title: Biomechanical evaluation of a new pedicle screw-based posterior dynamic stabilization device (Awesome Rod System)--a finite element analysis.
abstract: BACKGROUND
  Pedicle-screw-based posterior dynamic stabilization devices are designed to alleviate the rate of accelerated degeneration of the vertebral level adjacent to the level of spinal fusion. A new pedicle-screw-based posterior dynamic stabilization device- the Awesome Dynamic Rod System was designed with curve cuts on the rods to provide flexibility. The current study was conducted to evaluate the biomechanical properties of this new device.
  
  
  METHODS
  Finite element models were developed for the intact spine (INT), the Awesome Dynamic Rod Implanted at L4-L5 (AWE), a traditional rigid rod system implanted at L4-L5 along with an interbody cage (FUS), and the Awesome Dynamic Rod System implanted at L4-L5 along with an interbody cage as an adjunct to fusion procedures and extension of dynamic fixation to L3-L4 (AWEFUS). The models were subjected to axial loads and pure moments and evaluated by a hybrid method on range of motion (ROM)s, disc stresses, pedicle screws stresses, and facet joint contact forces.
  
  
  RESULTS
  FUS sustained the lowest L4-L5 ROM decrement in flexion and torsion. AWE demonstrated the lowest adjacent level ROM increment in all moments except for extension at L3-L4, and AWEFUS showed the greatest ROM increment at L2-L3. AWE demonstrated lowest adjacent segment disc stress in flexion, lateral bending and torsion at L3-L4. AWEFUS showed the highest disc stress increment in flexion, extension, and lateral bending, and the lowest disc stress decrement in torsion at L2-L3. AWE sustained greater adjacent facet joint contact forces than did FUS in extension and lateral bending at L3-L4, and AWEFUS demonstrated the greatest contact forces concentrating at L2-L3.
  
  
  CONCLUSIONS
  The results demonstrate that the Awesome Dynamic Rod System preserved more bridged segment motion than did the traditional rigid rod fixation system except in extension. However, the Awesome Dynamic Rod System bore a greater facet joint contact force in extension. The Awesome Dynamic Rod System did protect the adjacent level of fusion segments, but led to much greater ROM, disc stresses, and facet joint contact forces increasing at the adjacent level of instrumented segments.
authors.affiliation: Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan. cschen@ym.edu.tw.
authors.forename: Chen-Sheng
authors.initials: CS
authors.lastname: Chen
authors.affiliation: Biomedical Research, Mackay Memorial Hospital, Tamshui District, New Taipei City, Taiwan. changhung0812@gmail.com.
authors.forename: Chang-Hung
authors.initials: CH
authors.lastname: Huang
authors.affiliation: Department of Orthopaedic Surgery, Zhong-Xing Branch of Taipei-City Hospital, No. 145, Zhengzhou Rd., Datong Dist., Taipei, 10341, Taiwan. rockwood@nccu.edu.tw.|Institute of Neuroscience, National Chengchi University, Taipei, Taiwan. rockwood@nccu.edu.tw.
authors.forename: Shih-Liang
authors.initials: SL
authors.lastname: Shih
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery; D008159:Lumbar Vertebrae / Q000601:surgery*; D008953:Models, Anatomic; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation*; D013314:Stress, Mechanical; D016474:Weight-Bearing