Atlantoaxial subluxation in ankylosing spondylitis patients: radiographic characteristics and surgical treatment

English Keywords:Ankylosing spondylitis  Atlantoaxial subluxation  Radiographic characteristic  Clinical outcome

English Abstract:

  【Abstract】 Objectives: To explore the clinical and radiographic characteristics of atlantoaxial subluxation(AAS) in ankylosing spondylitis(AS) patients and to assess the clinical efficacy of surgical intervention. Methods: The medical records of eight AS patients with AAS who underwent occipitocervical fusion or upper cervical fusion in our hospital between November 2001 and February 2019 were retrospectively reviewed. All patients were male, aged 15-59 years, with an average of 39.9±16.2 years. Three patients presented with preoperative incomplete paraplegia (two presented with Frankel D and one with Frankel C). Preoperative lateral X-rays of the cervical spine showed that all patients presented with AAS, with an average of 10.4±7.0mm (range 2-17mm) in anterior atlantodental interval(AADI), among whom five were with anterior AAS, with an average AADI of 15.2±2.7mm (11-17mm), and the other three patients presented with posterior AAS and odontoid fracture. C0-C2 angle, C1-C2 angle, C2-C7 angle, C2-C7 sagittal vertical axis(SVA), and AADI were measured on lateral X-rays of the cervical spine before surgery, immediately after surgery, and at the final follow-up. The neurological function was assessed by Frankel grading before operation and before discharge, respectively. Paired samples t test was used to compare the preoperative and postoperative radiographic parameters. The surgical complications were recorded. Results: Seven of the eight patients were followed up for 37.9±38.5 months (range, 3-96 months). C0-C2 angle was improved from preoperative 18.9°±16.7° to 22.6°±15.4° immediately after surgery, and it was 20.4°±11.4° at the final follow-up. C1-C2 angle was corrected from preoperative 19.6°±18.7° to 28.5°±10.1° immediately after surgery, and it was 24.6°±8.1° at the final follow-up; C2-C7 angle was improved from preoperative -6.4°±25.2° to 6.6°±19.7° immediately after surgery, and it was 9.0°±18.8° at the final follow-up. C2-C7 SVA was corrected from preoperative 46.0±36.5mm to 39.4±26.4mm immediately after surgery, and it was 39.6±18.9mm at final follow-up. A significant improvement of AADI from preoperative 10.4±7.0mm to 6.4±4.1mm immediately after surgery was observed(P<0.05), and the AADI was 6.9±4.6mm at final follow-up. There was no significant difference between preoperative and postoperative radiographic parameters including C0-C2 angle, C1-C2 angle, C2-C7 angle, and C2-C7 SVA(P>0.05). The neurological functions of the three patients with preoperative incomplete paraplegia were restored to varying degrees after surgery. Two of them improved from Frankel grade D to grade E. The other one was improved from Frankel grade C to grade D. There were no neurological complications, superficial or deep infection, or implant related complications including screw breakage, rod fracture, and screw loosening. Conclusions: AAS in AS patients predominantly manifests as anterior AAS. Favorable clinical outcomes can be obtained by surgical treatment in AS patients with AAS. Resection of the C1 posterior arch and posterior decompression should be performed in patients with neurological compromise. Posterior cervical/cervicothoracic osteotomy is indicated for patients with obvious cervical/cervicothoracic kyphosis.