Preclinical evaluation of a novel anterior non-fusion fixation device for atlantoaxial instability: an in vivo comparison study in a canine model.

PURPOSE: The Anterior Atlantoaxial Non-Fusion Fixation System (AANFS) was a novel motion preservation device for atlantoaxial instability to replace traditional fusion techniques. The purpose of this in vivo study was to evaluate the clinical features and biomechanical properties of this new device in a canine model by comparing it with a conventional method.

METHODS: Eighteen adult male canines were randomly divided into group 1, which received the AANFS replacement, group 2 which received the Harms rigid fixation procedures, and group 3, which served as the control group. Routine follow-up evaluations were performed postoperatively. Specimens were harvested 12 weeks after the operation. Biomechanical tests were conducted to obtain the range of motion (ROM) and neutral zone (NZ) at C1-C2 segment in different groups.

RESULTS: The canines successfully tolerated the entire experimental procedure. No significant differences were found in surgery time, blood loss and recovery time between the AANFS group and the Harms rigid fixation group. Radiological examinations revealed that the position of the implant was good. Biomechanical results showed that, compared with the intact group, the mean ROM and NZ in flexion, extension, lateral bending and rotation were significantly reduced after rigid fixation. However, after the AANFS implantation, ROM and NZ in all directions were similar to those of the intact state.

CONCLUSIONS: This study for the first time provides an animal model for studying non-fusion strategies of upper cervical spine. The AANFS was able to maintain movement function of the atlantoaxial joint and may be an alternative to traditional fusion techniques. These slides can be retrieved under Electronic Supplementary Material.