title: The importance of loading the periphery of the vertebral endplate.
abstract: BACKGROUND
  Commercial fusion cages typically provide support in the central region of the endplate, failing to utilize the increased compressive strength around the periphery. This study demonstrates the increase in compressive strength that can be achieved if the bony periphery of the endplate is loaded.
  
  
  METHODS
  Sixteen cadaveric lumbar vertebrae (L1-L5) were randomly divided into two even groups. A different commercial mass produced implant (MPI) was allocated to each group: (I) a Polyether-ether-ketone (PEEK) anterior lumber inter-body fusion (ALIF) MPI; and (II) a titanium ALIF MPI. Uniaxial compression at a displacement rate of 0.5 mm/sec was applied to all vertebrae during two phases: (I) with the allocated MPI situated in the central region of the endplate; (II) with an aluminum plate, designed to load the bony periphery of the endplate. The failure load and mode of failure was recorded.
  
  
  RESULTS
  From phase 1 to phase 2, the failure load increased from 1.1±0.4 to 2.9±1.4 kN for group 1; and from 1.3±1.0 to 3.0±1.9 kN for group 2. The increase in strength from phase 1 to phase 2 was statistically significant for each group (group 1: P<0.01, group 2: P<0.05, pairedt-test). There was no significant difference between the groups in either phase (P>0.05,t-test). The mode of failure in phase 1 was the implant being forced through the endplate for both groups. In phase 2, the mode of failure was either a fracture of the epiphyseal rim or buckling of the side wall of the vertebral body.
  
  
  CONCLUSIONS
  Loading the periphery of the vertebral endplate achieved significant increase in compressive load capacity compared to loading the central region of the endplate. Clinically, this implies that patient-specific implants which load the periphery of the vertebral endplate could decrease the incidence of subsidence and improve surgical outcomes.
authors.affiliation: Orthopaedic Biomechanics Group, Department of Biomedical Science, Faculty of Medicine and Health Science, Macquarie University, NSW, Australia.
authors.forename: Joseph
authors.initials: J
authors.lastname: Cadman
authors.affiliation: University of Florida, FL, USA;; Spinal Health International, 511 Putter Lane, Longboat Key, FL, USA.
authors.forename: Chester
authors.initials: C
authors.lastname: Sutterlin
authors.affiliation: Orthopaedic Biomechanics Group, Department of Biomedical Science, Faculty of Medicine and Health Science, Macquarie University, NSW, Australia.
authors.forename: Danè
authors.initials: D
authors.lastname: Dabirrahmani
authors.affiliation: Orthopaedic Biomechanics Group, Department of Biomedical Science, Faculty of Medicine and Health Science, Macquarie University, NSW, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Appleyard
keywords: Lumbar vertebrae; biomechanical phenomena; spinal fusion