title: Biomechanical evaluation of a biomimetic spinal construct.
abstract: BACKGROUND
  Laboratory spinal biomechanical tests using human cadaveric or animal spines have limitations in terms of disease transmission, high sample variability, decay and fatigue during extended testing protocols. Therefore, a synthetic biomimetic spine model may be an acceptable substitute. The goal of current study is to evaluate the properties of a synthetic biomimetic spine model; also to assess the mechanical performance of lateral plating following lateral interbody fusion.
  
  
  METHODS
  Three L3/4 synthetic spinal motion segments were examined using a validated pure moment testing system. Moments (±7.5 Nm) were applied in flexion-extension (FE), lateral bending (LB) and axial rotation (AR) at 1Hz for total 10000 cycles in MTS Bionix. An additional test was performed 12 hours after 10000 cycles. A ±10 Nm cycle was also performed to allow provide comparison to the literature. For implantation evaluation, each model was tested in the 4 following conditions: 1) intact, 2) lateral cage alone, 3) lateral cage and plate 4) anterior cage and plate. Results were analysed using ANOVA with post-hoc Tukey's HSD test.
  
  
  RESULTS
  Range of motion (ROM) exhibited logarithmic growth with cycle number (increases of 16%, 37.5% and 24.3% in AR, FE and LB respectively). No signification difference (p > 0.1) was detected between 4 cycles, 10000 cycles and 12 hour rest stages. All measured parameters were comparable to that of reported cadaveric values. The ROM for a lateral cage and plate construct was not significantly different to the anterior lumbar interbody construct for FE (p = 1.00), LB (p = 0.995) and AR (p = 0.837).
  
  
  CONCLUSIONS
  Based on anatomical and biomechanical similarities, the synthetic spine tested here provides a reasonable model to represent the human lumbar spine. Repeated testing did not dramatically alter biomechanics which may allow non-destructive testing between many different procedures and devices without the worry of carry over effects. Small intra-specimen variability and lack of biohazard makes this an attractive alternative for in vitro spine biomechanical testing. It also proved an acceptable surrogate for biomechanical testing, confirming that a lateral lumbar interbody cage and plate construct reduces ROM to a similar degree as anterior lumbar interbody cage and plate constructs.
authors.affiliation: Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, University of New South Wales, Clinical Science Bldg, Prince of Wales Hospital, Gate 6, Avoca Street, Sydney, 2031, Australia. wt0706@gmail.com.|Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia. wt0706@gmail.com.
authors.forename: Tian
authors.initials: T
authors.lastname: Wang
authors.affiliation: Royal North Shore Hospital, St Leonards, NSW, Australia. drball@neurospine.com.au.
authors.forename: Jonathon R
authors.initials: JR
authors.lastname: Ball
authors.affiliation: Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, University of New South Wales, Clinical Science Bldg, Prince of Wales Hospital, Gate 6, Avoca Street, Sydney, 2031, Australia. m.pelletier@unsw.edu.au.
authors.forename: Mattew H
authors.initials: MH
authors.lastname: Pelletier
authors.affiliation: Surgical & Orthopaedic Research Laboratories, Prince of Wales Clinical School, University of New South Wales, Clinical Science Bldg, Prince of Wales Hospital, Gate 6, Avoca Street, Sydney, 2031, Australia. wrwalshau@gmail.com.
authors.forename: William R
authors.initials: WR
authors.lastname: Walsh
keywords: Anterior plate; Biomechanical; Fatigue; Interbody cage; Lateral plate; Lumbar; Motion segment; Pure moment; Sawbones; Sowbones; Synthetic