title: Axial rotation mechanics in a cadaveric lumbar spine model: a biomechanical analysis.
abstract: BACKGROUND
  Postoperative patient motions are difficult to directly control. Very slow quasistatic motions are intuitively believed to be safer for patients, compared with fast dynamic motions, because the torque on the spine is reduced. Therefore, the outcomes of varying axial rotation (AR) angular loading rate during in vitro testing could expand the understanding of the dynamic behavior and spine response.
  
  
  OBJECTIVE
  To observe the effects of the loading rate in AR mechanics of lumbar cadaveric spines via in vitro biomechanical testing.
  
  
  METHODS
  An in vitro biomechanical study in lumbar cadaveric spines.
  
  
  METHODS
  Fifteen lumbar cadaveric segments (L1-S1) were tested with varying loading frequencies of AR. Five different frequencies were normalized with the base line frequency (0.125 Hz n=15) in this analysis: 0.05 Hz (n=6), 0.166 Hz (n=6), 0.2 Hz (n=10), 0.25 Hz (n=10), and 0.4 Hz (n=8).
  
  
  RESULTS
  The lowest frequency (0.05 Hz) revealed significant differences (p<.05) for all parameters (torque, passive angular velocity, axial velocity [AV], axial reaction force [RF], and energy loss [EL]) with respect to all other frequencies. Significant differences (p<.05) were observed in the following: torque (0.4 Hz with respect to 0.2 Hz and 0.25 Hz), passive sagittal angular velocity (SAV) (0.4 Hz with respect to all other frequencies; 0.166 Hz with respect to 0.25 Hz), axial linear velocity (0.4 Hz with respect to all other frequencies), and RF (0.4 Hz with respect to 0.2 Hz and 0.25 Hz). Strong correlations (R2>0.75, p<.05) were observed between RF with intradiscal pressure (IDP) and AR angular displacement with IDP. Intradiscal pressure (p<.05) was significantly larger in 0.2 Hz in comparison with 0.125 Hz.
  
  
  CONCLUSIONS
  Evidences suggest that measurements at very small frequencies (0.05 Hz) of torque, SAV, AV, RF, and EL are significantly reduced when compared with higher frequencies (0.166 Hz, 0.2 Hz, 0.25 Hz, and 0.4 Hz). Higher frequencies increase torque, RF, passive SAV, and AV. Higher frequencies induce a greater IDP in comparison with lower frequencies.
authors.affiliation: NeuroOncology Program, H. Lee Moffitt Cancer Center & Research Institute, 13131 Magnolia Drive, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33620, USA; Department of Mechanical Engineering, University of South Florida, 4202 E Fowler Ave, Tampa, FL 33620, USA. Electronic address: james.doulgeris@moffitt.org.
authors.forename: James J
authors.initials: JJ
authors.lastname: Doulgeris
authors.affiliation: NeuroOncology Program, H. Lee Moffitt Cancer Center & Research Institute, 13131 Magnolia Drive, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33620, USA.
authors.forename: Sabrina A
authors.initials: SA
authors.lastname: Gonzalez-Blohm
authors.affiliation: NeuroOncology Program, H. Lee Moffitt Cancer Center & Research Institute, 13131 Magnolia Drive, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33620, USA.
authors.forename: Kamran
authors.initials: K
authors.lastname: Aghayev
authors.affiliation: NeuroOncology Program, H. Lee Moffitt Cancer Center & Research Institute, 13131 Magnolia Drive, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33620, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Shea
authors.affiliation: Department of Chemical & Biomedical Engineering, University of South Florida, 4202 E Fowler Ave, Tampa, FL 33620, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, University of South Florida, 4202 E Fowler Ave, Tampa, FL 33620, USA.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Hess
authors.affiliation: NeuroOncology Program, H. Lee Moffitt Cancer Center & Research Institute, 13131 Magnolia Drive, Tampa, FL 33612, USA; Department of Neurosurgery and Orthopedics, College of Medicine, University of South Florida, 12901 Bruce B Downs Blvd, Tampa, FL 33620, USA.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Vrionis
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011312:Pressure; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D016474:Weight-Bearing
keywords: Axial displacement; Energy loss; Intradiscal pressure; Loading rate; Passive motion; Range of motion