title: Biomechanics of Hybrid Anterior Cervical Fusion and Artificial Disc Replacement in 3-Level Constructs: An In Vitro Investigation.
abstract: BACKGROUND
  The ideal surgical approach for cervical disk disease remains controversial, especially for multilevel cervical disease. The purpose of this study was to investigate the biomechanics of the cervical spine after 3-level hybrid surgery compared with 3-level anterior cervical discectomy and fusion (ACDF).
  
  
  METHODS
  Eighteen human cadaveric spines (C2-T1) were evaluated under displacement-input protocol. After intact testing, a simulated hybrid construct or fusion construct was created between C3 to C6 and tested in the following 3 conditions: 3-level disc plate disc (3DPD), 3-level plate disc plate (3PDP), and 3-level plate (3P).
  
  
  RESULTS
  Compared to intact, almost 65~80% of motion was successfully restricted at C3-C6 fusion levels (p<0.05). 3DPD construct resulted in slight increase at the 3 instrumented levels (p>0.05). 3PDP construct resulted in significant decrease of ROM at C3-C6 levels less than 3P (p<0.05). Both 3DPD and 3PDP caused significant reduction of ROM at the arthrodesis level and produced motion increase at the arthroplasty level. For adjacent levels, 3P resulted in markedly increased contribution of both upper and lower adjacent levels (p<0.05). Significant motion increases lower than 3P were only noted at partly adjacent levels in some conditions for 3DPD and 3PDP (p<0.05).
  
  
  CONCLUSIONS
  ACDF eliminated motion within the construct and greatly increased adjacent motion. Artificial cervical disc replacement normalized motion of its segment and adjacent segments. While hybrid conditions failed to restore normal motion within the construct, they significantly normalized motion in adjacent segments compared with the 3-level ACDF condition. The artificial disc in 3-level constructs has biomechanical advantages compared to fusion in normalizing motion.
authors.affiliation: Department of Mechanical Engineering, Tsinghua University, Beijing, China (mainland).
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Liao
authors.affiliation: Spine Pain Begone, San Antonio, TX, USA.
authors.forename: Guy R
authors.initials: GR
authors.lastname: Fogel
authors.affiliation: Machinery technology development Co. Ltd., Beijing, China (mainland).
authors.forename: Ting
authors.initials: T
authors.lastname: Pu
authors.affiliation: Department of Orthopaedics, Shenzhen Second Hospital, Shenzhen, Guangdong, China (mainland).
authors.forename: Hongsheng
authors.initials: H
authors.lastname: Gu
authors.affiliation: Department of Mechanical Engineering, Tsinghua University, Beijing, China (mainland).
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Liu
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001860:Bone Plates; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000379:methods; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology / Q000601:surgery; D007405:Intervertebral Disc Displacement / Q000503:physiopathology / Q000601:surgery; D008875:Middle Aged; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000379:methods*; D013314:Stress, Mechanical; D059145:Total Disc Replacement / Q000379:methods*; D020798:Two-Hybrid System Techniques