C1-C2 Transarticular Screw Fixation Research Articles

Reducible Nonunited Type II Odontoid Fracture with Atlantoaxial Instability: Outcomes of Two Different Fixation Techniques.

Displaced nonunited type II odontoid fracture can result in atlantoaxial instability, causing delayed cervical myelopathy. Both Magerl’s C1-C2 transarticular screw fixation technique and Harms-Goel C1-C2 screw-rod segmental fixation technique are effective techniques to provide stability. This study aimed to demonstrate the results of two surgical fixation techniques for the treatment of reducible nonunited type II odontoid fracture with atlantoaxial instability. Medical records of patients with reducible nonunited type II odontoid fracture hospitalized for spinal fusion between April 2007 and April 2018 were reviewed. For each patient, specific surgical fixation, either Magerl’s C1-C2 transarticular screw fixation technique augmented with supplemental wiring or Harms-Goel C1-C2 screw-rod fixation technique, was performed according to our management protocol. We reported the fusion rate, fusion period, and complications for each technique. Of 21 patients, 10 patients were treated with Magerl’s C1-C2 transarticular screw fixation technique augmented with supplemental wiring, and 11 were treated with Harms-Goel C1-C2 screw-rod fixation technique. The bony fusion rate was 100% in both groups. The mean time to fusion was 69.7 (95%CI 53.1, 86.3) days in Magerl’s C1-C2 transarticular screw fixation technique and 75.2 (95%CI 51.8, 98.6) days in Harms-Goel C1-C2 screw-rod fixation technique. No severe complications were observed in either group. Displaced reducible, nonunited type II odontoid fracture with cervical myelopathy should be treated by surgery. Both fixation techniques promote bony fusion and provide substantial construct stability.

A Clinical Study to Assess the Efficacy of Anterior Transarticular C1-C2 Screw Fixation for Stabilization of AtlantoAxial Instability

Introduction: The upper cervical spine includes the atlas (C1) and Axis (C2). The anatomy of upper twovertebrae is unique from each other. Atlanto-axial articulation is the most unique, mobile segment of spine,which largely depends on ligamentous supports based on integrity of odontoid for its stability. Historically,atlanto-axial subluxation was treated by reduction and fusion of C1-C2 joint. However, High riding vertebralartery precludes the placement of posterior trans-articular screw, which is liable to injury during screwplacement. Socomputed tomography scans can be used to evaluate the risk of “high riding” vertebral arteryduring the management of atlanto-axial subluxation. Hence, anterior trans-articular screw fixation techniqueavoids the course of high riding vertebral artery.Material and Method: Nine patients underwent NCCT cervical spine with 3-D reconstruction and clinicalevaluation of pain was done by recording the VAS score done pre operatively and after surgery.Results: All surgical cohorts underwent anterior C1-C2 fixation with an average follow up for 24 months.All patients were assessed as per fixed protocol of our local hospital guidelines of orthopaedics department.Pain score was clinically evaluated by VAS score before and after surgery yielding 90% excellent result.Conclusion: Anterior Trans-articular C1-C2 screw fixation isa minimally invasive technique with less bloodloss, shorter skins car and faster post-operative recovery. It is an appropriate technique for stabilization ofAtlanto-Axial instabilities.

Minimally invasive percutaneous C1–C2 transarticular screw fixation as a palliative management option in C2 metastases

Bone metastasis in patients with esophageal carcinoma is rare but serious, often resulting in structural complications of the spine such as atlantoaxial instability and C2 metastases. Atlantoaxial instability is usually managed surgically using screw-rod constructs; however, in patients undergoing radiotherapy, surgical wound healing is a concern. We present a technical note involving a terminally ill patient diagnosed with esophageal carcinoma who suffered from a metastatic lytic lesion of C2 and mechanical neck pain. Due to the patient starting palliative radiotherapy, a percutaneous approach and transarticular screws were used to achieve atlantoaxial fixation and minimize the surgical wound while maintaining the midline tension band. Significant clinical improvement was found. Our patient was able to begin palliative radiotherapy within 1 week of surgery, without surgical and wound complications. This report provides unique insight into the utilization of a minimally invasive approach for pain management and stabilization of the cervical spine for oncology patients.

Challenges of Transarticular Screw Fixation in Young Children: Report of Surgical Treatment of a 5-Year-Old Patient's Unstable Os-Odontoideum.

Surgical procedures for atlantoaxial (C1–C2) fusion in young children are relatively uncommon. The purpose of this study was to report on a surgical treatment for a case of atlantoaxial instability caused by os-odontoideum in association with quadriparesis and respiratory paralysis in a 5-year-old girl. We present the patient's history, physical examination, and radiographic findings, describe the surgical treatment and a five year follow-up, and provide a literature review. The instability was treated by halo immobilization, followed by C1–C2 transarticular screw fixation using a computed tomography-based navigation system. At the five year follow-up, the patient had made a complete recovery with solid union. The authors conclude that C1–2 transarticular screw fixation is technically possible as in a case of atlantoaxial instability in a five-year-old child.

Single-stage anterior release and posterior instrumented fusion for irreducible atlantoaxial dislocation with basilar invagination

Background ContextThe options available for treatment of irreducible atlantoaxial dislocation (IAAD) with basilar invagination are odontoidectomy, posterior decompression, and posterior atlantoaxial joint distraction. In 2006, Wang et al. described that most IAAD can be reduced following anterior release of contracted soft tissues. Anterior release may be done by transoral (TO) or retropharyngeal (RP) approach. Posterior instrumented fusion provides stability and helps in achieving further reduction. PurposeThis study aimed to study the neurologic and radiological outcome following treatment of basilar invagination associated with IAAD by anterior release and posterior instrumented fusion. Study DesignA retrospective case series was carried out. Patient SampleThe patient sample comprised 19 patients with IAAD. Outcome MeasurePatients were assessed for neurologic recovery by Benzel modified Japanese Orthopaedic Association (mJOA) score and radiologically by assessing reduction on lateral radiographs and comparing clivus-canal angle (CCA) on preoperative and postoperative computed tomography scan. MethodsNineteen consecutive patients with IAAD were surgically treated. Anterior release was done via TO approach in 12 patients and RP approach in 7. Following anterior release, all patients underwent posterior instrumented fusion. ResultsThis study included 15 men and 4 women with mean follow-up of 18 months. Pathology included occipitalization of atlas in 16 patients, os odontoideum in 2, and missing posterior elements of axis in 1. All patients had cervical myelopathy. Occipitocervical fixation was done in 18 patients and C1–C2 transarticular screw fixation in 1. Fifteen patients had anatomical reduction whereas four had partial reduction. The CCA improved from a mean preoperative angle of 111.47° to mean postoperative angle of 142.84°. The mJOA improved from preoperative mean mJOA of 12.89 to a postoperative mean mJOA of 16.84. Fusion was achieved in all patients. Maceration of posterior wound which healed by daily cleaning and dressing was noted in three patients. Implant breakage on one side was noted in 1 patient at 3 months post operation; however, the patient remained asymptomatic. ConclusionThis series reinforces the safety and efficacy of both TO and RP anterior release for reduction of IAAD. Posterior fixation helps in achieving further reduction and provides stability. Anterior release followed by instrumented posterior fusion is a safe and effective modality of treatment for IAAD associated with basilar invagination.

A Review of Os Odontoideum in Children

Study Background: Os odontoideum is an anomaly of the cervical axis characterized by an independent ossicle of variable size separated from the hypoplastic dens that can present as an incidental radiographic finding to severe neck pain, torticollis, myelopathy, as well as seizures and syncope. Diagnosis is primarily made based on clinical presentation and extensive radiologic evaluation. In this review, we discuss the etiology, treatment, and management of this rare condition in the pediatric population and propose a treatment algorithm. Methods: We performed a comprehensive retrospective review of English literature in PubMed on surgical approaches to treatment and stabilization of Os osontoideum in children. Results: Asymptomatic children, who are diagnosed with Os odontoideum, but lack overt neurologic deficits, are advised to continue radiologic monitoring with lateral flexion-extension X-rays once a year and MRI evaluation once every five years. For symptomatic patients with significant atlantoaxial instability, neurologic deficits, or myelopathy, surgical treatment is recommended. In cases where the atlantoaxial joint is aligned properly without any kyphotic deformities and vertebral arteries abnormalities, transarticular C1-C2 screw fixation should be considered. If these requirements are not met, C1 lateral mass screws with C2 pars/pedicle screws method are advised. The transoral approach, odontoid screw fixation, and minimally invasive techniques are possible alternatives, but have not been studied enough to be considered standard treatments in pediatric population. Conclusions: These recommendations are meant to initiate a “best practices” strategy for treatment of Os odontoideum in children. We anticipate further refinement of these recommendations as new research and reports arise in the field of minimally invasive neurosurgery.

Intraoperative Computed Tomography With an Integrated Navigation System in Stabilization Surgery for Complex Craniovertebral Junction Malformation

This study was designed to report our preliminary experience with stabilization procedures for complex craniovertebral junction malformation (CVJM) using intraoperative computed tomography (iCT) with an integrated neuronavigation system (NNS). To evaluate the workflow, feasibility and clinical outcome of stabilization procedures using iCT image-guided navigation for complex CVJM. The stabilization procedures in CVJM are complex because of the area's intricate geometry and bony structures, its critical relationship to neurovascular structures and the intricate biomechanical issues involved. A sliding gantry 40-slice computed tomography scanner was installed in a preexisting operating room. The images were transferred directly from the scanner to the NNS using an automated registration system. On the basis of the analysis of intraoperative computed tomographic images, 23 cases (11 males, 12 females) with complicated CVJM underwent navigated stabilization procedures to allow more control over screw placement. The age of these patients were 19-52 years (mean: 33.5 y). We performed C1-C2 transarticular screw fixation in 6 patients to produce atlantoaxial arthrodesis with better reliability. Because of a high-riding transverse foramen on at least 1 side of the C2 vertebra and an anomalous vertebral artery position, 7 patients underwent C1 lateral mass and C2 pedicle screw fixation. Ten additional patients were treated with individualized occipitocervical fixation surgery from the hypoplasia of C1 or constraints due to C2 bone structure. In total, 108 screws were inserted into 23 patients using navigational assistance. The screws comprised 20 C1 lateral mass screws, 26 C2, 14 C3, or 4 C4 pedicle screws, 32 occipital screws, and 12 C1-C2 transarticular screws. There were no vascular or neural complications except for pedicle perforations that were detected in 2 (1.9%) patients and were corrected intraoperatively without any persistent nerves or vessel damage. The overall accuracy of the image guidance system was 98.1%. The duration of interruption during the surgical process for the iCT was 8±1.5 minutes. All patients were clinically evaluated using Nurick grade criteria and for neurological deficits 3 months after surgery. Twenty-one patients (91.3%) improved by at least 1 Nurick grade, whereas the grade remained unchanged in 2 (8.7%) patients. Craniovertebral stability and solid bone fusion was achieved in all patients. NNS was found to correlate well with the intraoperative findings, and the recalibration was uneventful in all cases and had an accuracy of 1.8 mm (range, 0.6-2.2 mm). iCT scanning with integrated NNS was found to be both feasible and beneficial in the stabilization procedures for complex CVJM. In this unusual patient population, the technique seemed to be of value for negotiating complex anatomy and for achieving more control over screw placement.

Bilateral C1–C2 Transarticular Screw and C1 Laminar Hook Fixation and Bone Graft Fusion for Reducible Atlantoaxial Dislocation: A Seven-Year Analysis of Outcome

BackgroundBilateral C1-2 transarticular screw and C1 laminar hook fixation was developed on the basis of transarticular screws fixation. The modified technique has showed a better biomechanical stability than established techniques in previous study. However, long-term (minimum follow-up 7 years) outcomes of patients with reducible atlantoaxial dislocation who underwent this modified fixation technique have not still been reported.MethodsA retrospective study was conducted to evaluate the outcome of 36 patients who underwent this modified technique. Myelopathy was assessed using the Ranawat myelopathy score and Myelopathy Disability Index. Pain scores were assessed using Visual Analogue Scale. Radiological imaging was assessed and the following data were extracted: the atlantodental intervals, the space available for cord, presence of spinal cord signal change on T2 weighted image, C1–C2 angle, C2–C7 angle and fusion rates.FindingsAll patients achieved a minimum seven-year follow up. 95% patients with neck and suboccipital pain improved after surgery; in their Visual Analogue pain scores, there was a greater than 50% improvement in their VAS scores with a drop of 5 points on the VAS (P<0.05). 92% of patients improved in the Ranawat myelopathy grade; the Myelopathy Disability Index assessment showed a preoperative mean score of 35.62 with postoperative mean 12.75(P<0.05). There was not any significant atlantoaxial instability at each follow-up time. The space available for cord increased in all patients. Postoperative sagittal kyphosis of the subaxial spine was not observed. After six months after surgery, bone grafts of all patients were fused. No complications related to surgery were found in the period of follow-up.ConclusionsThe long-term outcomes of this case series demonstrate that under the condition of thorough preoperative preparations, bilateral C1–C2 transarticular screw and C1 laminar hook fixation and bone graft fusion is a reliable posterior atlantoaxial fusion technique for reducible atlantoaxial dislocation.

Mid-term results of computer-assisted cervical reconstruction for rheumatoid cervical spines

Study designA retrospective single-center study. Summary and backgroundWe routinely have used C1–C2 transarticular and cervical pedicle screw fixations to reconstruct highly destructed unstable rheumatoid arthritis (RA) cervical lesions. However, there is little data on mid-term results of surgical reconstruction for rheumatoid cervical disorders, particularly, cervical pedicle screw fixation. ObjectivesThe purpose of this study was to evaluate the mid-term surgical results of computer-assisted cervical reconstruction for such lesions. MethodsSeventeen subjects (4 men, 13 women; mean age, 61±9years) with RA cervical lesions who underwent C1–C2 transarticular screw fixation or occipitocervical fixation, with at least 5years follow-up were studied. A frameless, stereotactic, optoelectronic, CT-based image-guidance system, was used for correct screw placement. Variables including the Japanese Orthopaedic Association (JOA) score, Ranawat class, EuroQol (EQ-5D), atlantodental interval, and Ranawat values before, and at 2 and 5years after surgery, were evaluated. Furthermore, screw perforation rates were evaluated. ResultsThe lesions included atlantoaxial subluxation (AAS, n=6), AAS+vertical subluxation (VS, n=7), and AAS+VS+subaxial subluxation (n=4). There was significant neurological improvement at 2years after surgery, as evidenced by the JOA scores, Ranawat class, and the EQ-5D utility weight. However, at 5years after surgery, there was a deterioration of this improvement. The Ranawat values before, and at 2 and 5years after surgery, were not significantly different. Major screw perforation rate was 2.1%. No neural and vascular complications associated with screw insertion were observed. ConclusionsSubjects with rheumatoid cervical lesions who underwent C1–C2 transarticular screw fixation or occipitocervical fixation using a pedicle screw had significantly improved clinical parameters at 2years after surgery. However, there was a deterioration of this improvement at 5years post surgery.

Posterior C1-C2 transarticular screw fixation for atlantoaxial instability assisted by intraoperative 3-dimensional fluoroscopy-based navigation

To assess the feasibility, efficacy and indication of posterior C1-C2 transarticular screw fixation for atlantoaxial instability assisted by intraoperative 3-dimensional fluoroscopy-based navigation. From November 2005 to October 2012, 58 patients with atlantoaxial instability underwent posterior C1-C2 transarticular screw fixation assisted by intraoperative 3-dimensional fluoroscopy-based navigation. Those with excellent atlantoaxial reduction and no need for decompression underwent percutaneously minimally invasive procedures. Operative duration, blood loss volume, reduction of atlantoaxial joints and postoperative neurovascular complications were recorded. Screw positions were studied by postoperative computed tomography (CT) and divided into 3 categories. The follow-up period was at least 3 months. Local symptoms (assessed by visual analogue scale (VAS) score), neurological conditions (Nurick classification) and bone graft fusion were evaluated. Among them, the procedure was either open surgery (n = 51) or percutaneously minimally invasive surgery (n = 7). A total of 111 screws were placed satisfactorily. Five patients underwent only unilateral C1-C2 transarticular screw fixation. No severe complications were encountered. The mean operative duration was 202.2 ± 54.2 minutes and the average volume of blood loss 412.6 ± 281.2 ml. And the values were comparable to those for the traditional fluoroscopy-guided free-hand procedures. No statistical significance existed between open and percutaneously minimally invasive procedures in operative duration, blood loss volume and precision of screw placement. The patients with incompletely reduced C1-C2 dislocation had comparable clinical outcomes with those with complete reduction. After a 3-month follow-up, all of them showed significant improvements of local symptoms. VAS score decreased from 4.5 ± 1.3 preoperatively to 0.7 ± 0.8 postoperatively while the Nurick classification improved from 2.4 ± 1.1 to 0.6 ± 1.0. And bone graft fusion was satisfactory. Posterior C1-C2 transarticular screw fixation for atlantoaxial instability assisted by intraoperative 3-dimensional fluoroscopy-based navigation is both feasible and safe. Combined with minimally invasive techniques, this procedure may achieve greater precision and minimal invasion.

Upper Cervical Fusion in Children with Morquio Syndrome

Paraplegia or death secondary to upper cervical spine instability and spinal cord compression are known consequences of Morquio syndrome. Decompression and fusion of the upper cervical spine are indicated to treat spinal cord compression. The purpose of this study was to report the intermediate to long-term results of upper cervical spine fusion in children with Morquio syndrome. Twenty patients (nine female and eleven male) with Morquio syndrome who underwent upper cervical spine fusion at a mean age of sixty-three months were retrospectively analyzed with use of hospital records. Radiographic and clinical results were reported. The average follow-up period was eight years and ten months. Fusion was achieved in all patients except one; this patient underwent a revision with transarticular C1-C2 screw fixation. Seven patients developed symptomatic instability below the fusion mass that required extension of fusion to lower levels at a mean of ninety-one months after the initial operation. Two patients required decompression and fusion of a site other than the upper cervical spine. Asymptomatic cervicothoracic and thoracolumbar kyphosis was prevalent among our patients. All patients were neurologically stable at the time of the latest follow-up visit. Upper cervical spine fusion provides reliable fusion and a stable neural outcome in patients with Morquio syndrome. However, distal junctional instability is a major problem at long-term follow-up. Kyphotic deformity of the cervicothoracic and thoracolumbar junction may be present in a large number of patients with Morquio syndrome and evaluation for spinal stenosis at these levels should also be considered.

Computer-assisted C1-C2 Transarticular Screw Fixation "Magerl Technique" for Atlantoaxial Instability

Study DesignA retrospective study.PurposeTo evaluate the surgical results of computer-assisted C1-C2 transarticular screw fixation for atlantoaxial instability and the usefulness of the navigation system.Overview of LiteratureWe used a computed tomography (CT)-based computer navigation system in planning and screw insertion in Magerl's procedure, which provides the most rigid atlantoaxial fusion, to avoid risk of vertebral artery (VA) tear by avoiding high-riding VA during screw insertion.MethodsTwenty patients who underwent atlantoaxial fusion under the CT-based navigation system were studied. The mean observation period was 33.5 months. The evaluated items included the existence of VA stenosis by preoperative magnetic resonance angiography, surgical time, blood loss volume, Japanese Orthopaedic Association (JOA) score and Ranawat's pain criteria before surgery and at final follow-up, postoperative screw position evaluated by CT, and bony fusion.ResultsThe mean operation time was 205 minutes, with the mean blood loss volume of 242 ml. The mean JOA score was 11.6 points before surgery and 13.7 at final follow-up. Occipital and/or cervical pain presented before operation was remitted or resolved in all patients. Evaluation of screw insertion by CT revealed correct penetration to atlantoaxial joints, with a perforation rate of 2.6%. There was no complication, including VA tear, and all patients who were followed-up during one year or more after surgery achieved bony fusion. Some subjects who appeared inappropriate for surgery from CT images were assessed as eligible for surgery based on the evaluation results obtained using the navigation system.ConclusionsIt was demonstrated that the CT-based navigation system is an effective support device for Magerl's procedure.

3D-CTA multi-plane measurements and clinical study on anterior C1-C2 transarticular screw fixation

Objective To investigate screw path safety and clinical efficacy assessment of anterior C1-C2 transarticular screw fixation.Methods 21 cases of traumatic atlantoaxial instability were treated by anterior C1-C2 transarticular screw fixation and followed up,After operation,X-ray and CTA are examed.With the application of 3D-CTA and the AW three-dimensional measurement software,the measurement of the angle of the screw placement and the distance between the screw and the vertebral artery as well as spinal canal at different plane is accessible and used for statistical analysis.Results All the cases with the placement of the cancellous bone screw of which the length is froml9 to 30 mm and diameter is 3.5 mm with the lateral angulation to the sagittal plane ranged from 9 ° to 22 °and the posterior angulation to the coronal plane from 12° to 29° had no trauma on vertebral artery and cervical cord during their cervical operations;20 cases were followed up for about 5 months to 9 years with an average of 20 months.Screw position after operation review showed well with no loosening or breakage and Atlantoaxial synostosis rate was 95％.The clinical symptoms were improved to different levels and patients recovered well.The minimum distance between the screw and the vertebral artery is located inside the plane of transverse foramen of atlas with an average of 5.71 mm(2.2-10.2 mm).The minimum distance between the screw and the spinal canal is located outside the plane of transverse foramen of atlas with an average of 7.36 mm(3.8-13.2 mm).Conclusion Our Research have indicated that anterior C1-C2 transarticular screw fixation is safe and effective. Key words: Atlantoaxial; Anterior path; Transarticular screw fixation; Angiography; Vertebral artery

Biomechanical Evaluations of Various C1-C2 Posterior Fixation Techniques

A biomechanical in vitro study using human cadaveric spine. To compare the biomechanical stability of pedicle screws versus various established posterior atlantoaxial fixations used to manage atlantoaxial instability. Rigid screw fixation of the atlantoaxial complex provides immediate stability and excellent fusion success though has a high risk of neurovascular complications. Some spine surgeons thus insert shorter C2 pedicle or pars/isthmus screws as alternatives to minimize the latter risks. The biomechanical consequences of short pedicle screw fixation remain unclear, however. Seven human cadaveric cervical spines with the occiput attached (C0-C3) had neutral zone (NZ) and range of motion (ROM) evaluated in three modes of loading. Specimens were tested in the following sequence: initially (1) the intact specimens were tested, after destabilization of C1-C2, then the specimens underwent (2) C1 lateral mass and C2 short pedicle screw fixation (PS-S), (3) C1 lateral mass and C2 long pedicle screw fixation (PS-L), (4) C1 lateral mass and C2 intralaminar screw fixation (ILS), (5) Sonntag's modified Gallie fixation (MG) and (6) C1-C2 transarticular screw fixation with posterior wiring (TAS 1 MG). (7) The destabilized spine was also tested. All instrumented groups were significantly stiffer in NZ and ROM than the intact spines, except in lateral bending, which was statistically significantly increased in the TAS 1 MG group. The MG group's NZ and ROM values were statistically significantly weaker than those of the PS-S, PS-L, and the ROM values of the TAS 1 MG groups. The ILS group's NZ values were higher than those of the TAS 1 MG group and for ROM, than that of the PS-S and PS-L groups. In flexion, the NZ and ROM values of the TAS 1 MG group were significantly less than those of the PS-S, PS-L, ILS, and MG groups. In axial rotation, the NZ and ROM values of the MG group were statistically significantly higher than those of the PS-S, PS-L, ISL and TAS 1 MG groups. The TAS 1 MG procedures provided the highest stability. The MG method alone may not be adequate for atlantoaxial arthrodesis, because it does not provide sufficient stability in lateral bending and rotation modes. The C2 pedicle screw and C2 ILS techniques are biomechanically less stable than the TAS 1 MG. In the C1 lateral mass-C2 pedicle screw fixation, the use of a short pedicle screw may be an alternative when other screw fixation techniques are not feasible.

Trans-Articular C1-C2 Fixation: Results Of Twenty-Nine Patients

Twentynine patients having atlanto-axial instability were treated by trans-articular C1-C2 screw fixation .there were twenty one male and female patients with average age of 40.7 years( range, 16 - 56 ). There were eighteen cases of ligamentous atlanto- axial instability, five cases of C2 fracture, five patients with odontoid fracture and a case of non-union of odontoid. Patients were operated between 1-2 weeks of hospitalization. The follow-up averaged 43 months (range 24-60). Fusion occurred in 90% of the patients with good results in 86 % patients. Screw malpostioning, vertebral artery injury, and guide wire breakage were the complications observed during the study.This study establishes the efficacy of trans-articular screw fixation in these highly unstable injuries of cervical spine.

Bilateral Atlantoaxial Transarticular Screws and Atlas Laminar Hooks Fixation for Pediatric Atlantoaxial Instability

An atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks was used in 5 pediatric patients, who were then followed up for 12 to 17 months to evaluate the technique. To describe a modified posterior C1-C2 fixation technique and preliminary clinical and radiographic results in 5 pediatric patients. Conventional posterior atlantoaxial fixations, such as Gallie and Brooks techniques, are frequently associated with high rates of pseudarthrosis and implant failure. The C1-C2 transarticular screw fixation has been shown to be effective in treatment of pediatric atlantoaxial instability, as well as adult atlantoaxial instability; however, this 2-point fixation merely stabilizes the atlantoaxial motion segment laterally. A 3-point fixation, composed with bilateral C1-C2 transarticular screws and C1 laminar hooks, has been developed. Five patients with atlantoaxial instability, including 4 males and 1 female, aged 6 to 17 (average 10) years, underwent atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks during a 2-year period. The surgical technique and treatment procedures were intensively reviewed, and clinical symptoms and imaging appearance were retrospectively evaluated. Clinical follow-ups were obtained for an average of 14.4 (range: 12-17) months. The clinical and radiologic follow-up indicated a stable arthrodesis and offered clinical relief from symptoms for all patients. No neural or vascular impairment related to this technique was observed. Fixation of the atlantoaxial articulation using bilateral C1-C2 transarticular screws and C1 laminar hooks appears to be a reliable technique for treatment of pediatric atlantoaxial instability.

Anterolateral C1—C2 Transarticular Fixation for Atlantoaxial Arthrodesis

An alternative route must be used for atlantoaxial arthrodesis to avoid the risks of transoral route or when posterior approaches are contraindicated. To assess relevant quantitative anatomic parameters for C1-C2 anterolateral transarticular fixation and to demonstrate the nuances of an anterolateral approach to the upper cervical spine. Five cadaveric necks were dissected bilaterally to demonstrate anatomic landmarks and surgical technique. The C2 pars interarticularis was used as the entry for inserting screws toward the C1 lateral mass. Ten computed tomography scans were analyzed to quantify working area and optimal angles of approach. The medial surface of sternocleidomastoid muscle was dissected extensively but not divided. The C2 transverse process was a landmark for guiding dissection posterior to the carotid sheath. In all specimens, the gray ramus communicans from the superior cervical ganglion to the C2 nerve was a landmark for locating the C2 pars. Slightly below that branch, the longus capitis muscle could be displaced medially to reach the C2 pars. The ideal angles for screw placement were 22.9 +/- 5.7 degrees medial to the sagittal plane and 25.3 +/- 7.4 degrees posterior to the coronal plane. The mean working area was 71.2 mm (range, 49-103 mm). We propose a new anterolateral stabilization technique for atlantoaxial instability based on less traumatic dissection of the upper cervical region, different instrumentation, and guidance by reliable landmarks. For anterolateral transarticular C1-C2 screw fixation, the gray ramus communicans to the C2 nerve is a reliable landmark for locating the entry for a screw on the C2 pars.

Study of the Anatomical Variations of Vertebral Artery in C2 Vertebra With Magnetic Resonance Imaging and Its Application in the C1–C2 Transarticular Screw Fixation

Use of magnetic resonance imaging (MRI) with Constructive Interference in Steady State (CISS) sequence and isometric voxels to demonstrate the anatomic variations of vertebral artery in C2 vertebra. To determine the transarticular screw trajectory on CISS MRI and to identify patients with anatomic variations of vertebral artery in C2 vertebra. Atlantoaxial transarticular screw fixation has been reported to be biomechanically superior to other posterior techniques for atlantoaxial arthrodesis. Vertebral artery injury can be associated with catastrophic sequelae. Anatomic variation of vertebral artery is well recognized and computed tomography scan is the traditional preoperative assessment. However, no report has evaluated the use of MRI in preoperative assessment for the screw trajectories and the anatomic variation of vertebral artery. The 3-dimensional (3D) CISS MRI with isometric voxels was performed in 30 local Chinese patients. The 3D reconstruction images were created to determine the proposed screw trajectories and their relationship with the vertebral arteries. In 12 patients (40%), the vertebral arteries were lying within the screw trajectories prohibiting transarticular screw fixation on at least one side. Bilateral variations with high risk of vertebral artery injuries were found in 6 patients. The remaining 6 patients had unilateral variations prohibiting the insertion of transarticular screws on one side. The 3D CISS MRI with isometric voxels is a safe and simple imaging technique to outline the vertebral arteries in C2. Reconstruction images are easily created and undistorted. It is one of the useful imaging in preoperative planning of transarticular screw fixation and determination of anatomy of vertebral artery.

Clinical and radiological Comparison of treatment of atlantoaxial instability by posterior C1–C2 transarticular screw fixation or C1 lateral mass-C2 pedicle screw fixation

We compared the clinical and radiological results of posterior atlantoaxial fixation surgery using transarticular screws to those using a polyaxial screw–rod system in 55 patients with symptomatic atlantoaxial instability. Patients underwent posterior C1–C2 fixation: 28 patients (group 1) underwent C1–C2 transarticular screw fixation and 27 patients (group 2) underwent C1 lateral mass–C2 pedicle screw fixation. Patients were followed-up for at least 24 months. The clinical and radiological results were evaluated in the early postoperative period and at 3, 6, 12 and 24 months after surgery. Long-term postoperative stability and bone fusion were examined. After surgery, 93% of patients in group 1 and 96% of patients in group 2 were free of neck pain. The solid fusion rates were 82% for group 1 patients and 96% for group 2 patients at 12 months ( p < 0.092). In group 1, three patients showed fibrous union. Four patients had hardware failure due to a screw malposition (one in group 1) and pseudoarthrodesis (two in group 1 and one in group 2). One patient in group 1 had cerebrospinal fluid leakage. One patient in group 2 had occipital neuralgia. One vertebral artery injury occurred during the screw placement in group 1 and another in group 2 during the muscle dissection. C1–C2 transarticular screw fixation and C1 lateral mass–C2 pedicle screw fixation both produced excellent results for stabilization of the atlantoaxial complex, but the radiological outcome tended to be superior in C1 lateral mass–C2 pedicle screw fixation.

Biomechanical Analysis Comparing Three C1–C2 Transarticular Screw Salvaging Fixation Techniques

This is an in vitro biomechanical study. To compare the biomechanical stability of the 3 C1-C2 transarticular screw salvaging fixation techniques. Stabilization of the atlantoaxial complex is a challenging procedure because of its complicated anatomy. Many posterior stabilization techniques of the atlantoaxial complex have been developed with C1-C2 transarticular screw fixation been the current gold standard. The drawback of using the transarticular screws is that it has a potential risk of vertebral artery injury due to a high riding transverse foramen of C2 vertebra, and screw malposition. In such cases, it is not recommended to proceed with inserting the contralateral transarticular screw and the surgeon should find an alternative to fix the contralateral side. Many studies are available comparing different atlantoaxial stabilization techniques, but none of them compared the techniques to fix the contralateral side while using the transarticular screw on one side. The current options are C1 lateral mass screw and short C2 pedicle screw or C1 lateral mass screw and C2 intralaminar screw, or C1-C2 sublaminar wire. Nine fresh human cervical spines with intact ligaments (C0-C4) were subjected to pure moments in the 6 loading directions. The resulting spatial orientations of the vertebrae were recorded using an Optotrak 3-dimensional Motion Measurement System. Measurements were made sequentially for the intact spine after creating type II odontoid fracture and after stabilization with unilateral transarticular screw placement across C1-C2 (TS) supplemented with 1 of the 3 transarticular salvaging techniques on the contralateral side; C1 lateral mass screw and C2 pedicle screw (TS+C1LMS+C2PS), C1 lateral mass and C2 intralaminar screw (TS+C1LMS+C2ILS), or sublaminar wire (TS + wire). The data indicated that all the 3 stabilization techniques significantly decreased motion when compared to intact in all the loading cases (left/right lateral bending, left/right axial rotation, flexion) except extension. All the 3 instrumented specimens were equally stable in extension/flexion and lateral bending modes. TS+C1LMS+C2PS was equivalent to TS+C1LMS+C2ILS (P > 0.05) and superior to TS + wire in axial rotation (P < 0.05). Also, TS+C1LMS+C2ILS was superior to TS + wire in axial rotation (P < 0.05). Fixation of atlantoaxial complex using unilateral transarticular screw supplemented with contralateral C1 lateral mass and C2 intralaminar screws is biomechanically equivalent to C1 lateral mass and C2 pedicle screws and both are biomechanically superior to C1-C2 sublaminar wire in axial rotation.