title: Biomechanical comparison of anterior versus posterior lumbar threaded interbody fusion cages.
abstract: METHODS
  Biomechanical flexibility tests were performed in specimens receiving anterior lumbar interbody fixation or posterior lumbar interbody fixation using dual threaded cages.
  
  
  OBJECTIVE
  To determine differences in stability between anterior lumbar interbody fixation and posterior lumbar interbody fixation immediately after surgery and after fatigue.
  
  
  BACKGROUND
  No direct biomechanical comparison of lumbar fixation with threaded anterior lumbar interbody fixation or posterior lumbar interbody fixation cages has been performed previously. METHODS.: Sixteen anterior lumbar interbody fixation specimens and 16 posterior lumbar interbody fixation specimens underwent nondestructive biomechanical testing. Flexibility was assessed during applied flexion, extension, lateral bending, axial rotation, and anteroposterior shear before and after fixation and fatigue. After testing, specimens were dissected, and the quality of fixation was graded.
  
  
  RESULTS
  Variability in angular range of motion after fixation was greater than normal interspecimen variability by 89% after anterior lumbar interbody fixation and by 117% after posterior lumbar interbody fixation. During flexion-extension and lateral bending, posterior lumbar interbody fixation allowed a mean of 60% smaller neutral zones than anterior lumbar interbody fixation (P < 0.05, nonpaired Student t test). During axial rotation, anterior lumbar interbody fixation allowed 15% less range of motion than posterior lumbar interbody fixation unless facets were kept intact with posterior lumbar interbody fixation (6 of 16 specimens), in which case anterior lumbar interbody fixation allowed 41% greater range of motion than posterior lumbar interbody fixation. During anteroposterior shear, both anterior lumbar interbody fixation and posterior lumbar interbody fixation restrained range of motion to within 50% of normal. Anterior lumbar interbody fixation loosened, on average, 130% more with fatigue than posterior lumbar interbody fixation during anteroposterior shear.
  
  
  CONCLUSIONS
  Both anterior lumbar interbody fixation and posterior lumbar interbody fixation provided inconsistent stability. Therefore, stand-alone anterior lumbar interbody fixation or posterior lumbar interbody fixation may often be ineffective clinically. During all modes of loading except axial rotation, posterior lumbar interbody fixation performed slightly better than anterior lumbar interbody fixation, perhaps due to deeper hole preparation and destruction of anterior stabilizers necessary for anterior lumbar interbody fixation. Avoiding resection of facets during posterior lumbar interbody fixation led to significantly better performance during axial rotation.
authors.affiliation: Spinal Biomechanics Research Laboratory, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona, USA.
authors.forename: A Giancarlo
authors.initials: AG
authors.lastname: Vishteh
authors.forename: Neil R
authors.initials: NR
authors.lastname: Crawford
authors.forename: Robert H
authors.initials: RH
authors.lastname: Chamberlain
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Thramann
authors.forename: Sung Chan
authors.initials: SC
authors.lastname: Park
authors.forename: J Bradley
authors.initials: JB
authors.lastname: Craigo
authors.forename: Volker K H
authors.initials: VK
authors.lastname: Sonntag
authors.forename: Curtis A
authors.initials: CA
authors.lastname: Dickman
mesh_terms: D001696:Biomechanical Phenomena / Q000379:methods*; D002102:Cadaver; D005260:Female; D006801:Humans; D016268:Internal Fixators; D007593:Joint Instability; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D019736:Prostheses and Implants; D016059:Range of Motion, Articular; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D021801:Zygapophyseal Joint