Value of hyperextension MRI of cervical vertebra in determining decompression therapy after reduction of reducible atlantoaxial dislocation

Objective To determine the value of hyperextension MRI evaluation in determining whether to perform decompression therapy after reduction of reducible atlantoaxial dislocation as well as assess the decompression effect. Methods A retrospective case series study was conducted to analyze 24 patients with atlantoaxial dislocation admitted to Honghui Hospital affiliated to Xi'an Jiaotong University from May 2015 to May 2017. There were 10 males and 14 females, aged 40-74 years, with an average age of 52 years. There were 14 patients with os odontoideum, four patients with odontoid fracture, and six patients with transverse atlantal ligament rupture. Hyperextension MRI was performed to assess spinal cord compression for all patients. Eight patients with anterior spinal cord compression (Group A) underwent posterior atlantoaxial arch decompression plus atlantoaxial internal fixation reduction and bone graft fusion; 16 patients without anterior compression of the spinal cord (Group B) underwent only atlantoaxial internal fixation reduction and bone graft fusion. Intraoperative and postoperative complications were recorded. Spinal cord compression index and improvement rate of spinal cord decompression were evaluated by routine cervical spine MRI. Japanese Orthopedic Association (JOA) score was used to evaluate the clinical effect. Results All patients were followed up for 3-24 months, with an average of 9.3 months. There was no nerve or vertebral artery injury during the operation, and no screw loosening occurred after surgery. The spinal cord compression index (0.37±0.18) in Group A at the last follow-up was significantly lower than that before operation (0.73±0.22) (P<0.05), while the index in Group B (0.19±0.20) at the last follow-up was also lower than that before operation (0.61±0.25) (P<0.05). The improvement rate of spinal cord decompression was 67.11% in Group A and 70.61% in Group B. The final JOA score of Group A was (13.29±3.68)points, which was significantly better than the preoperative JOA [(5.61±2.74)points] (P<0.05). The final JOA score in Group B [(14.13±3.45)points] was also significantly better than the preoperative JOA [(7.32±2.90)points] (P<0.05). Improvement rate of JOA was 57.31% in Group A and 59.91% in Group B. Conclusions Hyperextension MRI of cervical vertebra can effectively judge whether the anterior spinal cord is compressed after reduction of atlantoaxial dislocation. It has important clinical significance for decompression treatment during reduction and internal fixation of reducible atlantoaxial dislocation. At the same time, posterior atlantoaxial arch resection and decompression can effectively relieve the compression of the spinal cord after reduction of atlantoaxial dislocation. Key words: Atlanto-axial joint; Decompression, surgical; Hyperextension reduction