C1-C2 Transarticular Screw Placement Research Articles

Different C2 screw placement techniques with mobilization of the vertebral artery in high-riding vertebral artery cases: Cadaver dissection.

In neurosurgery, posterior approaches intended at the craniovertebral junction are frequently used. The most popular procedures for treating upper cervical instability are C1 lateral mass, C2 pedicle, and C1-C2 transarticular screw stabilization. Due to their proximity to neural structures and the presence of the high-riding vertebral artery (VA), these techniques are complicated. The risk of VA damage can be decreased by mobilizing the VA. Using cadaveric specimens in this study was aimed to demonstrate C2 pedicle and C1-C2 transarticular screw placement with VA mobilization and a novel C2 inferior corpus screw placement technique. In this study, twelve adult cadaveric specimens and two adult dry cadaveric C2 bones were used with the permission and decision of the University Research Ethics Committee. Colored silicone was injected into the arteries and veins of these twelve cadaveric specimens. Then, muscle dissection was performed stepwise, and the C2 vertebrae of the cadavers were revealed with a surgical microscope. Each specimen and entire stages of the dissections were recorded photographically. After cadaver dissections, screw placement was performed with three different techniques. Finally, radiological imaging was done with fluoroscopy. After dissection, the lateral mass of the C2 vertebra was observed, and lateral to it, the transverse process and foramen were detected with the help of a hook. Next, the posterior wall of the VA groove was removed using a 1 mm thin plate Kerrison rongeur until the VA loop could partially be observed the VA. This enables us to find the top of the loop of the VA and mobilize it inferiorly using a dissector. Following this step, the C1-2 transarticular, C2 pedicle, and the novel C2 inferior corpus screw placement can be performed safely by directly visualizing the artery. Due to the nearby neurologic and vascular structures, placing the C2 pedicle and C1-2 transarticular screw is a challenging procedure, especially in high-riding VA cases. However, it is possible to place the C2 pedicle, C1-2 transarticular, and novel C2 inferior corpus screw after the mobilization of the VA. This study aimed to show all of them together on a cadaver for the first time, to understand the anatomy of the C2 vertebra, and to use screw placement techniques to minimize the risk of complications.

Referencing for anterior atlantoaxial trans-articular osteosynthesis: a radiological study and proposal of a decisional algorithm.

Anterior trans-articular C1-C2 screw placement can be considered as a surgical alternative in different conditions affecting the atlantoaxial region. While its rigidity is similar to posterior Magerl and Harms techniques, it also provides some surgical advantages. However, the literature lacks papers exhaustively describing indication criteria, surgical steps, and pitfalls. This is a radiological study on 100 healthy subjects. Thin-layer CT scans of the craniovertebral junction were retrieved from the institutional database. The coronal inclination of the C1-C2 joint rim and the depth of the entry point of the screw with respect to the anterior profile of C2 were measured. The antero-posterior and the medio-lateral surgical corridors for the screw placement, and the wideness of the target area on the upper surface of C1 were also measured. The multivariate analysis showed that the coronal inclination of the C1-C2 articular joint rim strongly influences the surface extension of the C1 target area; the depth of the entry point and the C1-C2 articular rim inclination seem to be independent factors in influencing both the medio-lateral and the antero-posterior surgical corridors wideness. A decisional algorithm on whether to perform an anterior or posterior approach to the atlantoaxial region was also proposed. We can conclude that, as much as the C1-C2 articular rim is tending to the horizontal line, and as deeper is the entry point of the screw on the anterior profile of C2, as easier the anterior C1-C2 trans-articular screw placement will result.

Deviation Analysis of C1–C2 Transarticular Screw Placement Assisted by a Novel Rapid Prototyping Drill Template

Cadaveric study. The aim of this study was to develop and validate the accuracy of a novel navigational template for C1-C2 transarticular screw (C1C2TAS) placement in cadaveric specimens. Currently, C1C2TASs are primarily positioned using a free-hand technique or under fluoroscopic guidance. Screw placement is challenging owing to the small size of the C2 isthmus, which places technical demands on the surgeon. Screw insertion carries a potential risk of neurovascular injury, magnifying the importance of using a precise technique for screw insertion. Computed tomography (CT) scans with 0.625-mm wide cuts were obtained from the 32 cadaveric cervical specimens. The CT data were imported into a computer navigation system. We developed 32 three-dimensional drill templates, which were created by computer modeling using a rapid prototyping technique based on the CT data. We constructed drill templates using a custom trajectory for each level and side based on specimen anatomy. The drill templates were used to guide establishment of a pilot hole for screw placement. The entry point and angular direction of the intended screw positions and inserted screw positions were measured by comparing postoperative and preoperative images after the coordinate axes were synchronized. The average displacement of the entry point of the left and right C1C2TAS in the x-, y-, and z-axis was 0.13±0.90 mm, 0.50±1.50 mm, and -0.22±0.71 mm on the left, and 0.21±1.03 mm, 0.46±1.55 mm, and -0.29±0.58 mm on the right. There was no statistically significant difference in entry point and direction between the intended and actual screw trajectory. The small deviations seen are likely due to human error in the form of small variations in the surgical technique and use of software to design the prototype. This technology improves the safety profile of this fixation technique and should be further studied in clinical applications.

A Comparison C1–C2 Transarticular Screw Placement After Self-Education and Mentored Education of Orthopaedic Residents

Prospective randomized trial. This study will provide preliminary data on whether residents can be "self-taught" and to what extent a lecture, demonstration, and coaching can improve skills and knowledge. Practice-based learning is an essential competency in Accreditation Council for graduate Medical Education-accredited residencies. Little has been done to demonstrate whether residents can be self-taught or benefit from mentoring in understanding and performing difficult surgical tasks. A written test was given to orthopedic residents on C1-C2 transarticular screw placement. They were then provided reading on C1-C2 transarticular screw placement. Residents were then divided into a "self-directed learning" group and a "mentored learning" group. All residents then performed the technique on models, with the "mentored" group receiving a lecture and coaching from the mentor. The models were analyzed for technique errors and the previous test was administered again as a posttest. The test and screw placement were repeated 4 months later. Residents without mentoring had an average improvement of 4.5 points, those with mentoring had average improvement of 8.6 points (P=0.0068). The screw placement technique error rate for the nonmentored group (n=8) was 2.55, and for the mentored group (n=9) was 1.47 (P=0.004). Sixteen residents completed the delayed test, 7 from the nonmentored groups and 8 from the mentored group. Nine residents were able to repeat the screw placement technique 4 months after the initial test and screw placement, 3 nonentored, and 6 mentored. Although there were some trends toward the mentored group having better retention, neither knowledge nor skill was statistically different. This preliminary trial seems to indicate that residents provided a lecture and guided technical instruction will obtain knowledge and perform procedures better than those that do not. Conclusions based upon Post Graduate year, motivation, and interest in spine surgery could not be made.

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

Background contextInjury to the internal carotid artery (ICA) is a potentially catastrophic complication of C1-lateral mass (C1-LM) or C1–C2 transarticular screw insertion. PurposeThis study was designed to determine the risk of injury to the ICA during placement of these screws using computed tomography angiography (CTA). Study designRadiographic analysis using CTA. Patient sampleOne hundred sixty CTAs were examined, for a total of 320 ICAs. Outcome measuresNot applicable. MethodsFine-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. ResultsThe 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. ConclusionsBicortical 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.

The anatomical and clinical study on anterior C1-C2 transarticular screw fixation for the treatment of traumatic instability of CI-2 joint

Objective To provide anatomic data for anterior C1-C2 transarticular screw fixation and clarify its curative effect in curing the patients with C1-C2 instability.Methods Direct measurements were taken from 100 pairs of dried Chinese human C1 and C2 vertebrae and 11 patients who had C1-C2 traumatic instability were operated on with anterior C1-C2 transarticular screw fixation technique.Results In the anterior C1-C2 transarticular screw placement,the lateral angulation of the screw placement rela-tive to sagittal plane ranged from (5.5±2.0)° to (23.6±2.1)° on average.The posterior angulation rel-ative to the coronal plane ranged from (14.9±2.6)° to (25.6±2.5)°.The length of the medial screw path ranged from (16.58±1.49) to (26.44±1.75) mm.In the 11 patients, one patient with cervical cord trauma was died of pulmonary infection one month later,and the remaining 10 patients were followed up for about 7 months to 3 years (mean 17 months).They all had no trauma on vertebral artery and cervi-cal cord during their cervical operations.All these eases had atlantoaxial synostoses.Conclusion The an-terior C1-C2 transarticular screw fixation was not only manipulated easily,but also had a less risk of inju-ring vertebral artery and cervical cord.It provides a new treatment of internal fixation for the patients with atlantoaxial instability. Key words: Atlantoaxial joint; Internal fixation; Screw; Anatomy

Anomalous Vertebral Artery at the Extraosseous and Intraosseous Regions of the Craniovertebral Junction

This study examined the extraosseous and intraosseous anomalies of vertebral arteries in patients who underwent surgery of the craniovertebral junction. To describe the usefulness of three-dimensional computed tomography angiography for evaluating vertebral artery anomalies before surgery. Previous studies using catheter angiograms have identified anomalous courses of the vertebral artery at the craniovertebral junction. Studies using computed tomography reconstruction also showed deviation of the vertebral artery groove at the C2 isthmus, demonstrating a risk of vertebral artery injury for C1-C2 transarticular screw placement. These analyses provided us with useful information for identifying anomalies of the vertebral artery, but they could not visualize the artery and its circumferential osseous tissue simultaneously, nor could they analyze the reciprocal anatomy of both tissues. Thirty-one consecutive patients who submitted to surgery at the craniovertebral junction were evaluated before surgery by three-dimensional computed tomography angiography. Eleven of the patients had congenital osseous anomalies at the craniovertebral junction including os odontoideum and ossiculum terminale. Anomalous vertebral arteries at the extraosseous region were visualized by three-dimensional reconstruction images, and the intraosseous deviation of the vertebral artery at the C2 isthmus was evaluated by multiplanar reconstruction images. Extraosseous and/or intraosseous vertebral artery anomalies were detected in 9 cases. Eight of the 9 cases had osseous anomalies at the craniovertebral junction. Abnormal courses of the vertebral artery at the extraosseous region were detected in 4 cases: 2 had fenestration and 2 had persistent first intersegmental artery. Asymmetry of bilateral vertebral arteries was found in 5 cases: the right was dominant in 3 cases and the left in 2 cases. A high-riding vertebral artery at the C2 isthmus was detected in 5 cases. Based on these findings, we modified our surgical approach and the screw placement; consequently, no vertebral artery injury occurred. In patients having osseous anomalies at the craniovertebral junction, the frequency of vertebral artery anomalies at the extraosseous and intraosseous regions is increased. With preoperative three-dimensional computed tomography angiography, we can precisely identify the anomalous vertebral artery and reduce the risk of intraoperative injury to the vertebral artery, in advance.

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%.

P105. Posterior atlantoaxial stabilization: a new alternative to C1-2 transarticular screws

Abstract Purpose of study: Develop new techniques to improve safety and success of C1–C2 fusion procedures. Methods used: A standard posterior C1–C2 exposure is performed. Cross-table lateral fluoroscopy is used to guide and confirm screw trajectories. The C2 pedicle screw entry point is identified and drilled with angles 15 degrees medially and 25 degrees cephalad for pedicle cannulation. Drill depth is stopped short of the C2 transverse foramen. The C1 lateral mass screw insertion point is located beneath the posterior arch of C1 in the midposition of the lateral mass just above the C2 root. The drill is then angled 10 degrees medial to lateral and cephalad toward the anterior tubercle of C1 on lateral fluoroscopy. The C1–C2 joint is then decorticated and packed with local bone fragments. Posterior rods are contoured and connected to polyaxial screw heads, and a cross-connector is applied. of findings: This technique has been used in five cases of atlantoaxial instability at our institution during the past year. There have been no C2 nerve root or vertebral artery injuries. No construct failures have been observed during the current follow-up. Relationship between findings and existing knowledge: C1 lateral mass and C2 pedicle screw fixation offers an alternative means of atlantoaxial fusion. The technique is less demanding than C1–C2 transarticular screw placement and reduces the risk of vertebral artery injury. The linked construct is stable in flexion, extension and rotation. Laminectomy or fracture of the posterior elements does not preclude this fixation technique. We think this procedure will replace the C1–C2 transarticular screw procedure. Overall significance of findings: This new technology has the potential to supplant previous C1–C2 procedures with improved safety and success. Disclosures: Device or drug: pedicle screws. Status: approved. Conflict of interest: No conflicts.

Posterior atlantoaxial stabilization: a new alternative to C1–C2 transarticular screws

Purpose of study: Develop new techniques to improve safety and success of C1–C2 fusion procedures.Methods used: A standard posterior C1–C2 exposure is performed. Cross-table lateral fluoroscopy is used to guide and confirm screw trajectories. The C2 pedicle screw entry point is identified and drilled with angles 15 degrees medially and 25 degrees cephalad for pedicle cannulation. Drill depth is stopped short of the C2 transverse foramen. The C1 lateral mass screw insertion point is located beneath the posterior arch of C1 in the midposition of the lateral mass just above the C2 root. The drill is then angled 10 degrees medial to lateral and cephalad toward the anterior tubercle of C1 on lateral fluoroscopy. The C1–C2 joint is then decorticated and packed with local bone fragments. Posterior rods are contoured and connected to polyaxial screw heads, and a cross-connector is applied.of findings: This technique has been used in five cases of atlantoaxial instability at our institution during the past year. There have been no C2 nerve root or vertebral artery injuries. No construct failures have been observed during the current follow-up.Relationship between findings and existing knowledge: C1 lateral mass and C2 pedicle screw fixation offers an alternative means of atlantoaxial fusion. The technique is less demanding than C1–C2 transarticular screw placement and reduces the risk of vertebral artery injury. The linked construct is stable in flexion, extension and rotation. Laminectomy or fracture of the posterior elements does not preclude this fixation technique. We think this procedure will replace the C1–C2 transarticular screw procedure.Overall significance of findings: This new technology has the potential to supplant previous C1–C2 procedures with improved safety and success.Disclosures: Device or drug: pedicle screws. Status: approved.Conflict of interest: No conflicts.

4:04 Circumferential reconstruction of the cervical spine

Purpose of study: A significant number of adults have pain, cosmetic deformity or neurologic injury related to cervical malalignment. The majority of such cases involve sagittal plane malalignment with loss of lordosis, kyphosis or double curve (swan-neck) deformity of the subaxial spine. A smaller number of patients have coronal plane malalignment or scoliosis in the subaxial spine or various anomalies of the occipitoatlantoaxial complex. In the following, we describe 50 cases within the past 5 years in which circumferential approaches have been applied for the correction of cervical deformities.Methods used: At our institution, more than 50 cases of multisegmental cervical or occipitocervical deformity corrections have been performed since 1995. Thirty cases have at least 24 months of follow-up. Causative pathologies include rheumatoid arthritis, congenital dysplasias, late posttraumatic deformity, iatrogenic postsurgical deformity, severe degenerative disease, tumors, vascular malformations and infections. All subaxial cases involved sagittal plane restoration. One in four also required coronal or axial realignment. Two thirds of occipitoatlantoaxial cases involved sagittal corrections; half with axial or coronal restoration as well. Two thirds of all cases, including 540 degree reconstructions, could be completed in a single day with a single anesthetic.of findings: An aggressive approach to anterior and posterior osteotomy followed by anterior distraction and posterior compression allowed correction of kyphotic deformity in all subaxial cases. Partial loss of correction occurred in one third of cases secondary to cage or strut settling or telescoping, despite rigid fixation. Intraoperative correction of coronal or axial deformities was maintained with little, if any, subsequent loss. Rigid screw fixation to the suboccipital keel and to the C1–C2 region with long C2 pars screws or C1–C2 transarticular screws allowed maintenance of intraoperative correction with no apparent late loss. There were no deaths and no spinal cord or nerve root injuries in this series. Two vertebral artery injuries related to C1–C2 transarticular screw placement occurred; one resulted in a delayed Wallenburg's syndrome. Two next-segment failures occurred, requiring reoperation for extension of fusion. There was a measurable loss of anterior distractive height restoration in one third of cases over time. In no case was this clinically significant. Anterior cage or strut settling occurred with both rigid and dynamic anterior buttresses and in the face of rigid anterior and posterior hardware.Relationship between findings and existing knowledge: The literature on spinal deformity is largely concerned with thoracic and thoracolumbar pathology. Traditional surgical approaches to cervical deformity using nonrigid internal fixation with wire or cable and/or semirigid external fixation in halo vests or Minerva casts were of limited use in the correction of deformity in any plane either above or below C2.Overall significance of findings: Modern reconstructive techniques allow for clinically significant correction of cervical and occipitocervical deformities associated with chronic pain, cosmetic deformity and neurologic deficit. An aggressive circumferential approach to decompression and osteotomy allows near-anatomic correction of geometric deformity in any plane.Disclosures: No disclosures.Conflict of interest: No conflicts.

Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws.

This study examines the C2 vertebrae using both direct anatomic and computed tomographic measurements. To define the relation of the C2 vertebrae bony elements to the vertebral artery and the spinal canal, to determine individuals at risk for vertebral artery injury during C1-C2 transarticular screw placement. Recent literature assessing the safety of upper cervical spine transarticular screws has concentrated on technique, including the optimal point of entry and path projection of the screw. The actual dimensions of the C2 isthmus of the pars interarticularis has not been examined in a large number of specimens. C2 isthmus width and height measurements were made on 205 human cadaveric C2 vertebrae. Vertebrae predicted to be at risk for vertebral arterial injury were imaged by computed tomography. There were 102 female and 103 male specimens with mean isthmus widths of 8.2 +/- 1.5 mm and 7.2 +/- 1.3 mm, respectively. Five specimens (2.4%) had an isthmus width less than 5 mm. The mean isthmus heights were 8.6 +/- 2.0 mm and 6.9 +/- 1.5 mm for male and female specimens, respectively. In twenty-four specimens (11.7%), one or both isthmi had a height of less than 5 mm. Six of these specimens were male and 18 were female. The right C2 isthmus was generally smaller than the left. Computed tomographic measurements closely approximated those of the actual dimensions of the isthmi. Placing a 3.5 mm screw in a patient with narrow C2 isthmus dimensions (smaller than 5 mm in either the height or width) is technically difficult. Because of narrow C2 isthmus width and/or height, approximately 10% of patients may be at risk for a vertebral artery injury with placement of C1-C2 transarticular screws.

Safety and accuracy of transarticular screw fixation C1-C2 using an aiming device. An anatomic study.

In this anatomic study, the safety and accuracy of C1-C2 transarticular screw placement was tested in a normal anatomic situation in cadaver specimens using a specially designed aiming device. To assess the safety and accuracy of transarticular screw placement using the technique described by Magerl and a specially designed aiming device. Transarticular C1-C2 screw fixation has been shown to be biomechanically superior to posterior C1-C2 wiring techniques. Several clinical series have been reported in the literature. However, no previous study assessing the accuracy or safety of this technique has been published. Structures at risk are the vertebral arteries, spinal canal, and the occiput-C1 joint. Five frozen human cadaveric specimens were thawed and instrumented with 10 C1-C2 transarticular screws, according to the technique described by Magerl but using a specially designed aiming device described by the senior author (Jeanneret). After screw placement, the accuracy of screw positioning and the distance of the screws from the spinal canal, vertebral arteries, and atlanto-occipital joint were determined by anatomic dissection and radiographic analysis. The structure at greatest risk was the atlanto-occipital joint, with one screw found to be damaging the joint. Vertebral artery or spinal canal penetration was not observed in any of the specimens. Screw length averaged 45 mm and, with proper length, the screw tip was found to be located approximately 7.5 mm behind the anterior tubercle of C1 on lateral radiographs. This anatomic study demonstrates that C1-C2 transarticular screw fixation can be performed safely in a normal anatomic situation by surgeons who are familiar with the pertinent anatomy. The aiming device allowed safe instrumentation in all patients. In case of an irregular anatomic situation (e.g., congenital abnormalities or trauma), computed tomographic scan with sagittal reconstruction is recommended-in particular, to obtain information about the course of the vertebral artery.