Abstract: BACKGROUND: Atlantoaxial dislocation is often facilitated by interlaminar bone grafting. However, there are relatively few reports on the treatment of complex atlantoaxial dislocation with posterior atlantoaxial lateral mass interarticular release and fusion. 
OBJECTIVE: To explore the safety and effectiveness of atlantoaxial dislocation treated by simple posterior atlantoaxial lateral block interarticular release and fusion. 
METHODS: We retrospectively analyzed the clinical data of 30 patients with atlantoaxial dislocation who were treated from January 2017 to July 2021, all of whom suffered from reducible atlantoaxial dislocation. Posterior atlantoaxial lateral mass interarticular release and fusion were performed in all patients. During the surgery, patented instruments were used to release the atlantoaxial lateral mass joint, and posterior screw reduction and fixation were used with bone grafting in the lateral mass joint space. The postoperative follow-up period was 6 to 24 months, mean (13.0±5.4) months. During the follow-up period, cervical MRI was reviewed to observe the decompression of the upper cervical spine. X-ray films and CT scans were reviewed to observe the reduction of the upper cervical spine, as well as the internal fixation for looseness and breakage. CT scans were reviewed to assess interlateral block implant fusion. The Japanese Orthopaedic Association score was used to evaluate the improvement of spinal cord function. The neck disability index and the quality of life scale were used to assess the improvement of daily life function. The atlanto-anterior interspace and atlanto-planar spinal effective space were used to evaluate atlantoaxial repositioning and decompression.  
RESULTS AND CONCLUSION: (1) The surgery of 30 patients went smoothly, and no serious complications such as spinal nerve and vertebral artery injuries occurred during the operation. Postoperative review of cervical MRI showed that the spinal cord compression was lifted. X-ray film and CT showed that the atlanto-anterior gap was significantly reduced; the effective space of atlantoaxial spinal cord was significantly increased, and neurological dysfunctional symptoms were significantly reduced. (2) During the follow-up period, X-ray film and CT showed that the internal fixation was solid; no broken nails or rods occurred, and there was no recurrence of atlantoaxial dislocation. (3) The Japanese Orthopaedic Association scores, neck disability index, and quality of life scores were significantly improved at the last follow-up compared with the preoperative period (P < 0.05). The average improvement rate of Japanese Orthopaedic Association scores at the last follow-up was 73.1%. The average neck disability index was 8.80%. All of the patients had a continuous bone-scalp connection between atlantoaxial lateral block joints to achieve osseous fusion. (4) These findings indicate that the use of simple posterior atlantoaxial lateral block interarticular release and fusion for the treatment of atlantoaxial dislocation can significantly increase the fusion rate and shorten the fusion time.

Key words: atlantoaxial dislocation, atlantoaxial mass joint, release, decompression, fixation, fusion