A novel in-vitro model of intervertebral disc degeneration using hyperphysiological loading.

Intervertebral disc (IVD) degeneration includes changes in tissue biomechanics, physical attributes, biochemical composition, disc microstructure, and cellularity, which can all affect the normal function of the IVD, and ultimately may lead to pain. The purpose of this research was to develop an in-vitro model of degeneration that includes the evaluation of physical, biomechanical, and structural parameters, and that does so over several load/recovery periods. Hyperphysiological loading was used as the degenerative initiator with three experimental groups employed using bovine coccygeal IVD specimens: Control; Single-Overload; and Double-Overload. An equilibrium stage comprising a static load followed by two load/recovery periods was followed by six further load/recovery periods. In the Control group all load/recovery periods were the same, comprising physiological cyclic loading. The overload groups differed in that hyperphysiological loading was applied during the 4th loading period (Single-Overload), or the 4th and 5th loading period (Double-Overload). Overloading led to a significant reduction in disc height compared to the Control group, which was not recovered in subsequent physiological load/recovery periods. However, there were no significant changes in stiffness. Overloading also led to significantly more microstructural damage compared to the Control group. Taking all outcome measures into account, the overload groups were evaluated as replicating clinically relevant aspects of moderate IVD degeneration. Further research into a potential dose-effect, and how more severe degeneration can be replicated would provide a model with the potential to evaluate new treatments and interventions for different stages of IVD degeneration.