Understanding that atlantoaxial instability is the cause of Chiari malformation (CM), the author treated 65 patients using atlantoaxial stabilization. The results are analyzed.
Cases of CM treated using atlantoaxial fixation during the period from January 2010 to November 2013 were reviewed and analyzed. Surgery was aimed at segmental arthrodesis.
The author treated 65 patients with CM in the defined study period. Fifty-five patients had associated syringomyelia. Forty-six patients had associated basilar invagination. Thirty-seven patients had both basilar invagination and syringomyelia. Three patients had been treated earlier using foramen magnum decompression and duraplasty. According to the extent of their functional capabilities, patients were divided into 5 clinical grades. On the basis of the type of facetal alignment and atlantoaxial instability, the patients were divided into 3 groups. Type I dislocation (17 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type II dislocation (31 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type III dislocation (17 patients) was the absence of demonstrable facetal malalignment and was labeled as “central” atlantoaxial dislocation. In 18 patients, dynamic images showed vertical, mobile and at-least partially reducible atlantoaxial dislocation. All patients were treated with atlantoaxial plate and screw fixation using techniques described in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not performed in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct. One patient died, and death occurred in the immediate postoperative phase and was related to a vertebral artery injury incurred during the operation. One patient had persistent symptoms. In the rest of the patients there was gratifying clinical improvement. More remarkably, in 7 patients, the symptoms of lower cranial nerve paresis improved. No patient worsened in their neurological function after surgery. Reductions in the size of the syrinx and regression of the CM were observed in 6 of 11 cases in which postoperative MRI was possible. During the follow-up period, there was no delayed worsening of neurological function or symptoms in any patient. Sixty-three patients improved after surgery, and the improvement was sustained during the average follow-up period of 18 months.
On the basis of outcomes in this study, it appears that the pathogenesis of CM with or without associated basilar invagination and/or syringomyelia is primarily related to atlantoaxial instability. The data suggest that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and segmental arthrodesis. Except in cases in which there is assimilation of the atlas, inclusion of the occipital bone is neither indicated nor provides optimum stability. Foramen magnum decompression is not necessary and may be counter-effective in the long run.
Object. The author discusses the successful preliminary experience of treating selected cases of basilar invagination by performing atlantoaxial joint distraction, reduction of the basilar invagination, and direct lateral mass atlantoaxial plate/screw fixation.
Methods. Twenty-two patients with basilar invagination—in which the odontoid process invaginated into the foramen magnum and the tip of the odontoid process was above the Chamberlain, McRae foramen magnum, and Wackenheim clival lines—were selected to undergo surgery. In all patients fixed atlantoaxial dislocations were documented.
The 16 male and six female patients ranged in age from 8 to 50 years. A history of trauma prior to the onset of symptoms was documented in 17 patients. Following surgery, the author observed minimal-to-significant reduction of basilar invagination and alteration in other craniospinal parameters resulting in restoration of alignment of the tip of the odontoid process and the clivus and the entire craniovertebral junction in all patients. In addition to neurological and radiological improvement, preoperative symptoms of torticollis resolved significantly in all patients. The minimum follow-up period was 12 months and the mean was 28 months.
Conclusions. Joint distraction and firm lateral mass fixation in selected cases of basilar invagination is a reasonable surgical treatment for reducing the basilar invagination, restoring craniospinal alignment, and establishing fixation of the atlantoaxial joint.
Occipitocervical fixation: is it necessary?
✓In this report the author describes an alternative technique of atlantoaxial fixation that involves blocking or “jamming” of movements of the atlantoaxial joint. The technique involves forcible impaction of spiked titanium metal spacers and bone grafts within the distracted atlantoaxial facet joints. Between January 2003 and January 2006, four patients underwent this method of fixation at the Department of Neurosurgery at King Edward Memorial Hospital in Mumbai, India. All four patients had posttraumatic mobile and reducible atlantoaxial dislocation. The mean follow-up period was 16 months (range 5–35 months). Successful atlantoaxial stabilization along with ultimate bone fusion was achieved in all patients and was documented on dynamic radiographs. There were no neurological, vascular, or infection-associated complications.
The author concludes that the described method of atlantoaxial fixation provides an alternative treatment strategy. “Joint jamming” as a stand-alone method or in combination with other fixation methods may provide firm stabilization in cases of atlantoaxial dislocation.
The basic surgical steps in the Goel technique of atlantoaxial fixation involve exposure of the atlantoaxial articulation, denuding of the articular cartilage, stuffing of bone graft pieces within the articular cavity, and subsequent instrumentation.
“High-riding” vertebral artery in relationship to the pedicle-facet of C2 has been widely recognized to be a factor that makes insertion of the C2 pedicle-facet screw difficult or impossible. In this video, a technique of exposure and mobilization of the high-riding vertebral artery to permit safe C2 screw insertion is shown. An alternative option in the presence of such a high-riding vertebral artery is to use either C2 laminar or inferior facetal screw insertion.
The video can be found here: https://youtu.be/LjxxINmzph0