title: A comparison of the shock-absorbing properties of cervical disc prosthesis bearing materials.
abstract: BACKGROUND
  Cervical arthroplasty offers theoretical advantages over traditional spinal fusion, including elimination of adjacent segment disease and elimination of the risk of pseudoarthrosis formation. Initial studies of cervical arthroplasty have shown promising results, however, the ideal design characteristics for disc replacement constructs have not been determined. The current study seeks to quantify the differences in the shock absorption characteristics of three commonly used materials in cervical disc arthroplasty.
  
  
  METHODS
  Three different nucleus materials, polyurethane (PU), polyethylene (PE) and a titanium-alloy (Ti) were tested in a humidity- and temperature-controlled chamber. Ten of each nucleus type underwent three separate mechanical testing protocols to measure 1) dynamic stiffness, 2) quasi-static stiffness, 3) energy absorption, and 4) energy dissipation. The results were compared using analysis of variance.
  
  
  RESULTS
  PU had the lowest mean dynamic stiffness (435 ± 13 N/mm, P < .0001) and highest energy absorption (19.4 ± 0.1 N/mm, P < .0001) of all three nucleus materials tested. PU was found to have significantly higher energy dissipation (viscous damping ratio 0.017 ± 0,001, P < .0001) than the PE or TI nuclei. PU had the lowest quasi-static stiffness (598 ± 23 N/mm, P < .0001) of the nucleus materials tested. A biphasic response curve was observed for all of the PU nuclei tests.
  
  
  CONCLUSIONS
  Polyurethane absorbs and dissipates more energy and is less stiff than either polyethylene or titanium.
  
  
  METHODS
  Basic Science/Biomechanical Study.
  
  
  CONCLUSIONS
  This study characterizes important differences in biomechanical properties of materials that are currently being used for different cervical disc prostheses.
authors: Disc Dynamics Inc., Eden Prairie, MN.
authors: Michael C
authors: MC
authors: Dahl
authors: Department of Orthopedics, Indiana University School of Medicine, Indianapolis, IN.
authors: Stephen
authors: S
authors: Jacobsen
authors: Medtronic Sofamor Danek, Memphis, TN.
authors: Newton
authors: N
authors: Metcalf
authors: Indiana Spine Group, Indianapolis, IN.
authors: Rick
authors: R
authors: Sasso
authors: Applied Biomechanics Laboratory, University of Washington, Seattle, WA.
authors: Randal P
authors: RP
authors: Ching
keywords: Cervical Disc Arthroplasty; Cervical Spine; Degenerative Disc Disease; Shock Absorption