Screw Fixation For Atlantoaxial Instability Research Articles

Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability.

Study DesignCadaveric, observational study.PurposeAtlantoaxial instability (AAI) is characterized by excessive movement at the C1–C2 junction between the atlas and axis. An anterior surgical approach to expose the upper cervical spine for internal fixation and bone grafting has been developed to fix AAI. Currently, no anatomic information exists on the anterior transarticular atlantoaxial screw or screw and plate fixation between C1 and C2 in the Indian population. The objective of this study is to assess the anatomic landmarks of C1–C2 vertebrae: entry point, trajectory, screw length, and safety of the procedure.Overview of LiteratureMethods outlined by Magerl and Harms are the optimal approaches among the dorsal techniques. Contraindications for these techniques include aberrant location of vertebral arteries, fractures of C1–C2 posterior structures. In these cases, anterior transarticular fixation is an alternative. Several available screw insertion trajectories have been reported. Biomechanical studies have demonstrated that adequate rigidity of this fixation is comparable with posterior fusion techniques.MethodsDirect measurements using Vernier calipers and a goniometer were recorded from 30 embalmed human cadavers. The primary parameters measured were the minimum and maximum lateral and posterior angulations of the screw in the sagittal and coronal planes, respectively, and optimum screw length, if it was placed accurately.Results The posterior and lateral angles of screw placement in the coronal and sagittal planes ranged from 16° to 30° (mean±standard deviation [SD], 23.93°±3.93°) and 8° to 17° (mean±SD, 13.3°±2.26°), respectively. The optimum screw length was 25–38 mm (mean±SD, 28.76±3.69 mm).ConclusionsIf the screw was inserted without lateral angulation, the spinal canal or cord could be violated. If a longer screw was inserted with greater posterior angulation, the vertebral artery at the posterior or posterolateral aspect of the C1 superior facet could be violated. Thus, 26° and 30° of lateral and posterior angulations, respectively, are the maximum angles permissible to avoid injury of the vertebral artery and violations of the spinal canal or atlanto-occipital joint.

Unilateral C1 Lateral Mass and C2 Pedicle Screw Fixation for Atlantoaxial Instability in Rheumatoid Arthritis Patients: Comparison with the Bilateral Method.

ObjectiveBilateral C1 lateral mass and C2 pedicle screw fixation (C1LM-C2P) is an ideal technique for correcting atlantoaxial instability (AAI). However, the inevitable situation of vertebral artery injury or unfavorable bone structure may necessitate the use of unilateral C1LM-C2P. This study compares the fusion rates of the C1 lateral mass and C2 pedicle screw in the unilateral and bilateral methods.MethodsOver five years, C1LM-C2P was performed in 25 patients with AAI in our institute. Preoperative studies including cervical X-ray, three-dimensional computed tomography (CT), CT angiogram, and magnetic resonance imaging were performed. To evaluate bony fusion, measurements of the atlanto-dental interval (ADI) and CT scans were performed in the preoperative period, immediate postoperative period, and postoperatively at 1, 3, 6, and 12 months.ResultsUnilateral C1LM-C2P was performed in 11 patients (44%). The need to perform unilateral C1LM-C2P was due to anomalous course of the vertebral artery in eight patients (73%) and severe degenerative arthritis in three patients (27%). The mean ADI in the bilateral group was 2.09 mm in the immediate postoperative period and 1.75 mm in 12-months postoperatively. The mean ADI in the unilateral group was 1.82 mm in the immediate postoperative period and 1.91 mm in 12-months postoperatively. Comparison of ADI measurements showed no significant differences in either group (p=0.893), and the fusion rate was 100% in both groups.ConclusionAlthough bilateral C1LM-C2P is effective for AAI from a biomechanical perspective, unilateral screw fixation is a useful alternative in patients with anatomical variations.

The height for screw index (HSI) predicts the development of C2 nerve dysfunction associated with C1 lateral mass screw fixation for atlantoaxial instability

To propose a new measure, the height for screw index (HSI), as a predictor of C2 nerve dysfunction in patients who have received posterior C1 lateral mass screw (C1LMS) fixation for atlantoaxial instability and to examine whether the HSI scores correlated with the development of C2 nerve dysfunction through retrospective analysis of 104 C1LMS inserted in 52 patients with atlantoaxial instability. The medical records of patients who underwent C1LMS fixation were retrospectively reviewed. C1LMS, 3.5mm in diameter, was inserted for atlantoaxial stabilization. The sagittal plane of the planned C1LMS trajectory was reconstructed from CT images. The HSI was defined as the difference in height between C2 ganglion and its corresponding foramen. C2 nerve function was assessed using a validated visual analog scale questionnaire. Each foramen receiving C1LMS was considered as a single unit and patients were categorized to group 1, HSI ≥4.0mm; group 2, HSI <4.0mm. The mean HSI score was 4.7±0.8mm (range 3.1-6.5mm) with 85 (81.7%) units in group 1, and 19 (18.3%) units in group 2. Fourteen (13.5%, 14/104) units developed C2 nerve dysfunction. C2 nerve dysfunction was reported in 4 units in group 1, and 10 units in group 2, respectively. The percentage of C2 nerve dysfunction was significantly higher in group 2 than that in group 1 (P<0.001, Pearson Chi-square test). The HSI score correlates with the development of C2 nerve dysfunction in patients receiving C1LMS fixation for atlantoaxial instability and may be a useful predictor of C2 nerve dysfunction.

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.

Comparison of Isocentric C-Arm 3-Dimensional Navigation and Conventional Fluoroscopy for C1 Lateral Mass and C2 Pedicle Screw Placement for Atlantoaxial Instability

A retrospective study. The aim of the study was to compare the precision of C1 lateral mass and C2 pedicle (C1LM-C2P) screw fixation for atlantoaxial instability using the isocentric C-arm 3-dimensional (Iso-C 3D) navigation versus conventional fluoroscopy. The Iso-C 3D navigation has been widely used in spinal surgeries in recent years. The advantages of this navigation system compared with conventional fluoroscopy in C1LM-C2P screw fixation for atlantoaxial instability are not known. Twenty-four patients diagnosed with atlantoaxial instability were treated with C1LM-C2P screw fixation in this study. The navigation group included 12 patients and the other 12 patients were in the conventional fluoroscopy group. The clinical and radiographic results were recorded and compared between the 2 groups. Patients were followed up with clinical examination and radiographs at a mean of 10.8 months. There were no significant differences between groups in the mean age, gender, and causes of atlantoaxial instability. Operative time was 130 ± 5.4 minutes in the navigation group versus 145 ± 6.5 minutes in the conventional fluoroscopy group. The mean blood loss in the navigation group was 304.2 ± 47.9 mL relative to 462.5 ± 55.4 mL in the conventional fluoroscopy group. The radiation time was significantly reduced using 3D navigation (47.5 ± 1.5 s vs. 64.0 ± 3.0 s). 95.8% (46/48) of 3D navigated screws and 83.3% (40/48) of fluoroscopy screws had no pedicle perforation. Each patient showed evidence of solid fusion after 6 months on cervical plain radiographies. On comparing the 2 imaging techniques, it was found that using Iso-C 3D navigation can significantly improve the accuracy of screw placement and decrease intraoperative fluoroscopic time and blood loss. This study demonstrates that Iso-C 3D navigation is a safe and effective means of guiding C1LM-C2P screw fixation for atlantoaxial instability.

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.

C1–C2 Transarticular Screw Fixation for Atlantoaxial Instability due to Rheumatoid Arthritis

STUDY DESIGN.: Observational study. Retrospective analysis of prospectively collected data. OBJECTIVE.: The purpose of this article was to report long-term (minimum 7 years) clinical and radiologic outcome of our series of patients with Rheumatoid Arthritis who underwent transarticular screw fixation to treat atlantoaxial subluxation. SUMMARY OF BACKGROUND DATA.: The indications for intervention in patients with atlantoaxial instability are pain, myelopathy, and progressive neurologic deficit. The various treatment options available for these patients are isolated C1-C2 fusion, occipitocervical fusion with or without transoral surgery. Review of current literature suggests that C1-C2 transarticular screw fixation has significant functional benefits, although there is discrepancy in this literature regarding improvement in function following surgery. METHODS.: Myelopathy was assessed using Ranawat myelopathy score and Myelopathy Disability Index. Pain scores were assessed using Visual Analogue Scale. The radiologic imaging was assessed and the following data were extracted; atlanto-dens interval, space available for cord, presence of signal change on T2 weighted image, and fusion rates. RESULTS.: Thirty-seven patients, median age 56, were included in the study. Average duration of neck symptoms was 15.8 months. Average duration of rheumatoid arthritis before surgery was 20.6 years. Preoperative symptoms: suboccipital pain in 26 patients; neck pain, 32; myelopathy, 22; and 5 were asymptomatic. After surgery: suboccipital pain, 2; neck pain, 3; and myelopathy, 10. Ninety percent patients with neck and suboccipital pain improved after surgery in their Visual Analogue pain scores, with all of them having >50% improvement in VAS scores (6.94-2.12 [P < 0.05]).Preoperative Ranawat grade was as follows: grade 1 in 15 patients, grade 2 in 7, and grade 3a in 14, grade 3b in 1.After surgery: grade 1 in 27 patients, grade 2 in 7, grade 3a in 1, and grade 3b in 2. The mean myelopathy score improved after surgery (59.62-32.75, P < 0.05).The space available for the cord was improved in 63%, unchanged in 33%, and worse in 4%.Twenty-seven percent had T2 signal change and 18% had cervicomedullary compression; 97% had bony fusion. BILATERAL SCREWS WERE USED IN 33 PATIENTS AND UNILATERAL SCREWS IN 4 PATIENTS (ABERRANT VERTEBRAL ARTERY).: Computer image guidance was used in 73%. CONCLUSION.: C1-C2 transarticular screw fixation is a safe technique for atlantoaxial subluxation for patients with rheumatoid arthritis. This study clearly demonstrates improvement in Visual Analogue Scale, Ranawat grading and the Myelopathy Disability Index even at long-term follow up.

Efficacy and Durability of the Titanium Mesh Cage Spacer Combined With Transarticular Screw Fixation for Atlantoaxial Instability in Rheumatoid Arthritis Patients

A retrospective study. This retrospective investigation was conducted to determine efficacy and endurance of titanium mesh cage as a strut for interlaminar wiring by comparing with autologous iliac bone graft (AIBG). For patients with atlantoaxial instability (AAI), allograft bone was harvested on an interlaminar mesh cage and transarticular fixation (TAF) was performed. There have been few studies about atlantoaxial fusion rate and advantages for titanium mesh cage from comparison with AIBG in rheumatoid arthritis (RA) patients. Between January 1998 and October 2007, 55 RA patients were surgically treated for AAI. Among them, 34 patients who underwent surgical treatment with TAF and interlaminar wiring using mesh cage packed with allograft, enrolled in this study (group I). For evaluation of bone fusion about mesh cage group, 21 RA patients who underwent TAF and interlaminar wiring with AIBG were also selected (group II). In both groups, radiologic evidence of bone fusion was assessed with measuring atlantodental interval. Patients were strongly encouraged to mobilize by postoperative 1 day with external cervical bracing. The mean follow-up period was 12.3 months (6-36 months). Overall, bone fusion was achieved in 33 patients (97%) in group I. And, this was comparable with 100% of group II. There was no statistical difference in bone fusion rate. During the study period, there were 2 instrument-related complications of screw malposition and cable loosening. The results of this study in which mesh cage was used as an interlaminar spacer, showed immediate rigid fixation and successful bone union. We also could prevent donor site morbidities frequently seen in patients with surgical treatment for AAI.

C1-C2 transarticular screw fixation for atlantoaxial instability: a 6-year experience.

We review a 6-year, single-center experience using the technique of C1-C2 transarticular screw fixation for atlantoaxial instability in 75 consecutive operations. The study group was composed of 43 men and 32 women, with a mean age of 44 years (range, 8-76 yr). Each patient had documented atlantoaxial instability. In 28 patients (37%), atlantoaxial instability was a result of trauma; in 22 patients, (29%), it was a result of rheumatoid arthritis; in 16 patients (21%), it was a result of prior surgery; and in 9 patients (12%), it was a result of congenital abnormalities. All patients underwent stabilization with C1-C2 transfacetal screws and a posterior interspinous construct. Nine patients had unilateral screws placed. Postoperatively, the patients were maintained in a rigid cervical orthosis for a mean of 11 weeks (range, 8-15 wk); five patients were immobilized with halo fixation for a mean of 13 weeks (range, 10-16 wk). The mean follow-up period was 2.4 years (range, 1-5.5 yr). Osseous fusion was documented in 72 patients (96%). There were no hardware failures; however, three patients developed pseudarthrosis. Two superficial wound infections (one at the graft site and one at the cervical incision site) required antibiotic therapy. Four patients had transient suboccipital hypesthesia. No instances of an errant screw, dural laceration, or injury to the vertebral artery, spinal cord, or hypoglossal nerve were noted. C1-C2 transarticular screw fixation supplemented with an interspinous construct yielded a 96% fusion rate, with a low incidence of complications. We attribute our successful outcomes to careful preoperative assessment and meticulous surgical technique.

Point of View: Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability

Point of View: Anatomic Considerations of Anterior Transarticular Screw Fixation for Atlantoaxial Instability