Atlantoaxial Fixation for Treatment of Chiari Formation and Syringomyelia with No Craniovertebral Bone Anomaly: Report of an Experience with 57 Cases

Abstract

Aim: In this paper we evaluate the role of atlantoaxial instability in the pathogenesis of Chiari formation type I and the role of atlantoaxial stabilization for treatment of this condition in cases with no obvious bone malformation in the region of the craniovertebral junction. Materials, Methods and Results: During the period from January 2010 to July 2016, we identified 57 cases of Chiari formation where there was no bone malformation or evidence of craniovertebral junction instability that could be diagnosed on the basis of an abnormal increase in the atlantodental interval on dynamic imaging. Forty-eight of these patients had syringomyelia. The average duration of follow-up was 42 months. There were 30 males and 27 females in the series. The ages of the patients ranged from 4 to 57 years. The Japanese Orthopaedic Association (JOA), visual analogue scale (VAS) and Goel clinical grading systems were used to assess the patients’ clinical status. Atlantoaxial instability was diagnosed on the basis of vertical mobility of the odontoid process on dynamic radiographs, facetal malalignment on imaging or direct bone handling during the surgical procedure. Surgical treatment was achieved using atlantoaxial fixation. Foramen magnum decompression or syrinx manipulation was not done. All patients had immediate postoperative and sustained clinical symptomatic recovery. A reduction in the size of the syrinx was observed in ten patients and regression of tonsillar herniation was observed in 12 of 23 cases in which postoperative magnetic resonance imaging (MRI) was possible. Conclusion: Atlantoaxial instability is the prime factor in the genesis of Chiari formation even when there is no bone abnormality in the craniovertebral junction.