title: Biomechanical studies of a dynamized anterior thoracolumbar implant.
abstract: METHODS
  An in vitro investigation into the biomechanical properties of a dynamized anterolateral compression implant that allows controlled subsidence.
  
  
  OBJECTIVE
  To determine the extent to which both modes of the anterolateral compression implant (controlled collapsing and rigid) are able to reestablish the stability of the lumbar spine after L4 corpectomy.
  
  
  BACKGROUND
  Over time, anterior and posterior spinal implants have been associated with progressive angulation, and occasionally implant failure and breakage. To circumvent this occurrence and provide better graft loading, dynamized or collapsing devices for clinical use have been developed.
  
  
  METHODS
  Eight fresh calf spines (L1-L6) were placed in a biomechanical testing frame. Pure moments of 6 Nm were loaded onto the intact spine in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. A total L4 corpectomy then was performed, and the defect grafted with a wooden dowel. Loading was repeated after the specimens were stabilized using the two modes of the anterolateral compression implant in succession.
  
  
  RESULTS
  The results showed that both modes of the implant (the rigid mode in particular) restore the stiffness of the unstable spine to normal levels of flexion, extension, and right and left lateral bending, even to levels exceeding normal. These devices, however, fall short of achieving normal stability in right and left axial rotation.
  
  
  CONCLUSIONS
  In the cadaveric calf spine after L4 corpectomy, restoration of stability with a dynamized anterior spinal implant is possible in flexion, extension, and right and left lateral bending, but not in axial rotation.
authors.affiliation: Division of Neurosurgery, University of Iowa, Iowa City, USA. patrick-hitchon@uiowa.edu
authors.forename: P W
authors.initials: PW
authors.lastname: Hitchon
authors.forename: V K
authors.initials: VK
authors.lastname: Goel
authors.forename: T
authors.initials: T
authors.lastname: Rogge
authors.forename: N M
authors.initials: NM
authors.lastname: Grosland
authors.forename: K
authors.initials: K
authors.lastname: Sairyo
authors.forename: J
authors.initials: J
authors.lastname: Torner
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002417:Cattle; D008161:Lumbosacral Region; D019736:Prostheses and Implants; D013131:Spine / Q000601:surgery*