Atlantoaxial Fixation for Chiari 1 Formation in Pediatric Age-Group Patients: Report of Treatment in 33 Patients.

Abstract

The role of atlantoaxial instability in the pathogenesis of Chiari 1 formation (Chiari formation) in pediatric age-group patients is evaluated. During the period of January 2010 to June 2017, 33 pediatric patients having Chiari formation were treated with atlantoaxial fixation. Twenty-four patients had basilar invagination, and 9 patients had no bone abnormality at the craniovertebral junction. Sixteen patients had syringomyelia, and 9 patients had both basilar invagination and syringomyelia. Considering the type of facetalignment and atlantoaxial instability, the patients were divided into 3 groups. Type 1 dislocation (13 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type 2 dislocation (5 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type 3 dislocation (15 patients) was the absence of demonstrable facet malalignment. Type 2 and 3 atlantoaxial facet instability were labeled as central atlantoaxial dislocation. In 14 patients, dynamic images showed mobile and at least partially reducible vertical 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. All patients had gratifying and sustained clinical improvement. The outcome further confirms the cause-effect relationship of Chiari formation and atlantoaxial instability.