Does Annulus Fibrosus Lamellar Adhesion Testing Require Preconditioning?

The interlamellar matrix (ILM), located between the annular layers of the intervertebral disc (IVD), is an adhesive component which acts to resist delamination. Investigating the mechanical properties of the ILM can provide us with valuable information regarding risk of disc injury; however given its viscoelastic nature, it may be necessary to conduct preconditioning on tissue samples before measuring these ILM properties. Therefore, the aim of this study was to optimize mechanical testing protocols of the ILM by examining the effect of preconditioning on stiffness and strength of this adhesive matrix. Eighty-eight annular samples were dissected from 22 porcine cervical discs and randomized into one of four testing conditions consisting of ten cycles of 15% strain followed by a 180 deg adhesive peel test. The four testing groups employed a different strain rate for the ten cycles of preconditioning: 0.01 mm/s (n = 23); 0.1 mm/s (n = 26); 1 mm/s (n = 23); and no preconditioning employed (n = 16). Samples preconditioned at 0.01 mm/s were significantly less stiff than those that had not received preconditioning (p = 0.014). No other results were found to be statistically significant. Given the lack of differences observed in this study, preconditioning is likely not necessary prior to conducting a 180 deg peel test. However, if preconditioning is employed, the findings from this study suggest avoiding preconditioning conducted at very slow rates (i.e., 0.01 mm/s) as the long testing time may negatively affect the tissue.