title: Enhancing the stability of anterior lumbar interbody fusion: a biomechanical comparison of anterior plate versus posterior transpedicular instrumentation.
abstract: METHODS
  Biomechanical study using human cadaver spines.
  
  
  OBJECTIVE
  To assess the stabilizing effect of a supplemental anterior tension band (ATB, Synthes) plate on L5-S1 anterior lumbar interbody fusion (ALIF) using a femoral ring allograft (FRA) under physiologic compressive preloads, and to compare the results with the stability achieved using FRA with supplemental transpedicular instrumentation.
  
  
  BACKGROUND
  Posterior instrumentation can improve the stability of ALIF cages. Anterior plates have been proposed as an alternative to avoid the additional posterior approach.
  
  
  METHODS
  Eight human specimens (L3 to sacrum) were tested in the following sequence: (i) intact, (ii) after anterior insertion of an FRA at L5-S1, (iii) after instrumentation with the ATB plate, and (iv) after removal of the plate and adding transpedicular instrumentation at the same level. Specimens were tested in flexion-extension, lateral bending, and axial rotation. Flexion-extension was tested under 0 N, 400 N, and 800 N compressive follower preload to simulate physiologic compressive preloads on the lumbar spine.
  
  
  RESULTS
  Stand-alone FRAs significantly decreased the range of motion (ROM) in all tested directions (P < 0.05); however, the resultant ROM was large in flexion-extension ranging between 6.1 +/- 3.1 degrees and 5.1 +/- 2.2 degrees under 0 N to 800 N preloads. The ATB plate resulted in a significant additional decrease in flexion-extension ROM under 400 N and 800 N preloads (P < 0.05). The flexion-extension ROM with the ATB plate was 4.1 +/- 2.3 under 0 N preload and ranged from 3.1 +/- 1.8 to 2.4 +/- 1.3 under 400 N to 800 N preloads. The plate did not significantly decrease lateral bending or axial rotation ROM compared with stand-alone FRA (P > 0.05), but the resultant ROM was 2.7 +/-1.9 degrees and 0.9 +/- 0.6 degrees , respectively. Compared with the ATB plate, the transpedicular instrumentation resulted in significantly less ROM in flexion-extension and lateral bending (P < 0.05), but not in axial rotation (P > 0.05).
  
  
  CONCLUSIONS
  The ATB plate can significantly increase the stability of the anterior FRA at L5-S1 level. Although supplemental transpedicular instrumentation results in a more stable biomechanical environment, the resultant ROM with the addition of a plate is small, especially under physiologic preload, suggesting that the plate can sufficiently resist motion. Therefore, clinical assessment of the ATB plate as an alternative to transpedicular instrumentation to enhance ALIF cage stability is considered reasonable.
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, Maywood, IL 60153, USA.
authors.forename: Michael N
authors.initials: MN
authors.lastname: Tzermiadianos
authors.forename: Anis
authors.initials: A
authors.lastname: Mekhail
authors.forename: Leonard I
authors.initials: LI
authors.lastname: Voronov
authors.forename: Jason
authors.initials: J
authors.lastname: Zook
authors.forename: Robert M
authors.initials: RM
authors.lastname: Havey
authors.forename: Susan M
authors.initials: SM
authors.lastname: Renner
authors.forename: Gerard
authors.initials: G
authors.lastname: Carandang
authors.forename: Celeste
authors.initials: C
authors.lastname: Abjornson
authors.forename: Avinash G
authors.initials: AG
authors.lastname: Patwardhan
mesh_terms: D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D019245:Compressive Strength; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology / Q000601:surgery*; D016059:Range of Motion, Articular / Q000502:physiology; D012447:Sacrum / Q000502:physiology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical; D016474:Weight-Bearing