Computer-assisted Magerl's transarticular screw fixation for atlantoaxial subluxation

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

STUDY DESIGN

A retrospective study.

PURPOSE

To evaluate the surgical results of computer-assisted C1-C2 transarticular screw fixation for atlantoaxial instability and the usefulness of the navigation system.

OVERVIEW OF LITERATURE

We 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.

METHODS

Twenty 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.

RESULTS

The 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.

CONCLUSIONS

It was demonstrated that the CT-based navigation system is an effective support device for Magerl's procedure.

Intraoperative vertebral artery angiography to guide c1-2 transarticular screw fixation in a patient with athetoid cerebral palsy

We present a case of an athetoid cerebral palsy with quadriparesis caused by kyphotic deformity of the cervical spine, severe spinal stenosis at the cervicomedullary junction, and atlantoaxial instability. The patient improved after the first surgery, which included a C1 total laminectomy and C-arm guided righ side unilateral C1-2 transarticular screw fixation. C1-2 fixation was not performed on the other side because of an aberrant and dominant vertebral artery (VA). Eight months after the first operation, the patient required revision surgery for persistent neck pain and screw malposition. We used intraoperative VA angiography with simultaneous fluoroscopy for precise image guidance during bilateral C1-2 transarticular screw fixation. Intraoperative VA angiography allowed the accurate insertion of screws, and can therefore be used to avoid VA injury during C1-2 transarticular screw fixation in comorbid patients with atlantoaxial deformities.

Transarticular screw and C1 hook fixation for os odontoideum with atlantoaxial dislocation

OBJECTIVE

To introduce a fixation device composed of C1-2 transarticular (TA) screws and C1 hooks and explore its indication and clinical outcome for os odontoideum with atlantoaxial dislocation (AAD).

METHODS

From January 2004 to December 2008, 12 patients with os odontoideum (5 men and 7 women, average age 37.7 years [range 14-62 years]) were treated in the authors' hospital. All patients had AAD with local symptoms, and 10 had myelopathy. All patients underwent a posterior atlantoaxial fixation with C1-2 TA screws and C1 hooks. Clinical and radiographic analyses were performed at 3, 6, and 12 months postoperatively and annually thereafter.

RESULTS

The follow-up period was 12-66 months (average follow-up period 35.5 months). No neurologic or vascular complications occurred in these cases, and the device was placed well with no loosening or breakage. Plain radiographs and three-dimensional reconstruction of computed tomography (CT) images revealed solid bony fusion with a good alignment of C1 and C2 at 3 months postoperatively. No hardware failure, pseudarthrosis, or instability was noted during the follow-up period. All patients had relief of pain within 3 months, and neurologic symptoms were substantially improved.

CONCLUSIONS

When appropriate patients are selected, C1-2 TA screws combined with C1 hooks can be used to treat os odontoideum with AAD effectively with a relatively simple procedure resulting in excellent biomechanical strength and high bone fusion rate. Preoperative planning is crucial for the management of os odontoideum with AAD.

Stereotactic atlantoaxial transarticular screw fixation

Atlantoaxial stabilisation can be performed using a variety of surgical techniques. Developments in spinal instrumentation and stereotactic technology have been incorporated into these procedures. We have recently adopted frameless stereotaxy to assist in such operations. A retrospective study of patients treated by the authors and using frameless stereotaxy from 2001 to 2002 was performed. Each patient underwent pre-operative fine-cut CT in the position of fixation. Using these images, screw trajectory was planned. Stereotaxis and fluoroscopy was utilised during fixation. A post-operative CT was performed. There were nine patients. Bilateral screw placement was achieved in eight. In the remaining case stereotactic planning predicted the single screw fixation. There were no post-operative complications. Post-operative CT showed screw placement corresponding to the planned trajectory in all 17 screws. Stabilisation was achieved in all. Stereotactic atlantoaxial screw fixation is an accessible, safe and accurate method for the management of C1-2 instability.

Anatomic relationship of the internal carotid artery to the C1 vertebra: A case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas

STUDY DESIGN

A case of internal carotid artery impingement by the tip of a well-positioned C1-C2 transarticular screw is presented along with a pilot study involving radiologic and anatomic evaluation of human cadaveric specimens.

OBJECTIVE

To raise awareness that the internal carotid artery may be in close proximity to the anterior aspect of the atlas and at risk of injury during placement of C1-C2 transarticular screws or C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

To our knowledge, no cases of internal carotid artery injury or impingement have been reported with screw fixation of the atlas.

METHODS

A case of internal carotid artery impingement by a C1-C2 transarticular screw is presented. The C1-C2 rotation appeared to place the internal carotid artery in the path of the screw, prompting a pilot study. Three fresh-frozen human cadaveric head and neck specimens were fixed in different degrees of rotation. Thin-section computed tomography of the specimens was obtained in the plane of the atlas. The frozen specimens were sectioned in the same plane as the computed tomography images. Measurements were taken to assess the location of the internal carotid artery relative to the anterior aspect of the atlas.

RESULTS

Cervical rotation does not have a predictable effect on the location of the internal carotid artery. Medial angulation of a screw placed in the lateral mass of C1 appears to increase the margin of safety for the internal carotid artery. The internal carotid artery varies in location and may be within 1 mm of the ideal exit point of a bicortical transarticular screw or a C1 lateral mass screw.

CONCLUSIONS

The internal carotid artery is at risk during bicortical screw fixation of the atlas. We recommend a contrast-enhanced computed tomography to assess the location of the internal carotid artery before screw fixation of the atlas.