C2 Pedicle Screw Research Articles

The C2 "Parsicle" Screw: Introduction of a Novel Posterior Surgical Technique For Upper Cervical Fixation.

The instrumentation of C2 is technically challenging given the anatomic complexity of the upper cervical spine. Although the placement of C2 pedicle screws may be safer than transarticular screw placement, the inconsistent location of the transverse foramen and vertebral artery precludes placement of such screws in up to 26% of patients. In cases where vertebral artery anatomy prevents the safe placement of a pedicle screw, a pars screw is an excellent alternative. However, pars screws must stop short of the vertebral foramen, limiting the typical length of these screws to only 14-18 mm. The associated purchase and rigidity are compromised compared with the pedicle screw. A modified C2 fixation technique was developed by our group which we have named the C2 "parsicle" screw reflecting the hybrid nature of the screw incorporating aspects of pars and pedicle screw fixation.

Safety and Accuracy of the Freehand Placement of C7 Pedicle Screws in Cervical and Cervicothoracic Constructs.

Background: Cervical pedicle screws are advantageous in their biomechanical stability within cervical and cervicothoracic constructs. The seventh cervical vertebra contains relatively large pedicles and has a low incidence of vertebral artery localization within the transverse foramina. The freehand technique of pedicle screw insertion is advantageous in decreasing intraoperative radiation exposure both to the patient and surgeon. In this study, we investigated the safety and accuracy of C7 pedicle screw placement at our institution utilizing an anatomic freehand technique.Methods and Materials: A retrospective study was performed, and 20 patients were identified who met the inclusion criteria over a five-year period (2013-2018). The C7 pedicle screw placement capability and accuracy were recorded. Accuracy was graded based upon postoperative imaging on a Grade 0-3 scale for breach assessment. Any neurologic complications related to screw placement were also recorded.Results: Successful pedicle screw placement occurred in 90% of attempts (36/40). The overall screw accuracy rate was 89% (32/36). There were four minor breaches (Grade 1) identified on CT, without neurologic complications. The fusion rate in our cohort for patients with follow up greater than eight months was 100%.Conclusions: In our patient series, the freehand technique of C7 pedicle screw placement utilizing a small laminotomy with direct pedicle palpation appears to be a safe and accurate method for screw placement, and provides adequate biomechanical stability for cervical and cervicothoracic construct fusion.

Intraoperative imaging and navigation for C1-C2 posterior fusion.

Background:Cervical axial spine fusion is challenging as the anatomy is extremely variable, and screw misplacement can lead to severe complications. C1 lateral mass screws and C2 pedicle screws are routinely placed under either fluoroscopic guidance or imaging-assisted navigation. Here, we compared the two for axial screw placement.Methods:We retrospectively evaluated patients’ treated from 2011–2016 utilizing the Harm’s procedure for C1-C2 screw fixation performed under either fluoroscopic guidance (nine patients) or image-assisted O-arm navigation (five patients). The groups had similar demographic and risk factors. Variables studied included operative time, estimated blood loss (EBL), accuracy of screw placement, screw reposition rates, and reoperation rates.Results:The mean EBL was 555CC and 260CC, respectively (not a significant difference) utilizing fluoroscopic versus O-arm navigation. Of interest, the mean surgical duration was 27 min longer in the O-arm versus fluoroscopy group (P = 0.03). Ten C2 pedicle screws were performed using O-arm navigation. Alternatively, as 9 of 18 C2 pedicles were considered “risky” for the placement of fluoroscopic-guided pedicle screws, laminar screws were utilized. Although the accuracy rate of C1 and C2 screw placement was higher for the navigated group, this finding was not significant. Similarly, despite complications involving two unacceptably placed screws from the fluoroscopic guidance group, there were no neurological sequelae.Conclusion:Axial cervical spine instrumentation is challenging. Utilization of Imaging-assisted navigation increases the accuracy and safety of screw placement.

Suboccipital neuralgia after C1 pedicle screw insertion: do we neglect atlantooccipital joint violation? - Case report and literature review

BackgroundOccipital neuralgia is one of the postoperative complications of C1 lateral mass screw insertion, which was deemed to be related with the C2 nerve root dysfunction.Case presentationA 52-year-old female patient presented with gradually progressive numbness and weakness in her extremities for 6 months. X-ray and computed tomography (CT) scan revealed obvious anterior atlantoaxial dislocation (ADD), which was reducible on extensive view. Atlantoaxial pedicle screw fixation and bone graft was performed. Immediately after the operation, the neurological symptom significantly improved. The patient complained of restricted cervical rotation and suboccipital neuralgia which was exacerbated by rotation with an intensity of 7 on a visual analog scale (VAS) ranging from 0 to 10 at postoperative day 5. While a satisfactory reduction was detected in the postoperative CT, violation of the left atlantooccipital joint was observed in the left C1 screw. Nimesulide (daily dosage of 0.2 g) and bracing were recommended immediately. At the 2 month follow-up, both the neurological improvement and reduction were maintained. The VAS of suboccipital neuralgia is 3 and decreased to 1 at 6 months postoperative. Bony fusion of the left atlantooccipital joint was confirmed by CT scan at 6 months postoperative. The patient complained that the suboccipital neuralgia was tolerable without the assistance of braces or medications for pain. At the 18 month follow-up, only stiffness of head flexion and rotation was observed without suboccipital neuralgia.ConclusionSuboccipital neuralgia after atlantooccipital joint violation of C1 pedicle screw placement most likely results from C1 nerve root irritation. As the corresponding dermatome differs from the distributing region and aggravated factor of C2 nerve root dysfunction, neuralgia due to C1 irritation was only localized at suboccipital region and exacerbated by rotation.

Comparison of Axial Symptoms and Limitations of Activities of Daily Living Accompanying Reduced Neck Mobility After Cervical Laminoplasty Preserving C2 Muscle Attachments With and Without C2 to T1 Instrumented Fusion.

ObjectiveMuscles are usually detached from C2 to facilitate C2 pedicle screw insertion. The aim of this study was to compare 1-year postoperative axial symptoms and limitations in activities of daily livings (ADLs) accompanying reduced neck mobility between 2 procedures in which all C2 muscle attachments are preserved: laminoplasty and C2 to T1 fusion (LPF group: n=15) and laminoplasty alone (LP group: n=26). MethodsWe examined axial symptoms and limitations in ADLs using the Japanese Orthopedic Association Cervical Myelopathy Evaluation Questionnaire. We also examined related factors, including the occiput (O)–C7 angle in extension and flexion, and the rotational and O–C2 ranges of motion (ROM). ResultsThe postoperative decreases in the O–C7 angle in flexion (27.8° vs. 9.4°) and rotational ROM (40° vs. 15°), as well as the compensating postoperative increase in the O–C2 ROM (11.7° vs. 2.3°), were significantly greater in the LPF group. Most of the axial symptoms were similar between groups. The ability to perform ADLs tended to worsen more frequently in the LPF group, but the difference did not achieve significance. ConclusionPostoperative changes in axial symptoms and loss of ROM were not obstacles affecting patients’ ability to perform ADLs after laminoplasty with muscle-sparing C2 to T1 fusion.

Occipitocervical or C1-C2 fusion using allograft bone in pediatric patients with Down syndrome 8 years of age or younger.

Sufficient internal fixation for occipitocervical (OC) or C1-C2 instability in pediatric patients with Down syndrome is difficult owing to small osseous structures, congenital deformities, and immature ossification. The purpose of this study was to evaluate the clinical outcomes of patients aged 8 years or younger with Down syndrome who underwent OC or C1-C2 fusion using freeze-dried allograft as bone graft substitute. The participants included seven consecutive patients aged 8 years or younger with Down syndrome who were treated for upper cervical disorders with posterior OC or C1-C2 fusion using freeze-dried allografts at our hospital between 2007 and 2016 and had a minimum follow-up of 1 year. Postoperative flexion/extension cervical radiography and computed tomography were repeated at 3 months after surgery before removal of the collar. The modified McCormick scale was used to grade functional status. The seven patients had an age range of 5-8 years (mean: 5.9 years). The mean follow-up period was 36 months (12-120 months). Six patients had os odontoideum and one had basilar invagination. Three patients underwent C1-C2 fusion, and in all cases, bilateral C1 lateral mass screws and bilateral C2 pedicle screws were used. Four patients underwent OC fusion, and in three of these cases, occipital and bilateral pedicle screws were used. One patient underwent reoperation because of occipital screw back-out with autograft; therefore, C2 lamina screws were added to pedicle screws. Solid bony fusion was achieved, and stable constructs were maintained on radiography in all patients, without infection or implant failure. In this study, we used freeze-dried allograft as a bone graft substitute, and we were able to detect bony trabeculae at the graft-recipient interface on lateral cervical radiographs and on reconstructed sagittal computed tomographic images in all patients. These results suggest that use of allograft is effective for treatment of upper cervical spine abnormalities in pediatric patients with Down syndrome.

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.

Ten-Year Results of Reconstruction for Rheumatoid Cervical Spine Lesions and Occurrence Factor of Subaxial Subluxation.

Study DesignRetrospective chart review.PurposeThis study evaluated long-term surgical outcomes of computer-assisted reconstruction using transarticular or cervical pedicle screws for cervical spine lesions caused by advanced rheumatoid arthritis (RA).Overview of LiteratureWe routinely employ C1–C2 transarticular and cervical pedicle screw instrumentation to reconstruct advanced and unstable RA cervical lesions. However, few reports are available on the long-term results of surgical reconstruction for rheumatoid cervical disorders, particularly regarding cervical pedicle screw fixation.MethodsSix subjects (all female) with RA cervical lesions who underwent atlantoaxial or occipitocervical fixation and were followed for at least 10 years were retrospectively studied. A frameless, stereotactic, optoelectronic, computed tomography-based image guidance system was used for correct screw placement. Variables including the Japanese Orthopaedic Association score, EuroQol, Ranawat value, and C2–C7 angle before and 2, 5, and 10 years after surgery were assessed along with the occurrence of subaxial subluxation (SAS).ResultsMean age at initial surgery was 58.2±7 years (range, 51–68 years), and mean follow-up period was 141±11 months (range, 122–153 months). Lesions included atlantoaxial subluxation (AAS, n=2) and AAS+vertical subluxation (n=4). Mean C2–C7 lordotic angle before and 2, 5, and 10 years after surgery was 20.1°±6.1°, 21.0°±4.0°, 18.8°±4.7°, and 17.8°±5.3°, respectively. SAS did not occur in cases maintaining the C2–C7 lordotic angle. In two cases where the C2–C7 lordotic angle declined from 5 years postoperatively, SAS occurred at the C2–C3 level in one and at the C4–C5 level in the other, both of which required reoperation.ConclusionsPatients with rheumatoid cervical lesions who undergo atlantoaxial or occipitocervical fixation using C1–C2 transarticular or pedicle screws carry a risk of SAS for up to 10 years postoperatively, which may require reoperation.

Accuracy and Safety in Screw Placement in the High Cervical Spine: Retrospective Analysis of O-arm-based Navigation-assisted C1 Lateral Mass and C2 Pedicle Screws.

This study was a retrospective analysis. The purpose of present study was to evaluate accuracy, efficiency, and safety of intraoperative O-arm-based navigation system for the placement of C1 lateral mass screw (C1LMS) and C2 pedicle screws (C2PSs) in high cervical spine operations. High screw misplacement rates, various pedicle morphometry and vertebral body size variations have led to a search of image-guided systems to improve the surgical accuracy of screw insertion in high cervical spine. The use of O-arm has been proposed for more accurate and efficient spinal instrumentation. Between June 2009 and August 2016, a total of 48 patients with atlantoaxial instability were surgically treated using the image-guidance system. To reconstruct atlantoaxial instability, we have been using Harm's technique of C1LMS and C2PS fixations. A frameless, stereotactic O-arm-based image-guidance system was used for correct screw placement. Postoperative computed tomographic scan with multiplanar reconstructions were used to determine the accuracy of the screw placement. A total of 182 screws, including 90 C1LMS and 92 C2PSs were inserted using image-guidance system. In total, 4.4% (4/90) of C1LMS and 7.6% (10/92) of C2PS had cortex violation over 2 mm and considered as "significant." Among the significant cortex violations, "unexpected breech" was 3.3% of all the screws inserted. Two (2.1%) screws inserted had perforated the vertebral artery canal and iatrogenic vertebral artery stenosis was proved with postoperative computed tomography angiography. When divided into time periods, 60% of significant breech occurred during the beginning stage, 40% during adaptation stage and none during expert stage. In this study, the authors demonstrated that use of image-guidance system seems to be beneficial for high cervical instrumentation which requires much experience and steep learning curves. However, incidence of cortex violation does not disappear completely due to the close proximity to spinal canal and surrounding vessels.

Surgical Treatment of Traumatic Type II Odontoid Fracture Using Polyaxial C1 Lateral Mass and C2 Pedicle Screws Fixation

Background Data: Posterior atlantoaxial fixation is indicated for C1-C2 instability or painful osteoarthritis. Different techniques were designed for atlantoaxial fixation as sublaminar wiring, transarticular screw fixation, and, recently, C1 lateral mass and C2 pedicle polyaxial screws and rod system. Purpose: To investigate the safety, advantages, and complications of posterior atlantoaxial fixation with polyaxial C1 lateral mass and C2 pedicle screws in C1-C2 instability. Study Design: A retrospective clinical case series. Patients and Methods: Fourteen consecutive patients, ten males and four females, with a mean age of 40.8±9.6 years were reported. All had traumatic C1-2 instability due to type II odontoid fractures and underwent posterior fixation with polyaxial C1 lateral mass and C2 pedicle screws. Nine patients suffered from motor vehicle accident (MVA) and 5 suffered from falls. All patients were neurologically intact except four patients who had neurological deficits. We used Japanese Orthopedic Association Score (JOA) for their functional evaluation. The average follow-up was 17±1.96 (range, 12–20 months). Operative time, operative blood loss, screw trajectory, screw length, and injury of neurovascular structures were reported. Fusion and construct stability were evaluated by plain radiography and/or CT. Visual Analogue Scale (VAS) of neck pain and JOA were used to evaluate the functional outcome. Results: The mean duration of surgery was 175.3±12.3 min. The mean blood loss was 553.6±106.5 ml and two patients required transfusion of one unit of blood. The mean length of C1 lateral mass and C2 pedicle screws were 30±1.6 mm and 16.4±1.8 mm, respectively. Correct screw placement and good stability were reported in all patients (100%) at the last follow-up. Mean neck pain on VAS was 2.8±0.8 and 2.3±0.5 at 6 and 12 months, respectively. The complications included moderate pain at iliac graft site for 3 months in 2 patients, pain and dysesthesia in C2 dermatome for 4 months in 3 patients, and superficial wound infection in 2 patients. Conclusion: Posterior atlantoaxial fixation with polyaxial C1 lateral mass and C2 pedicle screws is a safe and effective method in the treatment of traumatic atlantoaxial subluxation due to type II odontoid fractures. (2019ESJ176)

Motion Preserving Surgery Using O-Arm for Unstable Hangman Fracture

Abstract Aim To evaluate clinical outcomes, radiological findings (displacement and angulation), and bony fusion in cases of unstable hangman’s fracture. Introduction Hangman fracture, also known as traumatic spondylolisthesis of axis vertebra, is classically defined as bilateral pars interarticularis fracture of axis vertebra. Opinions vary regarding optimal treatment of unstable hangman’s fractures. Some authors have recommended use of rigid orthosis, whereas others have recommended internal fixation. The peculiar anatomy of the upper cervical spine is highly variable, and presence of surrounding neurovascular structures makes axis pedicle screw fixation even more technically challenging. The advent of intraoperative three-dimensional navigation systems facilitates safe and accurate instrumentation. Materials and Methods This article analyzes patients operated for type II and IIa hangman’s fractures during the period from September 2011 to August 2018 by two neurosurgeons. The patients’ age, sex, mechanism of injury, associated injuries, and neurologic status were noted. The authors retrospectively assessed the clinical outcome, radiological findings (displacement and angulation), and bony fusion. Result Eighteen patients with age ranging from 17 to 81 years, were operated using computed tomography-based (O-arm) navigation. Accuracy of screw insertion, preoperative and postoperative displacement, and angulation of C2 over C3 were evaluated. Bony fusion was assessed in all patients. A total of 92 screws were inserted: 36 screws in C2 pedicle, 34 in C3 lateral mass, 20 in C4 lateral mass, and 2 in C5 lateral mass. Of these 92 screws, 36 C2 pedicle screws were inserted under O-arm guidance. The mean preoperative C2–C3 displacement was 4.5 ± 2.1 mm, and the mean postoperative displacement was 1.8 ± 1.1 mm with a mean reduction of 2.7 ± 1.4 mm. The mean preoperative C2–C3 angulation was 10.2 ± 7.6 degrees and the postoperative angulation was 2.52 ± 4.62 degrees with a mean reduction of 8.2 ± 11.6 degrees. Screw malplacement was seen in two C2 pedicle screws (2/36, 5.5%). All C2 pedicle screw breaches were of grade 2. Excellent anatomical reduction in all cases could be achieved as established by the improvement in morphological parameters of fracture. Conclusion This series using O-arm in unstable hangman fracture demonstrates that intraoperative O-arm-based navigation is a safe, accurate, and effective tool for screw placement in patients with unstable hangman fracture.

Guideline for Posterior Atlantoaxial Internal Fixation Assisted by Orthopaedic Surgical Robot.

Atlantoaxial transarticular facet screw fixation (Magerl technique) and C1 lateral mass screws combined with C2 pedicle screws fixation (Harms technique) are the most commonly used techniques for posterior internal fixation in the upper cervical spine. Upper cervical spinal surgery is a technically demanding and challenging procedure because of complicated anatomical structures and frequent occurrence of anomalies. Accurate insertion of screws allows for stable and secure internal fixation, which is necessary for both techniques. Traditional methods under fluoroscopic assistance in this region cannot meet the requirements of high levels of accuracy and security during the procedure. Robot‐assisted spinal surgery can provide accurate and reliable guidance during the screw insertion, which is evidenced in the literature. As a recently developed technique, robot‐assisted surgery is supposed to be performed by skilled surgeons who have received standard training for robotic surgery. The standardized upper cervical spinal surgery assisted by the robot system needs to be introduced to these surgeons. Based on the consensus of consultant specialists, the literature review, and our local experience, this guideline included the introduction of the robotic system, the workflow of robot‐assisted procedures, and the precautions to take during procedures. This guideline aims to provide a standardization of the robotic surgery for posterior atlantoaxial internal fixation.

Epidemiology of Iatrogenic Vertebral Artery Injury in Cervical Spine Surgery: 21 Multicenter Studies

The overall incidence of iatrogenic vertebral artery injury (IVAI) in cervical spine surgeries (CSSs) is reported to be 0.07%-1.4%. Although IVAI occurred during C1-2 fusion, there is no accurate information regarding the surgery-specific risk of IVAI. This study aimed to stratify incidence of IVAI by surgical method and evaluate the correlation between IVAI and its sequelae. This retrospective, multicenter study involved clinical and radiologic evaluations for IVAI. All CSSs performed between 2012 and 2016 were included; neck mass excision and pain intervention were excluded. Patient characteristics, diagnosis, surgical technique, complications, and presence of IVAI were collected. In IVAI cases, technique details, characteristics, and sequelae were investigated. This study included 14,722 patients with 15,582 CSSs in 21 centers. IVAIs were identified in 13 (0.08%) patients. Surgery-specific incidence of IVAI was 1.35% in cases involving C1-2 posterior fixation and 0.20% in cases involving C3-6 posterior fixation. Common injury mechanisms were screw-in (31%) and high-speed drilling (23%). Screw-related IVAI occurred in 9 (69%) patients, and IVAI of the C1 lateral mass and C2 pedicle screws occurred in 4 and 3 patients, respectively. Of 13 cases of IVAI, 3 (23%) involved cerebellar or stem infarction; the infarction had no substantial correlation with injury grade or dominancy. Overall incidence of IVAI in CSSs was 0.08%. C1-2 posterior fixation had the highest incidence of IVAI (1.35%). Although clinical results of IVAI can be highly variable, controlling risk factors of IVAI is important.

Implant failure of pedicle screws in long-segment posterior cervical fusion is likely to occur at C7 and is avoidable by concomitant C6 or T1 buttress pedicle screws

The aim of this study was to investigate the incidence and characteristics of implant failure in posterior cervical long-segment fusion surgery. We retrospectively reviewed 51 cases of posterior cervical long-segment fusion surgery that used pedicle screws, lateral mass screws, or laminar screws. The cranial end of the fusion was C2 or C3, and the caudal end of the fusion was C7 or T1. All patients were observed with CT scans at 6 months postoperatively. We evaluated the loosening and breakage of the implanted screws or rods. In the 51 patients, 257 pedicle screws, 9 laminar screws and 233 lateral mass screws were placed. Implant failure occurred in 25 patients (49.0%). Screw loosening was found in 42 screws (8.4%). Screw breakage occurred in 6 (1.2%) screws. The implant failures were particularly observed in both ends of the fusion level. When C7 was the end of the lower instrumented level, the incidence was 40% without C6 pedicle screws, 33% with unilateral C6 pedicle screws, and 0% with bilateral C6 pedicle screws. The present study revealed that the incidence of implant failures of the screws in long-segment posterior cervical fusion surgery was higher, especially in the caudal end of the fusion levels. In cases where C7 was the lowest instrumented vertebra, buttress screw insertion to C6 is recommended to avoid implant failure of C7 pedicle screws.

Differences in fixation strength among constructs of atlantoaxial fixation.

OBJECTIVETo avoid jeopardizing an aberrant vertebral artery, there are three common options in placing a C2 screw, including pedicle, pars, and translaminar screws. Although biomechanical studies have demonstrated similar strength among these C2 screws in vitro, there are limited clinical data to address their differences in vivo. When different screws were placed in each side, few reports have compared the outcomes. The present study aimed to evaluate these multiple combinations of C2 screws.METHODSConsecutive adult patients who underwent posterior atlantoaxial (AA) fixation were retrospectively reviewed. Every patient uniformly had bilateral C1 lateral mass screws in conjunction with 2 C2 screws (1 C2 screw on each side chosen among the three options: pedicle, pars, or translaminar screws, based on individualized anatomical consideration). These patients were then grouped according to the different combinations of C2 screws for comparison of the outcomes.RESULTSA total of 63 patients were analyzed, with a mean follow-up of 34.3 months. There were five kinds of construct combinations of the C2 screws: 2 pedicle screws (the Ped-Ped group, n = 24), 2 translaminar screws (the La-La group, n = 7), 2 pars screws (the Pars-Pars group, n = 6), 1 pedicle and 1 pars screw (the Ped-Pars group, n = 7), and 1 pedicle and 1 translaminar screw (the Ped-La group, n = 19). The rate of successful fixation in each of the groups was 100%, 57.1%, 100%, 100%, and 78.9% (Ped-Ped, La-La, Par-Par, Ped-Par, and Ped-La, respectively). The patients who had no translaminar screw had a higher rate of success than those who had 1 or 2 translaminar screws (100% vs 73.1%, p = 0.0009). Among the 5 kinds of construct combinations, 2 C2 pedicle screws (the Ped-Ped group) had higher rates of success than 1 C2 pedicle and 1 C2 translaminar screw (the Ped-La group, p = 0.018). Overall, the rate of successful fixation was 87.3% (55/63). There were 7 patients (4 in the Ped-La group and 3 in the La-La group) who lost fixation/reduction, and they all had at least 1 translaminar screw.CONCLUSIONSIn AA fixation, C2 pedicle or pars screws or a combination of both provided very high success rates. Involvement of 1 or 2 C2 translaminar screws in the construct significantly lowered success rates. Therefore, a C2 pars screw is recommended over a translaminar screw.

C1-C2 screw fixation in the patient with anomalous course of vertebral artery: Case report

Introduction. The atlantoaxial complex is a very complicated structure and open reduction of C1-C2 subluxation is very demanding. Atlantoaxial instability may result from the traumatic, inflammatory, neoplastic, congenital or degenerative disorders. Anatomy of the vertebral artery is essential for surgical approach and sometimes the placement of C2 pedicle screw is not possible. In these instances, the translaminar screw placement in C2 can provide an alternative fixation point in C2, without threatening injury to the vertebral artery. Case report. We presented 54- year-old patient with cervical myelopathy according to traumatic atlantoaxial subluxation. Computed tomography angiography showed a bilateral vertebral artery anomaly of ?high-riding? type. The patient was operated and the posterior C1-C2 screws fixation was used. Due to the vertebral artery anomaly C2 screws were translaminary inserted. Complete reduction of C1-C2 subluxation and excellent neurological improvement were achieved. Conclusion. Surgical treatment of C1-C2 subluxation is very challenging. Many techniques of atlantoaxial fixation have been developed. The use of C2 translaminar screw is an alternative method of fixation in the treatment of atlantoaxial instability, especially in cases with the vertebral artery anomaly.

Planning C2 pedicle screw placement with multiplanar reformatted cervical spine computed tomography.

Object:Careful preoperative planning with thin-slice computed tomography (CT) scan is useful for hardware placement at C2. Prior studies have shown considerable variability in the proportion of C2 vertebrae considered safe for pedicle screw placement, depending on the imaging technique used. Our work sought to more carefully define that proportion using a refined imaging technique on a large number of submillimeter CT scans.Materials and Methods:We reviewed 150 submillimeter cervical spine studies randomly selected from CT scans performed at a Level 1 trauma center. OsiriX™ image analysis software was used to propagate a 5-mm cylinder through the plane of the pedicle on paracoronal reformatted CT scans. Hounsfield unit attenuation was used to determine whether the cylinder violated the pedicle. Binomial data were generated to determine the proportion of pedicles that would allow safe screw placement.Results:We analyzed 300 pedicles in 150 patients. Using a standard C2 pedicle starting point, 32% of pedicles were breached by the 5-mm diameter cylinder. When screw trajectory was adjusted by moving the cylinder to fit the pedicle isthmus, establishing an optimized starting point, only 14% of pedicles were breached. Average pedicle length was 27.3 mm for screws that would have crossed the isthmus versus 13.2 mm for screws that would have stopped short due to potential breach.Conclusions:Findings of the current work suggest that preoperative imaging analysis or navigation can be useful adjuncts when anatomical variants are present.

Novel unilateral C1 double screw and ipsilateral C2 pedicle screw placement combined with contralateral laminar screw-rod fixation for atlantoaxial instability.

To investigate the anatomical and biomechanical feasibility of the unilateral C1 double screw [pedicle screw (PS) + lateral mass screw (LMS)] and ipsilateral C2 PS combined with contralateral C2 laminar screw (LS)-rod fixation for atlantoaxial instability by comparison with traditional posterior fixation methods. Fifteen sets of complete dry bony specimens of atlas were used for morphometric analysis. The working length, width and thickness of the C1 PSs and LMSs were manually measured. Ten fresh-frozen cervical spines (C0-C7) were used to complete the range of motion (ROM) testing in their intact condition, under destabilization and after stabilization by the following procedures: unilateral C1-C2 PS rod fixation (Group A), bilateral C1-C2 PS rod fixation (Group B), and unilateral C1 double screw and ipsilateral C2 PS combined with contralateral C2 LS rod fixation (Group C). The working thickness of the C1 PS was ≤ 3.5mm in only one (1/15 = 6.7%) specimen. The other parameters were > 3.5mm in all specimens. In the ROM test, all fixation groups showed significantly reduced flexibility in all directions compared with both the intact and destabilization groups. Further, Groups B and C showed better stability in all directions than Group A. However, no significant differences were observed between Groups B and C. The C1 unilateral lateral mass could mostly contain two screws(PS + LMS) with diameters ≤ 3.5mm. The novel technique of unilateral C1 double screw and ipsilateral C2 PS combined with contralateral C2 LS rod fixation provided better stability than unilateral PS rod fixation and similar as bilateral PS rod fixation. Therefore, it is a feasible salvage method that provides a new insight into atlantoaxial instability. These slides can be retrieved under Electronic Supplementary Material.

Splitting of the semispinalis capitis muscle as a less invasive approach for atlantoaxial fusion – A technical note

PurposeAtlantoxial fusion with screw rod constructs traditionally requires subperiostal dissection of the C1/C2 muscle attachments, which may lead to postoperative axial neck pain and intraoperative blood loss. We evaluate a potentially less invasive, muscle splitting approach for atlantoaxial fusion in a cadaver model. MethodsA technical feasibility study was performed in a human cadaveric specimen with standard surgical instruments and an operating microscope. Surgically relevant anatomical structures as well as final exposure of the C1, C1/C2 and C2 screw entry points are demonstrated. ResultsFollowing a midline skin incision, blunt mobilization and downward retraction of the trapezius and splenius capitis muscle is followed by a longitudinal split of the semispinalis capitis muscle. At the lower border of the rectus capitis posterior major and the obliquus capitis inferior muscle the entry points for C1 lateral mass, C1/C2 transarticular and C2 pedicle screw are exposed. ConclusionMinimal invasive splitting of the semispinalis capitis muscle allows adequate exposure of the screw entry points of C1, C1/C2 and C2 while preserving the intrinsic muscles of the back at the craniocervical junction.

Computed tomographic morphometric analysis of lateral inclination C1 pedicle screw for atlantoaxial instability patients with a narrow C1 posterior arch

Atlanto-axial instability (AAI) is a congenital or developmental condition that leads to instability/subluxation of the atlantoaxial joint. This study is performed to determine anatomic feasibility of trajectory L and help select an optimal screw trajectory in treating patients with AAI with a narrow C1 posterior arch. Sixty patients who underwent cervical three dimensional-computed tomography (3D-CT) were chosen from the hospital's picture archiving and communication system (PACS). Aquilion Multi 64 helical CT was used to perform CT examinations and measurements on patients. Based on CT images, the trajectory L and M for each C1 pedicle were established. Posterior arch height was measured on C1 coronal image. The medullary cavity width along trajectory M was narrower than trajectory L. The medullary cavity width that was less than 3.5 mm was found in 12.5% pedicles along trajectory M and 2.5% along trajectory L. The posterior arch height along trajectory L was significantly higher than that of trajectory M. Posterior arch height that was less than 3.5 mm was found in 74.2% pedicles along trajectory M and only 16.7% along trajectory L. The pedicle length along trajectory L was significantly longer than trajectory M. Trajectory angles for C1 pedicles had an average of 9.08° ± 4.66° along trajectory L and 14.53° ± 4.03° along trajectory M. The Optimal entry point of trajectory L was 5.4 mm medial to trajectory M. Based on our results, this study suggests that C1 pedicle screw trajectory with lateral inclination yielded a good outcome in the treatment of AAI.