Dynamic cervical flexion/extension atlantodental interval and functional outcome of the Harms technique for posterior C1/2 fixation: A retrospective analysis of 16 atlantoaxial subluxation cases in a tertiary medical center

Abstract

BackgroundThe aim of this study was to assess the relationship between the atlantodental interval (ADI) on dynamic flexion/extension cervical radiographs and functional outcomes of posterior spinal fixation by the Harms technique for atlantoaxial subluxation (AAS). Dynamic flexion/extension on cervical radiographs is a standard assessment for evaluation of C1/2 instability in AAS patients. Most studies focused on postoperative ADI and functional outcome, including pain and fusion rate; only few studies compared dynamic ADI change pre- to post-operatively. Material and methodsRetrospectively, we reviewed the medical records of 16 patients who underwent posterior spinal fixation in our center from 2018 to 2019. We used dynamic cervical flexion/extension radiographs to assess the pre- to postoperative change at 12 months in ADI of flexion (ADIf), ADI of extension (ADIe), ADI between flexion/extension (ADIΔ), C1/2 fusion rate and functional outcomes measured by the modified Japanese Orthopaedic Association scale (mJOA scale). Postoperative CT at 3∼12 months assessed screw positioning on the Gertzbein and Robbins classification. ResultsIn the 16 patients included in this study, ADIf, ADIe and ADIΔ were significantly reduced, from respectively 8.0mm, 5.0mm and 3.0mm preoperatively to 4.6mm, 3.8mm and 0.8mm at 12 months’ follow-up. The fusion rate was 81% and the mJOA score recovery rate was 34.9±14.7%. Although the screw malposition rate was higher than in other studies in C1(10%) and C2(20%), there were no new neurologic deficits or worsening of symptoms at follow-up. ConclusionsThe ADIΔ showed significant reduction, showing that the Harms technique of posterior spinal fixation can effective in maintaining the stability of the atlantoaxial joint and improving functional outcome.