title: Dynamic biomechanical examination of the lumbar spine with implanted total spinal segment replacement (TSSR) utilizing a pendulum testing system.
abstract: BACKGROUND
  Biomechanical investigations of spinal motion preserving implants help in the understanding of their in vivo behavior. In this study, we hypothesized that the lumbar spine with implanted total spinal segment replacement (TSSR) would exhibit decreased dynamic stiffness and more rapid energy absorption compared to native functional spinal units under simulated physiologic motion when tested with the pendulum system.
  
  
  METHODS
  Five unembalmed, frozen human lumbar functional spinal units were tested on the pendulum system with axial compressive loads of 181 N, 282 N, 385 N, and 488 N before and after Flexuspine total spinal segment replacement implantation. Testing in flexion, extension, and lateral bending began by rotating the pendulum to 5°; resulting in unconstrained oscillatory motion. The number of rotations to equilibrium was recorded and bending stiffness (N-m/°) was calculated and compared for each testing mode.
  
  
  RESULTS
  The total spinal segment replacement reached equilibrium with significantly fewer cycles to equilibrium compared to the intact functional spinal unit at all loads in flexion (p<0.011), and at loads of 385 N and 488 N in lateral bending (p<0.020). Mean bending stiffness in flexion, extension, and lateral bending increased with increasing load for both the intact functional spinal unit and total spinal segment replacement constructs (p<0.001), with no significant differences in stiffness between the intact functional spinal unit and total spinal segment replacement in any of the test modes (p>0.18).
  
  
  CONCLUSIONS
  Lumbar functional spinal units with implanted total spinal segment replacement were found to have similar dynamic bending stiffness, but absorbed energy at a more rapid rate than intact functional spinal units during cyclic loading with an unconstrained pendulum system. Although the effects on clinical performance of motion preserving devices is not fully known, these results provide further insight into the biomechanical behavior of this device under approximated physiologic loading conditions.
authors: Department of Orthopaedics, Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, Rhode Island, United States of America. alandanielsmd@gmail.com
authors: Alan H
authors: AH
authors: Daniels
authors: David J
authors: DJ
authors: Paller
authors: Sarath
authors: S
authors: Koruprolu
authors: Mark A
authors: MA
authors: Palumbo
authors: Joseph J
authors: JJ
authors: Crisco
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery*; D008161:Lumbosacral Region / Q000502:physiology* / Q000601:surgery; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D011187:Posture / Q000502:physiology; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013123:Spinal Fusion / Q000379:methods