title: Evaluation of spinal kinematics following lumbar total disc replacement and circumferential fusion using in vivo fluoroscopy.
abstract: METHODS
  In vivo fluoroscopic analysis of lumbar spinal motion with total disc replacement (TDR), fusions, and controls.
  
  
  OBJECTIVE
  Compare and contrast lumbar spinal motion profiles in TDR, circumferential fusion, and controls.
  
  
  BACKGROUND
  TDR has been shown to preserve motion and possibly prevent abnormal loading at the adjacent level. Although in vitro cadaveric studies have provided invaluable information, they are not capable of assessing the physiologic motion profile of the lumbar spine that is initiated and stabilized by in vivo trunk muscular contractions.
  
  
  METHODS
  Cross-sectional evaluation using high-frequency low-dose pulsated video fluoroscopy to evaluate lumbar spinal motion in subjects who underwent TDR (n = 8), circumferential fusion (n = 5), and controls (n = 4). Angulation and translation were recorded at 20 time points during the extension-flexion arc. Motion gradients, or slopes of the motion curves, were generated to allow for comparison of lumbar spinal motion profiles.
  
  
  RESULTS
  Circumferential fusions exhibited significantly steeper motion gradients at the proximal adjacent level compared with TDR during flexion. TDR had more physiologic motion profiles at the proximal adjacent level than fusions during flexion and extension. At operative levels L4/5 and L5/S1, TDR and controls exhibited similar motion profiles in flexion, while fusions exhibited significantly less motion. In extension, however, TDR had a steeper slope than controls at the L4/5 operative level. Between L3 and S1, the total range of motion accounted for by the L4/5 proximal adjacent level was 59% in 1-level fusions, 38% in 1-level TDR, and 29% in controls. While no control or TDR subjects underwent sagittal plane translation >3 mm during flexion-extension, 80% of fusions did (average 3.7 mm), most notably during the latter phase of extension.
  
  
  CONCLUSIONS
  TDR produces physiologic lumbar spinal motion profiles in flexion and extension at the operative and proximal adjacent levels. Fusions, however, produced steeper motion gradients at the proximal adjacent level, while undergoing significantly greater sagittal plane translation during flexion-extension.
authors.affiliation: Department of Orthopaedic Surgery, The University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Auerbach
authors.forename: Brian P D
authors.initials: BP
authors.lastname: Wills
authors.forename: Theresa C
authors.initials: TC
authors.lastname: McIntosh
authors.forename: Richard A
authors.initials: RA
authors.lastname: Balderston
mesh_terms: D000328:Adult; D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005260:Female; D005471:Fluoroscopy / Q000379:methods; D005500:Follow-Up Studies; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012399:Rotation; D013123:Spinal Fusion; D013997:Time Factors; D016896:Treatment Outcome; D014741:Video Recording