title: Biomechanical comparison of a novel transoral atlantoaxial anchored cage with established fixation technique - a finite element analysis.
abstract: BACKGROUND
  The transoral atlantoaxial reduction plate (TARP) fixation has been introduced to achieve reduction, decompression, fixation and fusion of C1-C2 through a transoral-only approach. However, it may also be associated with potential disadvantages, including dysphagia and load shielding of the bone graft. To prevent potential disadvantages related to TARP fixation, a novel transoral atlantoaxial fusion cage with integrated plate (Cage + Plate) device for stabilization of the C1-C2 segment is designed. The aims of the present study were to compare the biomechanical differences between Cage + Plate device and Cage + TARP device for the treatment of basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD).
  
  
  METHODS
  A detailed, nonlinear finite element model (FEM) of the intact upper cervical spine had been developed and validated. Then a FEM of an unstable BI model treated with Cage + Plate fixation, was compared to that with Cage + TARP fixation. All models were subjected to vertical load with pure moments in flexion, extension, lateral bending and axial rotation. Range of motion (ROM) of C1-C2 segment and maximum von Mises Stress of the C2 endplate and bone graft were quantified for the two devices.
  
  
  RESULTS
  Both devices significantly reduced ROM compared with the intact state. In comparison with the Cage + Plate model, the Cage + TARP model reduced the ROM by 82.5 %, 46.2 %, 10.0 % and 74.3 % in flexion, extension, lateral bending, and axial rotation. The Cage + Plate model showed a higher increase stresses on C2 endplate and bone graft than the Cage + TARP model in all motions.
  
  
  CONCLUSIONS
  Our results indicate that the novel Cage + Plate device may provide lower biomechanical stability than the Cage + TARP device in flexion, extension, and axial rotation, however, it may reduce stress shielding of the bone graft for successful fusion and minimize the risk of postoperative dysphagia. Clinical trials are now required to validate the reproducibility and advantages of our findings using this anchored cage for the treatment of BI with IAAD.
authors.affiliation: Department of Orthopaedics, Wuhan General Hospital of Guangzhou Command of PLA, Wuhan 430070, China. baocheng255@163.com.|Southern Medical University, Guangzhou 510515, China. baocheng255@163.com.
authors.forename: Bao-cheng
authors.initials: BC
authors.lastname: Zhang
authors.affiliation: Institute of Applied Mechanics and Biomedical Engineering, Taiyuan University of Technology, Taiyuan 030024, China. liuhaibo718905@126.com.
authors.forename: Hai-bo
authors.initials: HB
authors.lastname: Liu
authors.affiliation: Department of Orthopaedics, Wuhan General Hospital of Guangzhou Command of PLA, Wuhan 430070, China. xianhua_cai@126.com.|Southern Medical University, Guangzhou 510515, China. xianhua_cai@126.com.
authors.forename: Xian-hua
authors.initials: XH
authors.lastname: Cai
authors.affiliation: Institute of Applied Mechanics and Biomedical Engineering, Taiyuan University of Technology, Taiyuan 030024, China. wangzh@tyut.edu.cn.
authors.forename: Zhi-hua
authors.initials: ZH
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics, Wuhan General Hospital of Guangzhou Command of PLA, Wuhan 430070, China. gkxf79390@sohu.com.
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
authors.affiliation: Department of Orthopaedics, Wuhan General Hospital of Guangzhou Command of PLA, Wuhan 430070, China. kanghuicss@163.com.
authors.forename: Hui
authors.initials: H
authors.lastname: Kang
authors.affiliation: Department of Orthopaedics, Wuhan General Hospital of Guangzhou Command of PLA, Wuhan 430070, China. dana-doctor@hotmail.com.
authors.forename: Ran
authors.initials: R
authors.lastname: Ding
authors.affiliation: The School of Internet of Things, Jiangnan University, Wuxi 214122, China. qingqingchong@126.com.
authors.forename: Xiao-qing
authors.initials: XQ
authors.lastname: Luo
mesh_terms: D001268:Atlanto-Axial Joint / Q000601:surgery*; D020342:Finite Element Analysis; D006801:Humans; D004204:Joint Dislocations / Q000601:surgery*; D019637:Orthopedic Procedures / Q000295:instrumentation* / Q000379:methods