title: [Biomechanical study on the effect of the length of cervical anterior fusion on adjacent levels].
abstract: OBJECTIVE
  To study the effect of length of cervical anterior fusion on adjacent levels by Biomechanical test.
  
  
  METHODS
  Six fresh-frozen human cervical specimens were used in this study. The specimens were tested in flexion, extension, bending and rotation on a spine 3D test system. The specimens were tested intact and then underwent a single-level anterior cervical discectomy and fusion (ACDF) at the C4-5 first, a double-level fusion at the C4-6, and finally extended to triple-level at the C4-7, Based on a hybrid test method. Changes in overall range of motion (ROM), segmental motion and facet joints pressure during flexion, extension, bending and rotation were measured and statistically analyzed.
  
  
  RESULTS
  The overall ROM of the entire spinal construct decreased progressively as the single-level fixation extending to 2-level and 3-level (P < 0.05). A progressive increase in ROM above (C3-4) the fused motion segment units (MSUs) was found during flexion, extension and bending (P < 0.05). In bending and extension, a same result was recorded on the average pressure and max pressure of C3-4 facet joints (P < 0.05).
  
  
  CONCLUSIONS
  This study has demonstrated that the biomechanics at adjacent levels to a cervical spine fusion are altered and that there was progressively increased adjacent segment motion and stress as a single-level ACDF extended to a 3-level fusion, which might lead to the acceleration of adjacent segment degeneration.
authors.affiliation: Department of Orthopaedics, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, China.
authors.forename: Jincai
authors.initials: J
authors.lastname: Yang
authors.affiliation: Email: spinesurgeon@163.com.
authors.forename: Yong
authors.initials: Y
authors.lastname: Hai
authors.forename: Chuan
authors.initials: C
authors.lastname: Pang
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Dan
authors.initials: D
authors.lastname: Zu
authors.forename: Gang
authors.initials: G
authors.lastname: Zhu
authors.forename: Xuguang
authors.initials: X
authors.lastname: Xia
authors.forename: Baoqing
authors.initials: B
authors.lastname: Pei
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D002574:Cervical Vertebrae / Q000601:surgery*; D017586:Diskectomy / Q000379:methods; D006801:Humans; D016059:Range of Motion, Articular; D012399:Rotation; D013123:Spinal Fusion / Q000379:methods*