Changing Perception but Unaltered Reality: How Effective Is C1-C2 Fixation for Chiari Malformations without Instability?

Abstract

The recently described C1-C2 fixation without foramen magnum decompression (FMD) for the management of Chiari malformations (CMs) has sparked a controversy. C1-C2 fixation has been reported to be more effective than traditional FMD. However, the results after such a procedure have not been as well validated. We assessed the efficacy of C1-C2 distraction and fusion without FMD in patients with CM and without demonstrable atlantoaxial instability. A total of 40 patients with CM had undergone C1-C2 distraction and fusion without FMD. The preoperative and follow-up clinicoradiological data were prospectively compared using the Klekamp neurologic score, visual analog scale, pBC2 index (ventral brainstem compression), and Vaquero index (syringomyelia). Of the 40 patients, 28 (70%) showed improvement in their neurological score and visual analog scale, 8remained in same status, 3 showed deterioration, and 1 died during the follow-up period. The clinical improvement did not correlate with the severity of ventral cervicomedullary compression or the presence of osseous deformities (assimilated C1 arch, platybasia and basilar invagination) despite the reduction in the mean pBC2 index (7.9 vs. 5.9). The syringomyelia had decreased in 51.7%, with a reduction in the Vaquero index at follow-up (0.48 vs. 0.38). The overall results after C1-C2 distraction and fusion for CM without instability were not exceptionally better and appeared to be similar to the outcomes reported with FMD. The neurological improvement seen in some patients had possibly resulted from indirect ventral decompression (due to distraction of C1-C2) rather than the stabilization itself. The presence of bony anomalies such as an assimilated C1 arch, platybasia, basilar invagination, and ventral brainstem compression did not significantly influence the outcomes.