BACKGROUND: Neck pain and headaches can arise from the lateral atlanto-axial joint (LAA joint). This pain can be diagnosed with intra-articular injections of local anesthetic. A widely used technique for access to the lateral atlanto-axial joint uses a posterior approach, but this approach can be hazardous because of the proximity of the vertebral artery, the dural sac, and the C2 spinal nerve and dorsal root ganglion.
OBJECTIVE: The objective was to describe and test a new technique for accessing the LAA joint that avoids structures that lie behind the joint.
METHODS: The new technique was described, and tested for tolerance in 10 patients with unilateral suboccipital pain, and tenderness over the LAA joint, along with evidence of LAA joint arthropathy on SPECT CT. The technique requires inserting a needle along a trajectory tangential to the dorsal surface of the C2 lamina. It involves obtaining a declined view of the C2 lamina and C2 pedicle.
CONCLUSIONS: In all cases, the C2 pedicle was easily identified and allowed the needle to pass asymptomatically underneath the neurovascular structures behind the joint. The tactile response of the lamina of C2 provided important feedback regarding needle depth caudal to the LAA joint.

To radiologically examine the pedicle, lamina, and vertebral artery foraminal anatomies at the C2 vertebra for pedicular and laminar screw instrumentation at the axis in a Turkish population.
From 2018 to 2019, we evaluated 100 patients who underwent cervical computed tomography (CT) for various reasons (excluding cervical pathologies) at Marmara University Hospital. The C2 pedicles were measured on CT images using measurement tools. In addition, axial computed tomography was performed at 0.1 mm intervals. Bilateral measurements were performed for each case.
The median right and left pedicle axial diameters were 5.01 and 5.09 mm, respectively for the male patients and 4.31 and 4.38 mm for the female patients, showing a statistically significant difference between the sexes (P < 0.01). Of the patients, 15% had narrow pedicles. The pedicle sagittal diameters were smaller than 5 mm in 30% of the computed tomographic series. The internal height was <2 mm in 4% of the cases.
Our findings suggest significant individual and sex-related differences. Vertebral artery groove anomalies are commonly observed. Before performing a posterior craniocervical instrumentation surgery, a computed tomography (CT) examination is beneficial because high-riding vertebral arteries must be kept in mind in determining the appropriate screw diameter and screw trajectory.

To evaluate and describe the morphologic features of the C2 pedicle in patients with basilar invagination (BI) for informing the placement of pedicle screws. C2 pedicle screw placement is an important surgical technique for the treatment of atlantoaxial instability in patients with BI. However, no systematic and comprehensive anatomical study of the C2 pedicle in patients with BI has been reported.
The data from 100 patients diagnosed with BI (BI group) and 100 patients without head or cervical disease (control group) were included in the study. Radiographic parameters, including the pedicle width, length, height, transverse angle, lamina angle, and superior angle, were measured and analyzed on CT images. After summary analysis, the effect of C2-3 congenital fusion on C2 pedicle deformity in patients with BI was also investigated.
The width, length, and height of the C2 pedicle of the BI patients were smaller than those of the control group. The pedicle cancellous bone was smaller in the BI group, while no significant difference in cortical bone was observed. In total, 44% of the pedicles were smaller than 4.5 mm in the BI group. Patients with C2-3 congenital fusion presented with smaller pedicle transverse angles and larger pedicle superior angles than those without fusion. Wide variations in the left and right angles of the pedicle were observed in the BI group with atlantoaxial dislocation or atlantooccipital fusion.
The C2 pedicle in the BI group was thinner than that in the control group due to a smaller cortical bone. Cases of C2-3 congenital fusion, atlantoaxial dislocation, and atlantooccipital fusion displayed variation in the angle of the C2 pedicle.

UNASSIGNED: Atlantoaxial Dislocation (AAD) is a complex disorder of craniovertebral junction (CVJ). Many techniques are available to treat AAD but there are some specific conditions where some techniques have advantage over the other.
UNASSIGNED: C2-3 transfacetal screw with standard C1 lateral mass fixation provides a stronger construct because of four cortices incorporation and divergent course of screws and is biomechanically comparable to other forms of C2 fixation techniques. It is a technically less demanding and time-consuming. It is also a good alternative in cases having significant osteopenia.
UNASSIGNED: C2-3 transfacetal screw with standard C1 lateral mass fixation is an effective alternative to routine C1 lateral mass and C2 pedicle/pars screw fixation in cases of atlantoaxial dislocation complicated with high riding or posteriorly placed vertebral artery and thin pedicle of C2 vertebra.

We retrospectively analyzed atlantoaxial dislocation (AAD) of various pathologies, namely, rheumatoid arthritis (RA), os odontoideum, and trauma. Various techniques were discussed in relation to C1-C2 stabilization. The study aims to share our clinical experience in a series of six cases of C1-C2 instability that underwent posterior C1-C2 fusion, with free hand technique and limited fluoroscopy. The clinicoradiological presentation for each patient is described. We reviewed different literatures related to our case vividly and focused on the basic neuroanatomy involved in the atlantoaxial joint. All patients of AAD had evidence of severe canal compromise and chronic compressive spinal cord changes. In our study, the patients age ranged from 28 to 52 years. The study included four males and two females. Out of six patients of AAD, three had history of trauma, two had os odontoideum, and one had chronic inflammatory condition (RA). From our case series, we concluded that the Goel-Harms technique is the most versatile and surgeon friendly technique for C1-C2 fixation. Early recognition and surgical intervention of atlantoaxial joint instability is essential to prevent catastrophic neurological complications.

The preoperative assessment of C2 morphology is important for safe instrumentation. Sclerotic changes are often seen in C2 pedicles. Evaluating the diameter measurements solely might not accurately assess the safety of screw insertion. We have proposed a novel grading system of the C2 pedicle that includes sclerosis and evaluated the predictive value of this grading system with the surgeon\'s safety evaluation.
We reviewed and measured the dimensional values in 220 cervical computed tomography angiograms. Additionally, we used a grading system that divides the findings into 5 grades according to the width measurement and degree of sclerosis in the C2 pedicle. Two spine surgeons independently classified the pedicles as follows: safe (minimal risk of pedicle violation), caution needed (caution to minimize pedicle violation), or dangerous (a high risk of pedicle violation). Finally, we compared the measurements and the surgeons\' safety assessments.
A total of 411 pedicles of 203 patients (mean age, 69.5 years; 49.5% women) were included. Of the 411 C2 pedicles, 170 were classified as high risk by ≥1 surgeon. Between the dimensional measurements and grading system, the sclerotic grade showed the best predictive value.
We have introduced a novel tool to evaluate the safety of C2 pedicle screw placement. Our results suggest that our pedicle width-sclerosis grading system is reproducible and predicts the surgeon\'s assessment of safe screw placement better than C2 pedicle diametrical measurements alone.

METHODS: Systematic review and meta-analysis.
OBJECTIVE: The purpose of this study was to compare the safety and accuracy of the C2 pedicle versus C2 pars screws placement and free-hand technique versus navigation for upper cervical fusion patients.
METHODS: Databases searched included PubMed, Scopus, Web of Science, and Cochrane Library to identify all papers published up to April 2020 that have evaluated C2 pedicle/pars screws placement accuracy. Two authors individually screened the literature according to the inclusion and exclusion criteria. The accuracy rates associated with C2 pedicle/pars were extracted. The pooled accuracy rate estimated was performed by the CMA software. A funnel plot based on accuracy rate estimate was used to evaluate publication bias.
RESULTS: From 1123 potentially relevant studies, 142 full-text publications were screened. We analyzed data from 79 studies involving 4431 patients with 6026 C2 pedicle or pars screw placement. We used the Newcastle-Ottawa Scale (NOS) to evaluate the quality of studies included in this review. Overall, funnel plot and Begg\'s test did not indicate obvious publication bias. The pooled analysis reveals that the accuracy rates were 93.8% for C2 pedicle screw free-hand, 93.7% for pars screw free-hand, 92.2% for navigated C2 pedicle screw, and 86.2% for navigated C2 pars screw (all, P value < 0.001). No statistically significant differences were observed between the accuracy of placement C2 pedicle versus C2 pars screws with the free-hand technique and the free-hand C2 pedicle group versus the navigated C2 pedicle group (all, P value > 0.05).
CONCLUSIONS: Overall, there was no difference in the safety and accuracy between the free-hand and navigated techniques. Further well-conducted studies with detailed stratification are needed to complement our findings.

BACKGROUND: Preoperative assessment of C2 pedicle morphology is critical to safe pedicle screw placement. To avoid iatrogenic injury, complex digital templating software has been introduced; however, this technology may not be available in many centers. We report a technique for preoperative assessment of C2 pedicle screw placement safety based upon 2-dimensional sagittal computed tomography (CT) scan images and verify its utility in clinical practice.
METHODS: A total of 46 consecutive patients underwent cervical spine CT scans between 2005 and 2011. The C2 pedicle morphology was assessed on sagittal CT imaging by 5 independent reviewers to determine the feasibility and risk associated with pedicle screw placement. Thirty consecutive patients underwent C2 pedicle screw placement and were followed clinically for a minimum of 2 years. The ability to place a screw was noted, and accuracy of screw placement was assessed postoperatively by CT scan.
RESULTS: The CT scan analysis demonstrated that 11% (5/46) of patients had sufficient pedicle size bilaterally to allow safe placement of long pedicle screws with a low risk of vertebral artery injury, whereas 15% (7/46) were considered a high risk bilaterally. Screw placement was deemed low risk in 28%, moderate risk in 38%, and high risk in 34%. Excellent intraobserver reliability and good interobserver reliability was observed. Clinically, 18 of 20 (90%) low-risk and 21 of 24 (88%) moderate-risk pedicle screws were placed safely versus 5 of 16 (31%) high-risk pedicle screws (P < .001).
CONCLUSIONS: Using the described technique for evaluating the C2 pedicle via sagittal CT scan images allows for safe and reliable pedicle screw placement without relying upon complex digital templating software, which may have limited availability.
METHODS: II.
CONCLUSIONS: This study aids in the surgical decision-making behind the placement of C2 pedicle screws using CT scans without reliance upon complex digital templating software.

BACKGROUND: Screw diameters currently available are based on the literature available. No data are available for the safety margin available for C2 pedicle screw placement. The objective of this study was to define the average pedicle size available for placing C2 pedicle screws and to quantify the safety margin available in case of lateral breach of screw.
METHODS: Computed tomography angiograms of 259 patients (161 men, 98 women) were analyzed to calculate the C2 pedicle width, the area of the transverse foramen (TF) and the vertebral artery (VA), and the occupation ratio (OR) of the VA within the TF. The VA was classified into groups based on its lie within the TF (anteromedial, anterolateral, posteromedial, posterolateral, central, ectatic). The distance which the pedicle screw can breach without encountering the VA was calculated (lateral pedicle to vertebral artery distance [LPVA]). The diameters of the VA and the TF were estimated, and their difference gives the safety margin in case of breach of the lateral cortex of the C2 pedicle.
RESULTS: The mean mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis, in women was 5.3 mm and in men it was 5.8 mm. This difference was statistically significant. In 53.9% (122/226) of patients, the VA was dominant on the left side. The overall mean OR at the C2 vertebral level was found to be 37.3%. The mean LPVA was 0.9 mm, and the average overall safety margin available was 2.5 mm (range, 0.4-5.3 mm).
CONCLUSIONS: This study describes the relationship of the VA in the C2 TF and the relative risk during pedicle screw fixation.

C2 pedicle and pars screws require accurate placement to avoid injury to nearby neurovascular structures. Freehand, fluoroscopically guided, and computed tomography (CT)-based navigation techniques have been described in the medical literature.
The present study aims to compare the safety and accuracy of the freehand technique versus stereotactic navigation for the placement of C2 pedicle and pars screws.
This study was a retrospective review of consecutive patients treated with posterior fixation constructs.
A total of 220 consecutive patients were treated with posterior fixation constructs containing C2 pars or pedicle screws placed at our institution.
Computed tomography imaging was used to assess the accuracy of screw placement. Intraoperative complications and incidence of stroke or mortality within 30 days of the operation were analyzed.
A retrospective review was conducted of consecutive patients treated with posterior fixation constructs containing C2 pars or pedicle screws placed by spine surgeons between January 1, 2010, and August 31, 2016. Clinical and radiographic data were collected and analyzed. Screw accuracy was graded independently by two reviewers according to the following criteria: grade A (no breach), grades B-E (breach with transverse foramen obstruction of 1%-25%, 26%-50%, 51%-75%, or 76%-100%, respectively), and grade M (medial breach). Screws were divided into acceptable (grades A and B) and unacceptable (grades C-E and M).
A total of 426 C2 pars or pedicle screws (312 freehand, 114 navigated) were placed in 220 patients (160 freehand, 60 navigated). Complications were similar between the groups: three vertebral artery injuries (two [1%] freehand, one [2%] navigated; p>.99), five deaths (four [3%] freehand, one [2%] navigated; p>.99), and one (2%) stroke in the navigated group (p=.61). Computed tomography imaging was available for accuracy grading of 182 screws (131 freehand, 51 navigated). No breaches (grade A) occurred in 113 of the freehand screws (86%) and in 34 of the navigated screws (67%) (p=.006). More screws had acceptable placement in the freehand group (123 of 131, 94%) than in the navigated group (42 of 51, 82%) (p=.02).
In patients with postoperative CT imaging (43%), the freehand technique was found to be more accurate than CT-based navigation for C2 pedicle or pars screw placement. Complication rates did not differ between the two techniques in this study.