and outcomes were analyzed. Twenty-two patients had unilateral C2 PFs and twenty-seven patients had bilateral C2 PFs. Among the cases of unilateral C2 PFs, all patients had one or more other C2 fractures, and twenty patients (90.9%) had one or two C2 body fractures. Meanwhile, among the cases of bilateral C2 PF, all patients had two or more other C2 fractures and one or two C2 body fractures. In unilateral C2 PFs, three patients with C2-3 anterior slip or adjacent cervical spine (C1-3) injury underwent surgery and nineteen patients (86.4%) were treated with conservative methods. In bilateral C2 PFs, three patients with C2-3 anterior slip or SCI at C2-3 underwent surgery and twenty-four patients (88.9%) were treated with conservative methods. Our results showed that C2 PFs do not occur alone and are always accompanied by other associated C2 injuries. C2 PFs should, generally, be thought of as a more complex fracture type than hangman's fracture or dens fracture. Despite the complex fracture characteristics, most C2 PFs can be managed with conservative treatment. However, surgical treatments should be considered if the C2 PFs are accompanied by the C2-3 anterior slip and adjacent cervical spine injury.

ANATOMICAL EVALUATION OF THE PEDICLE OF THE AXIS THROUGH COMPUTERIZED TOMOGRAPHY IN ADULTS

ABSTRACT Objectives: The topography of the high cervical spine involves several traumatic, degenerative, and rheumatologic pathologies. With the evolution of surgical techniques and synthesis materials available for use in such region, an optimization of the anatomical understanding of this area is required. Methods: Therefore, this study evaluated 62 computed tomographies of the high cervical spine in an adult population, aiming at the study of the anatomical parameters of the axis pedicle. The measures analyzed in this observational study were pedicle length at axial section, pedicle length at sagittal section, pedicle thickness at axial section and interpedicular angulation. Results: Computed tomography is a necessary exam for the programming of C2 pedicle screws and is useful for determining the anatomical changes and evaluating the length of the screws that will be used. Furthermore, no statistically significant difference was observed in the length, angulation, and diameter of the pedicles of the axis in relation to sex or age. Conclusion: Regarding sex and age, no statistically significant difference on length, angulation, and pedicle diameter occur. There is an urgent need for computed tomography for surgical planning. Level of Evidence II; Transversal Diagnostic Studies – Investigation of a Diagnosis Test.

Axis screws: results and complications of a large case series

OBJECTIVE

To present the surgical results of patients who underwent axis screw instrumentation, discussing surgical nuances and complications of the techniques used.

METHODS

Retrospective case-series evaluation of patients who underwent spinal surgery with axis instrumentation using screws.

RESULTS

Sixty-five patients were included in this study. The most common cause of mechanical instability was spinal cord trauma involving the axis (36 patients - 55.4%), followed by congenital craniocervical malformation (12 patients - 18.5%). Thirty-seven (57%) patients required concomitant C1 fusion. Bilateral axis fixation was performed in almost all cases. Twenty-three patients (35.4%) underwent bilateral laminar screws fixation; pars screws were used in twenty-two patients (33.8%), and pedicular screws were used isolated in only three patients (4.6%). In fourteen patients (21.5%), we performed a hybrid construction. There was no neurological worsening nor vertebral artery injury in this series.

CONCLUSION

Axis screw instrumentation proved to be a safe and efficient method for cervical stabilization. Laminar and pars screws were the most commonly used.

A New Entrance Technique for C2 Pedicle Screw Placement and the Use in Patients With Atlantoaxial Instability

STUDY DESIGN

A prospective study and a technique note.

OBJECTIVES

To introduce a new entrance technique for C2 pedicle screw placement and to measure the related linear and angular parameters about the entrance point on computed tomography (CT) images. The safety of this technique for patients with atlantoaxial instability was also evaluated.

BACKGROUND DATA

Although earlier studies have introduced different methods for C2 pedicle screw placement, the entry points and the angular parameters may be variable. Few studies have established a fixed entry point on the basis of the anatomic structure of C2 for pedicle screw placement.

METHODS

A total of 60 dry C2 vertebrae were obtained for anatomic measurement in the study. The posterior bilateral nutrient foramens of C2 lamina were selected as the entry points for pedicle screw placement. The foramens were marked with needles and then the vertebrae underwent CT scan. The axial and sagittal planes of C2 pedicles were harvested and 4 linear and 2 angular parameters about the entry point were determined. After that, we used the entrance technique on 31 patients with atlantoaxial instability in a prospective study. CT of the cervical spine was performed to evaluate the safety of the entrance technique.

RESULTS

The nutrient foramens exist in 97% of the left lamina and 93% of the right lamina of the C2 vertebra. The overall mean distance from the entry point (nutrient foramen) to the superior border of lamina (PSD), to the inferior border of lamina (PID), to the medial border of the pedicle (PMD), and the length of pedicle screw trajectory (PL, transit the pedicle center) were 3.32±0.63, 8.33±1.21, 6.85±1.00, and 24.47±1.51, respectively. The averaged transverse angle (α) on the axial plane and the superior angle (β) on the sagittal plane were 19.83±3.83 and 30.12±6.02 degrees, respectively. Then, 31 patients underwent bilateral C2 pedicle screw fixation without screw violation into the spinal canal or vertebral artery injury by the new entrance technique. The overall mean angles α and β and the length of the pedicle screw were 17.52±3.81 and 34.29±4.18 degrees and 25.85±2.06 mm, respectively. No statistical differences were found in these 3 parameters between the dry C2 vertebrae and the C2 vertebrae of patients who underwent the surgery (P>0.05).

CONCLUSIONS

Using the posterior bilateral nutrient foramens of the C2 lamina as the entry point is a helpful intraoperative landmark for C2 pedicle screw placement.

Surgical Intervention for Unstable Craniovertebral Junction Anomalies with Narrow C2 Pedicle

OBJECTIVE

We sought to investigate and report a novel surgical technique of screws insertion and posterior surgical reduction, as well as explore its clinical results.

METHODS

From September 2008 to September 2012, we treated 41 cases of unstable craniovertebral junction anomalies with a narrow C₂ pedicle at our department. All patients underwent "posterior reduction and internal fixation of the occipital bone with superior or inferior articular process of C₂ and lateral mass of C₃ on the narrowed C₂ pedicle side-for non-narrowed C₂ pedicle side, the screw was only inserted into C₂ pedicle without extending the fixation to C₃ vertebrae-using a titanium screw-rod (plate) fixation system." The preoperative and postoperative atlantodens interval, Chamberlain line, McRae line, and cervicomedullary angle were all measured. In addition, the preoperative and postoperative Japanese Orthopedic Association score was used to evaluate the cervical myelopathy.

RESULTS

A total of 134 screws were inserted into the C₂ pedicle (30 screws), superior (35 screws) or inferior (17 screws) articular process of C₂, and lateral mass of C₃ (52 screws). There was a significant statistical difference between the preoperative and postoperative results in the reduction of the odontoid process, decompression of the upper cervical spinal cord and medulla, as well as the improvement of neurologic functions (P < 0.05). All patients have exhibited a major neurologic improvement and solid bony fusion.

CONCLUSION

This novel surgical technique is safe, feasible, and effective for the treatment of unstable craniovertebral junction anomalies with a narrow C₂ pedicle.

CT analysis of anatomical variation and injury affecting posterior pedicle screw fixation for unstable Hangman fractures

The aim of this study was to evaluate the anatomical variations and injuries in patients with unstable Hangman fractures that affected the posterior pedicle screw placement of C2 to C3 and retrospectively review our experience with management of these fractures. Clinical data were reviewed in 72 patients with unstable Hangman fractures, especially using 3-dimensional computed tomography (3D-CT) scan to identify the presence of anatomical variations or injuries and analyzing the treatment strategies we used. Twenty-two patients (22/72, 30.6%) with 39 (C2 or C3) risk factors were not fit for safe C2 to C3 pedicle screw placement, due to factors such as small pedicle size of C2 or C3, high-riding vertebral arteries, fractured fragments encased into vertebral canal, or transverse process foramen of C2, sclerotic pedicles and pedicle fractures of C3. One or more than one of these risk factors could pose more risks of arterial or neural structures damages to pedicle screw fixation for unstable Hangman fractures. Individualized treatment plans were made to minimize the risks of surgery for the 22 patients. There is a high incidence of anatomical variations and injuries in the C2 to C3 region in patients with unstable Hangman fractures that affect the pedicle screw placement. Preoperative evaluation of these conditions using 3D-CT scans is of paramount importance to avoid and decrease operative complications and to choose appropriate surgical techniques.

New entry point for C2 screw, in posterior C1-C2 fixation (Goel-Harm's technique) significantly reducing the possibility of vertebral artery injury

OBJECTIVE

To reduce the chance of vertebral artery injury in posterior C1 lateral mass and C2 pedicle/pars screw-rod fixation (Goel-Harms technique ).

METHOD

49 patients, 30 males and 19 females, 12years - 82 years, underwent posterior C1-C2 fixation from February 2007 till June2013. A new entry point for the posterior C2 screw, 3mm below the midpoint of the C1-C2 joint which is directed medially and downwards into the C2 body , probably avoids the vertebral artery. As the screw now bypasses the pedicle/ pars , the chance of injuring the vertebral artery is probably reduced.

RESULTS

No case of intra-operative vertebral artery injury.

CONCLUSION

The new technique of C2 screw fixation allows rigid immobilization of the C1-C2 joint without significant risk of vertebral artery injury.

Surgical Intervention for Instability of the Craniovertebral Junction

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

Direct C2 Pedicle Screw Fixation for Axis Body Fracture

BACKGROUND

Acute complex C2 vertebral body fracture specifically does not involve the odontoid process or C2 pars interarticularis. External stabilization can be effective but may prolong healing and increase morbidity. Many traditional surgical techniques can achieve internal stabilization at the expense of normal cervical motion. We describe direct surgical C2 pedicle screw fixation as an option for managing acute complex C2 vertebral body fracture.

CASE DESCRIPTION

Three patients were treated with direct pedicle screw fixation of acute traumatic complex C2 vertebral body fractures. All fractures were coronally oriented Benzel type 1. None of the patients sustained neurological injury. Stereotactic navigation with intraoperative computed tomography scanning was used for each procedure. Surgery provided immediate internal orthosis and stability, as judged by intraoperative dynamic fluoroscopy. Rigid cervical collar bracing was used for 1 month after surgery when the patients were out of bed. Initial radiographs showed acceptable screw placement and fracture alignment. Dynamic radiographs at 3 months showed structural stability at the fracture site and adjacent levels, and complete bony union was confirmed with late computed tomography scanning (>1 year) in each case. Each patient reported resolution of trauma-related and postsurgical pain at 30-day follow-up. Postoperative Neck Disability Index questionnaires for each patient suggested no significant disability at 1 year.

CONCLUSIONS

Direct pedicle screw fixation of acute complex C2 vertebral body fracture appeared to be safe and effective in our 3 patients. It may provide a more-efficient and less-morbid treatment than halo brace or cervical collar immobilization in some patients.

[Are C2 pedicles always screwable? Calibration and planning with a pedicle-lamina angle]

INTRODUCTION

Posterior cervical arthrodesis is associated with osteosynthesis. C2 pedicular screwing affords a good bone anchoring but involves neurological and vascular risks.

PURPOSE

To determine C2 pedicular screwing feasibility from a large cohort of cervical CT scans. To describe the visible anatomical parameters during a surgical procedure in order to plan and secure it.

MATERIALS AND METHODS

Retrospective consecutive series of 100 cervical CT scans was analyzed. Cases with upper cervical fracture were excluded. C2 surgical anatomy was assessed according to maximum length, minimum width and minimum height. Angular parameters were pedicle-transverse angle and sagittal angle. Original pedicle-lamina angle was used as a visible mark during the procedure independent of the patient's position. Pedicular screwing feasibility was evaluated. It was arbitrarily defined by a lower minimum height less than 4mm.

RESULTS

Two hundred C2 pedicles were analyzed with 7.5% that were not screwable. Their mean length was 26.2mm, with a mean width of 5.2mm and a mean height of 9.2mm. Mean pedicle-transverse angle was 36.2°, mean sagittal angle was 25.8° and mean pedicle-lamina angle was 81.3°.

CONCLUSION

C2 pedicle screwing feasibility is inconstant due to anatomical variability. In fact, 13% of patients have at least one non-screwable pedicle. Preoperative planning is essential to achieve this procedure. A pedicle-lamina angle can be used which remains independent from the patient's position.

Detailed description of anatomy of the fracture line in hangman's injury: a retrospective observational study on motor vehicle accident victims

OBJECTIVE

To study the precise location of fracture line in hangman's fracture to determine the fracture patterns, symmetry and involvement of different vertebral elements.

METHODS

32 cases of hangman's fractures were retrospectively evaluated. All patients presented with motor vehicle accidents. CT scans were studied to accurately localize the fracture lines. Symmetry of fracture lines on both sides was assessed, and involvement of the vertebral bodies, lamina, facet joints and foramen transversarium was also determined.

RESULTS

20 patients showed asymmetric fracture locations, 13 of them had a unilateral pedicle fracture and a contralateral pars fracture which comprised the most common injury pattern (40% of cases). Less frequent combinations for the two sides of asymmetric C2 ring disruption include pars-vertebral body (3 patients), pedicle-vertebral body (2 patients) and pedicle-lamina (2 patients). 12 patients showed symmetrical fractures (5 through the pars and 7 through the pedicles). Vertebral body and facet joint involvement were demonstrated in 15 (47%) and 16 (50%) cases, respectively. 18 cases had fractures extending into the foramen transversarium (56%). In total, 26 fracture lines primarily affected the pars (40%) and 31 affected the pedicles (49%).

CONCLUSION

Asymmetric hangman's fracture is more common with the usual pattern being fracture pedicle on one side and pars on the other followed by the symmetric bilateral pedicle and bilateral pars fractures. Fracture lines running into the transverse foramen and facet joints are very frequent as well as those involving the vertebral bodies.

ADVANCES IN KNOWLEDGE

There is controversy in literature regarding the fracture locations in hangman's injury owing to lack of studies that address this subject. This article is the first to describe precisely the anatomical locations and patterns of this injury.

Feasibility of CT-based intraoperative 3D stereotactic image-guided navigation in the upper cervical spine of children 10 years of age or younger: initial experience

OBJECT Rigid screw fixation may be technically difficult in the upper cervical spine of young children. Intraoperative stereotactic navigation may potentially assist a surgeon in precise placement of screws in anatomically challenging locations. Navigation may also assist in defining abnormal anatomy. The object of this study was to evaluate the authors' initial experience with the feasibility and accuracy of this technique, both for resection and for screw placement in the upper cervical spine in younger children. METHODS Eight consecutive pediatric patients 10 years of age or younger underwent upper cervical spine surgery aided by image-guided navigation. The demographic, surgical, and clinical data were recorded. Screw position was evaluated with either an intraoperative or immediately postoperative CT scan. RESULTS One patient underwent navigation purely for guidance of bony resection. A total of 14 navigated screws were placed in the other 7 patients, including 5 C-2 pedicle screws. All 14 screws were properly positioned, defined as the screw completely contained within the cortical bone in the expected trajectory. There were no immediate complications associated with navigation. CONCLUSIONS Image-guided navigation is feasible within the pediatric cervical spine and may be a useful surgical tool for placing screws in a patient with small, often difficult bony anatomy. The authors describe their experience with their first 8 pediatric patients who underwent navigation in cervical spine surgery. The authors highlight differences in technique compared with similar navigation in adults.

Posterior Reduction of Fixed Atlantoaxial Dislocation and Basilar Invagination by Atlantoaxial Facet Joint Release and Fixation: A Modified Technique With 174 Cases

BACKGROUND:

Treatment of fixed atlantoaxial dislocation (AAD) with basilar invagination (BI) is challenging.

OBJECTIVE:

To introduce a modified technique to reduce fixed AAD and BI through a posterior approach.

METHODS:

From 2007 to 2013, 174 patients with fixed AAD and BI underwent surgical reduction by posterior atlantoaxial facet joint release and fixation technique.

RESULTS:

There was 1 death in the series, and 3 patients were lost to follow-up. The follow-up period ranged from 12 to 52 months (mean: 35.2 months) for the remaining 170 patients. Neurological improvement was observed in 168 of 170 patients (98.8%), and was stable in 1 (0.06%) and exacerbated in 1 (0.06%), with the Japanese Orthopedic Association scores increasing from 11.4 preoperatively to 15.8 postoperatively (P &lt; .01). Radiologically, complete or &gt;90% reduction was attained in 107 patients (62.9%), 60% to 90% reduction was attained in 51 patients (30%), and &lt;50% reduction was attained in 12 patients (7.1%), who underwent additional transoral decompression. Complete decompression was demonstrated in all 170 patients. Solid bony fusion was demonstrated in 167 patients at follow-up (98.2%).

CONCLUSION:

This series showed the safety and efficacy of the posterior C1-2 facet joint release and reduction technique for the treatment of AAD and BI. Most fixed AAD and BI cases are reducible via this method. In most cases, this method avoids transoral odontoidectomy and cervical traction. Compared with the occiput-C2 screw method, this short-segment C1-2 technique exerts less antireduction shearing force, guarantees longer bone purchase, and provides more immediate stabilization.

A new technique in the surgical treatment of Hangman's fractures: Neurospinal Academy (NSA) technique

Context:

Treatment of Hangman's fractures is still controversial. Hangman's fractures Type II and IIA are usually treated with surgical procedures.

Aim:

This study aims at describing the Neurospinal Academy (NSA) technique as an attempt to achieve an approximation of the fracture line to the axis body, which may be used for Type II and IIA patients with severe displacement and angulation.

Settings and Design:

NSA technique both pars or pedicle screws are placed bicortically to ensure that anterior surface of C2 vertebral body will be crossed 1-2 mm. A rod is prepared in suitable length and curve to connect the two screws. For placing the rod, sufficient amount of bone is resected from the C2 spinous process. C2 vertebral body is pulled back by means of the screws that crossed the anterior surface of C2 vertebral body.

Materials and Methods:

Hangman II and IIA patient are treated with NSA technique.

Result:

Angulated and tilted C2 vertebral body was pulled back and approximated to posterior elements.

Conclusions:

In Hangman's fractures Type II and IIA with severe vertebral body and pedicle displacement, NSA technique is an effective and reliable treatment alternative for the approximation of posterior elements to the C2 vertebral body, which is tilted, angulated, and dislocated.

Comparison of fatigue strength of C2 pedicle screws, C2 pars screws, and a hybrid construct in C1-C2 fixation

STUDY DESIGN

A biomechanical study comparing the fatigue strength of different types of C2 fixation in a C1-C2 construct.

OBJECTIVE

To determine the pullout strength of a C2 pedicle screw and C2 pars screw after cyclical testing and differentiate differences in stiffness pre- and post-cyclical loading of 3 different C1-C2 fixations.

SUMMARY OF BACKGROUND DATA

Some surgeons use a short C2 pars screw in a C1-C2 construct, because it is less technically demanding and/or when the vertebral artery is high riding. Difference in construct stiffness between use of bilateral C2 pedicle screws, bilateral C2 pars screws, or a hybrid construct is unknown.

METHODS

Biomechanical testing was performed on 15 specimens. A bicortical C1 lateral mass screw was used in combination with 1 of 3 methods of C2 fixation: (1) bilateral long C2 pedicle screws (LL), (2) bilateral 14-mm C2 pars screws (SS), and (3) unilateral long C2 pedicle screw with a contralateral 14-mm C2 pars screw (LS). Each construct was subject to 16,000 cycles to simulate the immediate postoperative period. Changes in motion in flexion-extension, lateral bending, and axial rotation were calculated. This was followed by pullout testing.

RESULTS

The ability to limit range of motion significantly decreased after cyclical testing in flexion-extension, lateral bending, and axial rotation for all 3 groups. After loading, the LL and LS groups had less percentage of increase in motion in flexion-extension and lateral bending than the SS group. Overall, the average pullout strength of a pedicle screw was 92% stronger than a pars screw.

CONCLUSION

C2 pedicle screws have twice the pullout strength of C2 pars screws after cyclical loading. In cases in which the anatomy limits placement of bilateral C2 pedicle screws, a construct using a unilateral C2 pedicle screw with a contralateral short pars screw is a viable option and compares favorably with a bilateral C2 pedicle screw construct.

LEVEL OF EVIDENCE

N/A.

Anterior pedicle screw fixation of C2: an anatomic analysis of axis morphology and simulated surgical fixation

STUDY DESIGN

Human cadaveric study measuring the morphology of C2 vertebra, description of anterior placement of pedicle screw with post-fixation computed tomography (CT) analysis.

OBJECTIVE

To assess the potential feasibility and safety anterior placement of C2 pedicle screws.

SUMMARY OF BACKGROUND DATA

Posterior pedicle screw fixation has become an established technique for upper cervical reconstruction. To our knowledge few reports in the previous literature have described the placement of or anatomy related to anteriorly approach C2 pedicle screws.

METHODS

The morphology of 60 human C2 vertebrae was measured directly to assess the size, position, and relative approach angle of the pedicles from an anterior perspective. In an additional 20 cadaveric cervical spines, bilateral 3.5 mm titanium C2 pedicle screws were placed and analyzed for pedicle morphology and placement accuracy with thin cut, 1 mm axial CT.

RESULTS

The mean C2 pedicle width measured directly and by CT scan was 7.8 and 6.6 mm, and the average length of the right and left pedicle was 26.4 and 25 mm, respectively. The mean transverse angle (α) was 17.6° and 21.4°, whereas declination angle (β) anterior to posterior was 13.8° and 10.6°, respectively.

CONCLUSIONS

Quantitative data regarding C2 pedicle shape and location with respect to the anterior placement of pedicle screws have not been previously reported. This study indicates that anterior placement of 3.5 mm C2 pedicle screws through a transoral approach may be both feasible and safe and also provides an important anatomic analysis that may guide clinical application.

Feasibility of atlantoaxial pedicle screws' placement in children 6-8 years of age: a cadaveric and tomographic study

The aims of this study were to evaluate the linear and angular dimensions of children's atlantoaxial pedicle using cadavers combined with axial computed tomography (CT) and to examine the feasibility of placing atlantoaxial pedicle screws (3.5 mm diameter) on the vertebrae of children 6-8 years of age. Fourteen cadaveric specimens, ranging in age from 6 to 8 years, were dissected to obtain their atlantoaxial vertebrae. We manually measured 12 linear anatomic parameters related to the atlantoaxial pedicle, its lateral mass, and the posterior arch under the vertebral artery groove. CT axial scanning of the atlantoaxial region was performed on 32 healthy children ranging in age from 6 to 8 years. The length of the atlantoaxial pedicles and the angle between the pedicle axis and the midline of the vertebral body were measured on the atlantoaxial transverse CT imaging. It is feasible to place a 3.5 mm screw in the atlantoaxial pedicle of children ranging in age from 6 to 8 years when the appropriate entry point and trajectory of the screw are chosen.

Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws

BACKGROUND CONTEXT

To our knowledge, no large series comparing the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.

PURPOSE

To compare the risk of vertebral artery injury by C1-C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.

STUDY DESIGN

Radiographic analysis using CT scans.

PATIENT SAMPLE

Computed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.

OUTCOME MEASURES

Cortical perforation into the vertebral artery groove of C2 by a screw.

METHODS

We simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤ 5 mm or internal height ≤ 2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤ 4 mm on axial images).

RESULTS

There were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).

CONCLUSIONS

Overall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.

Anterior C3 corpectomy and fusion for complex Hangman's fractures

PURPOSE

The aim of this study was to assess the effectiveness and feasibility of anterior C3 corpectomy and fusion with screw-plate fixation of C2-4 for the treatment of Hangman's fracture in which spinal cord compression comes from the posterosuperior part of C3 vertebral body and the intervertebral disc injury at the C2-3 level.

METHODS

From August 2000 to December 2005, 11 patients (eight males and three females) with traumatic spondylolisthesis of the axis underwent the above surgery. Neurological status was evaluated by the Japanese Orthopaedic Association Score (JOA score). The fusion of the graft, healing of the fracture, and range of motion of the whole cervical spine were examined according to X-ray imaging.

RESULTS

No patient received blood transfusion. There was no deterioration of the neurological function in any case postoperatively. The mean JOA score was significantly improved from 9.1 ± 2.3 preoperatively to 14.8 ± 1.2 at the 12-month postoperative visit. All patients were relieved of axial pain. Imaging evaluation confirmed a high fusion rate and healing rate in all patients. No patient complained of limited mobility of the cervical spine in flexion, extension and rotation. No graft or plate-related complication was observed in any patients during the whole follow-up period. The only postoperative complication was trouble in swallowing liquids in two cases which resolved three months after surgery without any treatment.

CONCLUSIONS

Anterior C3 corpectomy and fusion may prove to be safe and applicable for the treatment of complex Hangman's fractures.

Axis instrumentation: surgical results

OBJECTIVE: Evaluate the surgical results of axis screw instrumentation. METHODS: Retrospective evaluation of the clinical and radiological data of patients submitted to axis fixation using screws. RESULTS: Seventeen patients were surgically treated. The mean age was 41.8 years (range: 12-73). Spinal cord trauma was the most common cause of instability (8 patients - 47%). Bilateral axis fixation was performed in all cases, except one, with laminar screw (total of 33 axis screws). Seven patients (41.1%) underwent bilateral pars screws; laminar screws were used in six cases and pedicular screws were used in two. In two cases, we performed a hybrid construction (laminar + pars and pedicle + pars). There was no neurological worsening or death, nor complications directly related to use axis screws. CONCLUSION: Axis instrumentation was effective and safe, regardless of the technique used for stabilization. Based on our learnt experience, we proposed an algorithm to choose the best technique for axis screw fixation.

Comparison of safety and stability of C-2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review of the literature

OBJECT

Some centers report a lower incidence of vertebral artery (VA) injury with C-2 pars screws compared with pedicle screws without sacrificing construct stability, despite biomechanical studies suggesting greater load failures with C-2 pedicle screws. The authors reviewed published series describing C-2 pars and pedicle screw implantation and atlantoaxial fusions and compared the incidence of VA injury, screw malposition, and successful atlantoaxial fusion with each screw type.

METHODS

Online databases were searched for English-language articles between 1994 and April of 2011 describing the clinical and radiographic outcomes following posterior atlantoaxial fusion with C-1 lateral mass and either C-2 pars interarticularis or pedicle screws. Thirty-three studies describing 2975 C-2 pedicle screws and 11 studies describing 405 C-2 pars screws met inclusion criteria for the safety analysis. Seven studies describing 113 patients treated with C-2 pars screws and 20 studies describing 918 patients treated with C-2 pedicle screws met inclusion criteria for fusion analysis. Standard and formal meta-analysis techniques were used to compare outcomes.

RESULTS

All studies provided Class III evidence. Ten instances of VA injury occurred with C-2 pedicle screws (0.3%) and no VA injury occurred with pars screws. The point estimate of VA injury for C-2 pedicle screws was 1.09% (95% CI 0.73%-1.63%) and was similar to that of C-2 pars screws (1.48%, 95% CI 0.62%-3.52%). Similarly, there was no statistically significant difference in the rate of clinically significant screw malpositions (1.14% [95% CI 0.77%-1.69%) vs 1.69% [95% CI 0.73%-3.84%]). Radiographically identified screw malposition occurred in a higher proportion of C-2 pedicle screws compared with C-2 pars screws (6.0% [95% CI 3.7%-9.6%] vs 4.0% [95% CI 2.0%-7.6%], p < 0.0001). Pseudarthrosis occurred in a greater proportion of patients treated with C-2 pars screws (5 [4.4%] of 113) compared with those treated with C-2 pedicle screws (2 [0.22%] of 900). Point estimates with 95% confidence intervals show a slightly higher rate of successful atlantoaxial fusion in the pedicle screw cohort (97.8% [CI 96.0%-98.8%] vs 93.5% [CI 86.6%-97.0%]; p < 0.0001). Q-testing ruled out heterogeneity between the study groups.

CONCLUSIONS

With a thorough knowledge of axis anatomy, surgeons can place both C-2 pars and C-2 pedicle screws accurately with a small risk of VA injury or clinically significant malposition. There may be subtle trade-off of safety for rigidity when using axial pedicle instead of pars screws, and the decision to use either screw type must be made only after careful review of the preoperative CT imaging and must take into account the surgeon's expertise and the particular demands of the clinical scenario in any given case.

A clinical morphologic study of the C2 pedicle and isthmus

PURPOSE

This anatomic, radiographic study investigated locational differences in the C2 pedicle and isthmus [pediculoisthmic component (PIC)] and characterized its narrowest section for clinical application in posterior C2 screw fixation.

METHODS

Structures surrounding the transverse foramina of 30 dry C2s and 10 C3s were compared morphologically. Spinal CT scans of 32 Chinese adults were subjected to volume rendering and multiplanar reconstruction to identify the narrowest C2 PIC, and correlative parameters were measured and analyzed.

RESULTS

Inferior C2 and C3 structures were morphologically similar. In superior view, the C2 superior facets lay on the transverse foramen and the upper portion between superior and inferior facets was flat (average mediolateral angle, 11.1° ± 2.4°). In inferior view, the posteroinferomedial portion of the C2 transverse foramen displayed a partially tubular structure (average mediolateral angle of projection, 42.6° ± 4.9°). Average height and width were 11.6 and 6.9 mm. The inner medullary cavity was elliptical and the middle site of endosteal diameter was 3.3 ± 1.9 mm. Medial internal cortical bone was significantly thicker than lateral bone (P < 0.01).

CONCLUSIONS

The PIC is located between superior and inferior C2 facets. The superior flat area is the isthmus and the inferomedial area connecting the inferior facet and vertebral body is the pedicle. The pedicle is partially tubular and projects posteromedially to the transverse foramen. The narrowest PIC section is the narrowest point of the C2 pedicle. Considering its thin lateral cortical bone, medial and superior pedicle screw placement and preoperative CT reconstruction are recommended.

Accuracy of the freehand technique for 3 fixation methods in the C-2 vertebrae

Object

Intraoperative imaging often does not provide adequate visualization to ensure safe placement of screws. Therefore, the authors investigated the accuracy of a freehand technique for placement of pars, pedicle, and intralaminar screws in C-2.

Methods

Sixteen cadaveric specimens were instrumented freehand by 2 experienced cervical spine surgeons with either a pars or pedicle screw, and bilateral intralaminar screws. The technique was based on anatomical starting points and published screw trajectories. A pedicle finder was used to establish the trajectory, followed by tapping, palpation, and screw placement. After placement of all screws (16 pars screws, 16 pedicle screws, and 32 intralaminar screws), the C-2 segments were disarticulated, radiographed in anteroposterior, lateral, and axial planes, and meticulously inspected by another spine surgeon to determine the nature and presence of any defects.

Results

A total of 64 screws were evaluated in this study. Pars screws exhibited 2 critical defects (1 in the foramen transversarium and 1 in the C2–3 facet) and an insignificant dorsal cortex breech, for an overall accuracy rate of 81.3%. Pedicle screws demonstrated only 1 insignificant violation (inferior facet/medial cortex intrusion of 1 mm) with an accuracy rate of 93.8%, and intralaminar screws demonstrated 3 insignificant violations (2 in the ventral canal, 1 in the caudad lamina breech) for an accuracy rate of 90.6%. Pars screws had significantly more critical violations than intralaminar screws (p = 0.041).

Conclusions

Instrumentation of the C-2 vertebrae using the freehand technique for insertion of pedicle and intralaminar screws showed a high success rate with no critical violations. Pars screw insertion was not as reliable, with 2 critical violations from a total of 16 placements. The freehand technique appears to be a safe and reliable method for insertion of C-2 pedicle and intralaminar screws.

Posterior short-segment fixation and fusion in unstable Hangman's fractures

STUDY DESIGN

A retrospective study. OBJECTIVE.: To introduce the method of C2-C3 posterior short-segment fixation and fusion in unstable Hangman's fracture and to evaluate the clinical effects.

SUMMARY OF BACKGROUND DATA

Hangman's fracture can be managed by closed reduction and immobilization. However, surgery is usually preferable in highly unstable cases and in rigid arthrodesis failure. The outcome of surgical treatment for unstable Hangman's fracture has not been thoroughly investigated.

METHODS

Thirty-five patients with unstable Hangman's fracture were treated using C2-C3 posterior short-segment fixation and fusion. Twenty-six cases used C2-C3 short-segment pedicle screw fixation. Nine cases used both C2 pedicle screw and C3 lateral mass screw short-segment fixation and fusion. C-arm fluoroscopy was used for the whole procedure. RESULTS.: All patients were observed for an average of 44 months, ranging from 12 to 78 months. There was no screw loosening or breakage, nor was there any spinal cord or vertebral artery injury intraoperatively. A total of 140 screws were placed, with 70 screws inserted into the C2 pedicle, 52 into the C3 pedicle, and 18 into the C3 lateral mass. Computed tomography scans indicated 9 screws were placed too close to the vertebral artery canal in C2, and 12 screws were too close to the canal in the C3 pedicle, all without clinical consequences. C3 lateral mass screws were placed successfully. Neurologic status improved from C and D to E in all 8 cases. Static and dynamic films demonstrated that fusion was achieved in all cases 6 months after surgery. No graft or plate-related complications were observed in any patients during the entire follow-up period.

CONCLUSION

C2-C3 posterior short-segment fixation and fusion is an effective method for the management of unstable Hangman's fracture, proving its value as a technique for achieving solid bony fusion combined with a low rate of complications.

Direct posterior reduction and fixation for the treatment of basilar invagination with atlantoaxial dislocation

OBJECTIVE

To report the surgical technique and clinical results for the treatment of basilar invagination (BI) with atlantoaxial dislocation (AAD) by direct posterior reduction and fixation using intraoperative distraction between the occiput and C2 pedicle screws.

METHODS

From May 2004 to June 2008, 29 patients who had BI with AAD were surgically treated in our department. Pre- and postoperative dynamic cervical x-rays, computed tomographic scans, and 3-dimensional reconstruction views were performed to assess the degree of dislocation. Ventral compression of the cervicomedullary junction was evaluated by magnetic resonance imaging. For all patients, reduction of the AAD was conducted by intraoperative distraction between the occiput and C2 pedicle screws using a direct posterior approach.

RESULTS

Follow-up ranged from 6 to 50 months in 28 patients. Clinical symptoms improved in 26 patients (92.9%) and were stable in 2 patients (7.1%) without postoperative deterioration. Radiologically, complete or more than 50% reduction was achieved in 27 of 28 patients (96.4%). In 1 patient, the reduction was less than 50% because the direction of the facets on 1 side of the C1-C2 joint was vertically oriented, instead of horizontal. Overall, good decompression and bone fusion were shown on postoperative magnetic resonance imaging, computed tomography, or x-ray scans for all patients. There was 1 death in the series because of basilar artery thrombosis 1 week after the operation.

CONCLUSION

The direct posterior distraction technique between occiput and C2 pedicle screws is an effective, simple, fast, and safe method for the treatment of BI with AAD. Transoral odontoidectomy and cervical traction for the treatment of BI with AAD should be reconsidered.

A radiographic computed tomography–based study to determine the ideal entry point, trajectory, and length for safe fixation using C-2 pars interarticularis screws

Object

Effective methods for fixation of the axis include C1–2 transarticular and C-2 pedicle screw placement. Both techniques pose a risk of vertebral artery (VA) injury in patients with narrow pedicles or an enlarged, high-riding VA. Pars screws at C-2 avoid the pedicle, but can cause VA injury with excessively long screws. Therefore, the authors evaluated various entry points and trajectories to determine ideal pars screw lengths that avoid breaching the transverse foramen.

Methods

Both pars were studied on 50 CT scans (100 total). Various pars lengths were assessed using 2 entry points and 3 trajectories (6 measurements). Entry point A was the superior one-fourth of the lateral mass. Entry point B was 3-mm rostral to the inferior aspect of the lateral mass. Using entry points A and B, Trajectory 1 was the minimum distance to the transverse foramen; Trajectory 2 was the maximum distance to the transverse foramen; and Trajectory 3 was the steepest angle to the pars/C-2 superior facet junction without transverse foramen breach.

Results

The mean patient age was 46 ± 17 years, and 84% of the CT scans reviewed were obtained in men. There was no significant difference in right or left measurements. Entry point B demonstrated greater pars lengths for each trajectory compared with entry point A (p < 0.0001). For both entry points, Trajectory 3 provided the greatest pars length. Using Trajectory 3 with entry point B, 84, 95, and 99% had a pars length that measured ≥ 18, 16, and 14 mm, respectively. Using Trajectory 3 with Entry point A, only 41, 64, and 87% had a pars length that measured ≥ 18, 16, and 14 mm, respectively.

Conclusions

Using an entry point 3-mm rostral to the inferior edge of the lateral mass and a trajectory directed toward the superior facet/pars junction, 99% of partes interarticularis in this study would tolerate a 14-mm screw without breach of the transverse foramen.

Minimally Invasive Atlantoaxial Fusion

BACKGROUND

C1–C2 fusion has significantly advanced from predominantly wiring/cable modalities to more biomechanically stable screw-rod techniques. Minimally invasive surgical techniques represents the most recent modification of atlantoaxial fixation. The indications, rationale, and surgical technique of this novel procedure are described.

METHODS

Six patients requiring C1–C2 fusion (5 type II odontoid fractures and 1 os odontoideum) underwent minimally invasive C1–C2 fusion over a 2-year period. The cohort consisted of 5 men and 1 woman with a mean age of 51 years (age range, 39–64 y). All 6 patients underwent bilateral segmental atlantoaxial fixation using an expandable tubular retractor.

RESULTS

The mean follow-up time was 32 months (age range, 24–46 mo) There were no intraoperative complications, and the mean estimated blood loss was 100 mL. Solid fusion was achieved in all 6 patients, without pathological motion on dynamic studies. Postoperative computed tomographic images showed no hardware malposition in the scanned patients (4 of the 6 patients).

CONCLUSIONS

Placement of C1 and C2 instrumentation using minimally invasive techniques is technically feasible. Because the instrumentation and the means of obtaining arthrodesis do not differ substantively from the standard approach, we would not anticipate long-term results to be different from those of an open procedure, apart from the approach-related morbidity.

Anatomic considerations for C2 pedicle screw placement: the use of computerized tomography measurements

OBJECTIVE: more detailed anatomical knowledge of the C2 pedicle is required to optimize and minimize the risk of screw placement. The aim of this study was to evaluate the linear and angular dimensions of the true C2 pedicle using axial CT. METHODS: ninety three patients (47 males, 46 females mean age 48 years) who had cervical spinal CT imaging performed were evaluated for this study. Axial images of the C2 pedicle were selected and the following pedicle parameters were determined: pedicle width (PW, the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis) and pedicle transverse angle (PTA, that is, the angle between the pedicle axis and the midline of the vertebral body). RESULTS: the overall mean pedicle width was 5.8 1.2mm. The mean pedicle width in males (6.01.3mm) was greater than that in the female subjects (5.6 1.1mm). This difference was not found to be statistically significant (p=.6790). The overall mean pedicle transverse angle was 43.93.9 degrees. The mean PTA in males was 43.23.8 degrees, while that in females was 44.73.7 degrees. CONCLUSION: preoperative planning is absolutely mandatory, particularly in determining not only screw trajectory, but in analyzing individual patient anatomy and reception to a C2 pedicle screw.

The cervical end of an occipitocervical fusion: a biomechanical evaluation of 3 constructs. Laboratory investigation

OBJECT

Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link.

METHODS

Ten intact human cadaveric spines (Oc-C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested.

RESULTS

All constructs demonstrated a significant increase in stiffness after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct.

CONCLUSIONS

All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.

Fusions at the craniovertebral junction

INTRODUCTION

The surgical management of craniovertebral junction instability in pediatric patients has unique challenges. While the indications for internal fixation in children are similar to those of adults, the data concerning techniques, complications, and outcomes of spinal instrumentation comes from experience with adult patients. Diminutive osseous and ligamentous structures and anatomical variations associated with syndromic craniovertebral abnormalities frequently complicates the approaches and limits the use of internal fixation in children. Cervical arthrodesis in the pediatric age group has the potential for limiting growth potential and causing secondary deformity. Recent advances in image analysis have enabled preoperative planning which is critical to evaluate the size of instrumentation and its relation to the patient's anatomy. Newer techniques have recently evolved and have been incorporated in the management of pediatric patients with requirement for craniocervical stabilization.

MATERIALS AND METHODS

Over 750 craniovertebral junction fusions have been reviewed in children. The indications for atlantoaxial arthrodesis were: (a) absent odontoid process, dystopic os odontoideum, absent posterior arch of C1; (b) Morquio's syndrome, Goldenhar's syndrome, Conradi's syndrome, and spondyloepiphyseal dysplasia. The acquired abnormalities of trauma, postinfectious instability, and Down's syndrome completed the indication in children. The indications for occipitocervical fusion were: (a) anterior and posterior bifid C1 arches with instability, absent occipital condyles; b) severe reducible basilar invagination, unstable dystopic os odontoideum, and unilateral atlas assimilation; (c) acquired phenomenon with traumatic occipitocervical dislocation, complex craniovertebral junction fractures of C1 and C2, after transoral craniovertebral junction decompression, cranial settling in Down's syndrome and inflammatory disease such as Grisel's syndrome. Instability was seen in children with clivus chordoma and osteoblastoma. Atlantoaxial fusions were performed mainly with interlaminar rib graft fusion and more recently with the transarticular screw fixation in the older patient. In the teenager, lateral mass screws at C1 and rod fixation were made; C2 pars interarticular screw fixation and C2 pedicle screw fixation. A C2 translaminar screw fixation is described. Occipitocervical fusions were made utilizing rib grafts below the age of 6. A contoured loop fixation was made in children above the age of 7, and recently, rod and screw fixation was also utilized.

RESULTS

Abnormal cervical spine growth was not seen in children who underwent craniocervical stabilization below the age of 5. The authors have reserved rigid instrumentation for children above the age of 10 years and dependent on the anatomy.

Rheumatoid arthritis as a risk factor for a narrow C-2 pedicle: 3D analysis of the C-2 pedicle screw trajectory

Object

Vertebral artery (VA) injury is a potentially serious complication of C-2 pedicle screw (PS) fixation. Although this surgery is frequently performed in patients with rheumatoid arthritis (RA), few studies have compared the risk of VA injury in patients with and without RA. In this study, the authors compare the morphological risk of VA injury relating to C-2 PS fixation in patients with and without RA.

Methods

A total of 110 3D CT images of the cervical spine including the axis were evaluated. Fifty patients with RA and 60 patients without RA were included in the study. The maximum PS diameter (MPSD) that could be used at C-2 without breaching the cortex was measured in 3D using a computer-assisted navigation system. A narrow-pedicle carrier was defined as a patient with an MPSD of 4 mm or less.

Results

In the RA group, 42 of 100 MPSDs were ≤ 4 mm, and 30 of 50 patients (60%) were narrow-pedicle carriers. In the non-RA group, 10 of 120 MPSDs (8%) were ≤ 4 mm, and 8 of 60 (13%) patients were narrow-pedicle carriers. The MPSD, the anteroposterior (AP) diameter of C-3, and the ratio of MPSD to the AP diameter of C-3 were significantly smaller in the RA group than in the non-RA group. Multiple logistic regression analysis showed that RA and narrow C-3 AP diameter were significant risk factors for a narrow-pedicle carrier.

Conclusions

Rheumatoid arthritis is a significant risk factor for a narrow C-2 pedicle. When performing PS placement at C-2, particularly in patients with RA, thorough preoperative evaluation of the bone architecture is very important for avoiding inadvertent injury to the VA.

The feasibility of microscope-assisted "free-hand" C1 lateral mass screw insertion without fluoroscopy

STUDY DESIGN

Retrospective study.

OBJECTIVE

To determine if C1 lateral mass screws could be safely inserted without the use of fluoroscopy.

SUMMARY OF BACKGROUND DATA

Standard surgical technique for C1 lateral mass screw placement uses intraoperative fluoroscopy. However, intraoperative fluoroscopy is time consuming, cumbersome, and exposes both the patient and surgical team to radiation.

METHODS

Radiographic analysis and chart review. Surgical technique was analyzed in 3 components: feasibility to complete the screw insertion without intraoperative fluoroscopic guidance; occurrence of any intraoperative, perioperative complications; and radiologic assessment of screw positions on roentgenogram.

RESULTS

Forty-six C1 lateral mass screws were inserted in 24 consecutive patients who underwent posterior cervical fusion. There were 19 female and 5 male. The mean age was 63 +/- 18 years at the time of surgery. All C1 lateral mass screws were inserted unicortically using a microscope-assisted "free-hand" technique. The average intraoperative blood loss in C1-C2 fusion was 123 +/- 50 mL. The mean operative time for each C1-C2 fusion was 133 +/- 30 minutes. Satisfactory positions of C1 screws were noted in intraoperative and postoperative radiograph examinations. There was no mortality or wound infection. There was no cortical breach along the screw path palpated intraoperatively. No vertebral artery injury or cerebral spinal fluid leakage during the screw insertion was observed. However, one patient with a prior posterior cervical operation had a dural tear during the exposure, another had new occipital neuralgia, and a third patient had a symptomatic occipitocervical joint violation by a C1 screw, which was diagnosed only on computed tomography scans. The symptoms resolved after the C1 screws were removed.

CONCLUSIONS

Microscope-assisted "free-hand" C1 lateral mass screws insertion is a feasible and reproducible technique. which offers an alternative method of screw insertion without cumbersome and potentially harmful fluoroscopy.

Cervical spine trauma in the pediatric patient

Injuries to the pediatric cervical spine occur infrequently. Numerous unique anatomic and biomechanical features of the pediatric spine render it much more flexible than the adult spine. These features give rise to significant differences in the presentation, diagnosis, treatment, and prognosis of pediatric cervical trauma compared with adults. Younger children more often suffer injury to the upper cervical spine with greater neurologic injury and fewer fractures. Once the child reaches the age of 10 years, he or she develops a more adult-type spine, and injuries are thus more similar to those seen in the adult population. The unique anatomic and biomechanical differences in the pediatric spine are discussed, along with the various common and unique injuries.

Safety and efficacy of C2 pedicle screws placed with anatomic and lateral C-arm guidance

STUDY DESIGN

This is a retrospective review of 150 C2 pedicle screw placements. Candidates had their C2 pedicle morphology assessed through three-dimensional imaging, including preoperative image guidance. After surgery, the patients were serially CT scanned. Follow-up, with fusion assessment, ranged from 1 to 12 years.

OBJECTIVE

We will show that an open technique combined with lateral C-arm guidance provides rapid placement of C2 pedicle screws.

SUMMARY OF BACKGROUND DATA

C2 pedicle screws can be successful anchors for a variety of cervical problems. Standard intraoperative image guidance, biplane fluoroscopy, or free hand techniques all have their drawbacks.

METHODS

After adequate C2 exposure, the C2 pedicle is palpated. The dissector remains stationary to provide coronal orientation while a lateral C-arm radiograph is obtained for sagittal orientation. The drill trajectory is set, the C2 pedicle cannulated, and a cancellous screw placed.

RESULTS

A total of 71 patients had bilateral screws placed and 8 patients had unilateral screws placed. The overall complication rate was 2.7%.

CONCLUSIONS

In our series, we have found a consistent way to cannulate the C2 pedicle. C2 fixation serves as an integral part of cervical reconstruction. Preoperative planning, anatomic knowledge, and lateral C-arm orientation create a low morbidity method for C2 screw placement.

The borders of the odontoid process of C2 in adults and in children including the estimation of odontoid/body ratio

The odontoid process of C2 projects upward from the superior roof of the body of C2. There is a confusion about the inferior border of the odontoid. The aims of this clinical study were to describe the inferior border of the odontoid process based on the remnant of dentocentral synchondrosis in adults, and the estimation of the odontoid/body ratio in pediatric and adult ages. Sixty-six cases were included for this study. Forty-four of them were in adult ages and the remaining 22 of them were in pediatric ages. The region of occiput, C1, C2, and C3, was examined with the magnetic resonance imaging (MRI) in all cases. The length of the odontoid process was estimated by using radiological images of MR from the tip of the odontoid to the remnant of dentocentral synchondrosis. The portion located under the level of synchondrosis was considered as the body of C2. The average length of the odontoid was 18. 6 mm in pediatric and 21. 3 mm in adult cases. In adult females, the length of the odontoid process (19. 1 mm in length) was smaller than those of adult males (23. 6 mm in length). The average ratio of odontoid/body was two in pediatric and 1.8 in adult cases. This study demonstrated that the neck of the odontoid segment at the level of superior articulating facets is not the synchondrosis between the odontoid process and the body of C2. The synchondrosis is located well below the level of superior articulating facets. It can be demonstrated with sagittal and coronal images of MR in both of pediatric and adult individuals.

Pedicle fracture of the axis: report of two cases and a review of literature

Clinical and neuroradiological features of two cases with unilateral pedicle fractures of C2 were presented and the literature of this rare traumatic fracture was reviewed. Both 37- and 57-year-old woman had traffic accident and were admitted in our institute. Both patients were neurologically free except for neck pain. Plain X-ray of cervical spine did not show abnormal findings. Computerized tomography (CT) with bone window showed the location and extension of the traumatic fracture in C2 pedicle. The fracture was located in the portion between the lateral border of the odontoid process and pars interarticularis. Fractures of the C2 pedicle are rarely seen in acute traumatic fractures. They can be overlooked because there is confusion in the describing of anatomical location of C2 pedicle in some medical literature. For proper diagnosis of pedicle fracture of the axis, understanding of the anatomy of C2 and CT findings with bone window are important.

An anatomical study of the C-2 pedicle

Object. The C-2 pedicle plays an important role regarding screw purchase for spinal fixation. The aim of this study was to measure the C-2 pedicle—related linear and angular parameters.

Methods. Seven parameters in 160 C-2 pedicles (80 dry vertebrae) were measured using a Vernier caliper (accurate to 0.1 mm) and goniometer. The Student t-test was used to determine statistical significance.

The authors found that the C-2 isthmus (pars interarticularis) and the C-2 pedicle are distinct structures. The C-2 isthmus covers the pedicle. The isthmus is present between the superior and inferior articular processes, and the pedicle is the structure beneath the C-2 isthmus. It connects the lateral mass—inferior articular process to the body of the axis. The heights of the right and the left C-2 pediculoisthmic components (PICs) were 10.3 ± 1.6 and 9.9 ± 1.5 mm, respectively. The posterior part of the superior aspect of the PIC was wider than the anterior portion. The widths of the posterosuperior aspect of the PIC were 11.1 ± 2 and 11 ± 1.7 mm on the right and left sides, whereas the widths of the anterosuperior aspect of the PIC were 7.9 ± 1.7 and 8.5 ± 1.6 mm, respectively. The inferior widths of this component were 6.0 ± 1.5 and 5.5 ± 1.3 mm on the right and left side, respectively. The lengths of the component were 28.8 ± 2.9 mm on the right and 28.8 ± 3.4 mm on the left side. The PIC exhibits a lateral-to-medial and an inferior-to-superior angle. Its axial angles were 28.4 ± 2.5 and 28.6 ± 2.2° on the right and left sides, respectively; its sagittal angles were 18.8 ± 2.1 and 18.8 ± 1.7°, respectively.

Conclusions. The C-2 pedicle can be seen in the inferior aspect of the vertebra, and it connects posterior vertebral elements (that is, the lateral mass and inferior articular process) to the axial body. The isthmus drapes the pedicle. The authors suggest that this be termed “the pediculoisthmic component.”

Posterior atlantoaxial stabilization: new alternative to C1–2 transarticular screws

Object

Surgical treatment of atlantoaxial instability has evolved to include various posterior wiring techniques including Brooks, Gallie, and Sonntag fusions in which success rates range from 60 to 100%. The Magerl–Seemans technique in which C1–2 transarticular screws are placed results in fusion rates between 87 and 100%. This procedure is technically demanding and requires precise knowledge of the course of the vertebral arteries (VAs). The authors introduce a new C1–2 fixation procedure in which C-1 lateral mass and C-2 pedicle screws are placed that may have advantages over C1–2 transarticular screw constructs.

Methods

A standard posterior C1–2 exposure is obtained. Polyaxial C-2 pedicle screws and C-1 lateral mass screws are placed bilaterally. Rods are connected to the screws and secured using locking nuts. A cross-link is then placed. Fusion can be performed at the atlantoaxial joint by elevating the C-2 nerve root.

The technique for this procedure has been used in four cases of atlantoaxial instability at the author's institution. There have been no C-2 nerve root– or VA-related injuries. No cases of construct failure have been observed in the short-term follow up period.

Conclusions

Atlantoaxial lateral mass and axial pedicle screw fixation offers an alternative means of achieving atlantoaxial fusion. The technique is less demanding than that required for transarticular screw placement and may avoid the potential complication of VA injury. The cross-linked construct is theoretically stable in flexion, extension, and rotation. Laminectomy or fracture of the posterior elements does not preclude use of this fixation procedure.