title: Contributions of flexion-extension cyclic loads to the lumbar spinal segment stability following different discectomy procedures.
abstract: METHODS
  An in vitro biomechanical cadaveric study. OBJECTIVES To elucidate the effect of flexion-extension cyclic loads on the motion behavior of lumbar spine after different discectomies.
  
  
  BACKGROUND
  Biomechanical cadaveric studies to evaluate the effect of discectomy have been performed and have indicated the relevance between the volume of removed disc materials and increase of motion in affected intervertebral disc. However, there are no biomechanical studies to investigate the motion behavior of injured intervertebral disc after cyclic loads.
  
  
  METHODS
  Twenty-eight lumbar functional spinal units were randomized into fenestration, annulotomy, limited discectomy, and radical discectomy groups. Pure bending moments were applied to simulate various loading modes and determine the resulting displacements before and after surgery, and after cyclic loads of 1,000, 5,000, and 10,000 cycles at a frequency of 0.5 Hz and a force of +/-3.0 Nm. Change of range of motion (ROM) was compared among each group.
  
  
  RESULTS
  Following surgery, in the radical discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending. On the other hand, during cyclic loads up to 10,000 cycles, in the limited discectomy group, the relative change of ROM mostly increased in all motion directions except right lateral bending.
  
  
  CONCLUSIONS
  These results demonstrate that the effect of cyclic loads after discectomy may increase ROM, leading to spinal instability even if the increase in ROM does not occur immediately after surgery for the minimum removal of nucleus pulposus case. Clinically, this may underscore the importance of postoperative lumbar support.
authors.affiliation: Department of Orthopaedic Surgery, Miyazaki Medical College, Miyazaki, Japan. hiroshik@post1.miyazaki-med.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kuroki
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Goel
authors.forename: Scott A
authors.initials: SA
authors.lastname: Holekamp
authors.forename: Nabil A
authors.initials: NA
authors.lastname: Ebraheim
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Kubo
authors.forename: Naoya
authors.initials: N
authors.lastname: Tajima
mesh_terms: D001696:Biomechanical Phenomena; D017586:Diskectomy / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*