title: Biomechanical analysis of multilevel cervical corpectomy and plate constructs.
abstract: OBJECTIVE
  The authors compared the biomechanical stability of two multilevel cervical constructs involving the placement of equal size anterior cervical plates (ACPs) after decompressive surgery: the first is placed after three-level corpectomy with strut graft and the second after two-level corpectomy and aggressive discectomy with strut graft. In addition, both constructs were evaluated with and without the application of a screw attaching the ACP to the strut graft to determine whether the additional screw enhanced stability in any mode of loading.
  
  
  METHODS
  Nondestructive repeated-measures in vitro flexibility tests were performed in human cadaveric cervical spines. Nonconstraining pure moments of up to 1.5 Nm were applied while recording three-dimensional angular motion stereophotogrammetrically at each level from C4-5 to C7-T1. Nine specimens underwent the three-level corpectomy/strut graft procedure and eight specimens the two-level corpectomy/discectomy strut graft procedure. Failures during testing eliminated two of the former specimens and three of the latter specimens from analysis. The construct applied after the two-level procedure allowed a significantly smaller normalized neutral zone during flexion-extension than the three-level construct (p = 0.04). Normalized elastic zone and range of motion were consistently smaller in the two- than in the three-level construct, but the differences were not significant. Addition of a screw to the strut graft significantly reduced motion in the three-level procedure-treated specimens during flexion and lateral bending but had no effect on two-level corpectomy-treated specimens.
  
  
  CONCLUSIONS
  The construct associated with the two-level corpectomy/discectomy provided better immediate postoperative stability than that associated with the three-level corpectomy. The addition of a screw to the strut graft conferred stability on the three-level construct but not the two-level construct.
authors.affiliation: Division of Neurological Surgery, Spinal Biomechanics Research Laboratory, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013-4496, USA. neuropub@chw.edu
authors.forename: Randall W
authors.initials: RW
authors.lastname: Porter
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.forename: Robert H
authors.initials: RH
authors.lastname: Chamberlain
authors.forename: Sung Chan
authors.initials: SC
authors.lastname: Park
authors.forename: Paul W
authors.initials: PW
authors.lastname: Detwiler
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Apostolides
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000379:methods*