Abstract
BackgroundLaboratory 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.MethodsThree 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.ResultsRange 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).ConclusionsBased 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.
Highlights
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
The current study examined the anatomy and biomechanical aspects of this synthetic biomimetic spine model in cyclic testing; and to evaluate anterior and lateral plating with interbody cages, to address the following questions: 1) is a lateral interbody cage + plate construct mechanically comparable to an anterior interbody cage + plate construct; and 2) is a stand-alone lateral interbody cage construct mechanically comparable to the intact state
For neutral zone (NZ) results, most FE NZ and lateral bending (LB) NZ were in the range of the cadaveric data, but the axial rotation (AR) NZ was smaller than reported human results
Summary
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. The goal of current study is to evaluate the properties of a synthetic biomimetic spine model; to assess the mechanical performance of lateral plating following lateral interbody fusion. Animals are a suitable replacement for human cadaveric spines in certain testing protocols [4-11] with well reported anatomical and biomechanical comparisons [12,13] but have limitation in terms of size and angle of lordosis. While these samples may be more accessible and more cost effective, they still embody the previously mentioned limitations with human tissues
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