title: Biomechanical Effects of the Geometry of Ball-and-Socket Artificial Disc on Lumbar Spine: A Finite Element Study.
abstract: METHODS
  A three-dimensional finite element model of intact lumbar spine was constructed and four surgical finite element models implanted with ball-and-socket artificial discs with four different radii of curvature were compared.
  
  
  OBJECTIVE
  To investigate biomechanical effects of the curvature of ball-and-socket artificial disc using finite element analysis.
  
  
  BACKGROUND
  Total disc replacement (TDR) has been accepted as an alternative treatment because of its advantages over spinal fusion methods in degenerative disc disease. However, the influence of the curvature of artificial ball-and-socket discs has not been fully understood.
  
  
  METHODS
  Four surgical finite element models with different radii of curvature of ball-and-socket artificial discs were constructed.
  
  
  RESULTS
  The range of motion (ROM) increased with decreasing radius of curvature in extension, flexion, and lateral bending, whereas it increased with increasing radius of curvature in axial torsion. The facet contact force was minimum with the largest radius of curvature in extension, flexion, and lateral bending, whereas it was maximum with the largest radius in axial torsion. It was also affected by the disc placement, more with posterior placement than anterior placement. The stress in L4 cancellous bone increased when the radius of curvature was too large or small.
  
  
  CONCLUSIONS
  The geometry of ball-and-socket artificial disc significantly affects the ROM, facet contact force, and stress in the cancellous bone at the surgical level. The implication is that in performing TDR, the ball-and-socket design may not be ideal, as ROM and facet contact force are sensitive to the disc design, which may be exaggerated by the individual difference of anatomical geometry.
  
  
  METHODS
  N/A.
authors.affiliation: Department of Medical System Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea.
authors.forename: Jisoo
authors.initials: J
authors.lastname: Choi
authors.affiliation: Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Dong-Ah
authors.initials: DA
authors.lastname: Shin
authors.affiliation: Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea.
authors.forename: Sohee
authors.initials: S
authors.lastname: Kim
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology* / Q000601:surgery; D008159:Lumbar Vertebrae / Q000601:surgery*; D008953:Models, Anatomic; D019736:Prostheses and Implants; D016059:Range of Motion, Articular / Q000502:physiology*; D013123:Spinal Fusion / Q000379:methods; D059145:Total Disc Replacement / Q000379:methods; D021801:Zygapophyseal Joint / Q000601:surgery*