Feasibility Analysis of Viscosupplement and Crosslinker in Recovering the Biomechanical Functions of Degenerated Intervertebral Disc
Date Issued
2010
Date
2010
Author(s)
Kuo, Ya-Wen
Abstract
The major biomechanical functions of intervertebral disc are to resist the external load and to dissipate the shock energy imposed on the human body during daily activities. The disc functions depend on the internal fluid dynamics and compositional integrity of disc matrix. The clarifications of effect of loading conditions and degenerations on the biomechanical functions of disc will improve the treatment efficacy for the degenerated disc diseases. Two biomechanical models, i.e., rheological model and the dynamic model, have been used to simulate the disc medium term and short term behaviors. The rheological model is traditionally described by a linear biphasic theory model, and the dynamic model is described by a 1-D spring and dashpot model. The rheological and dynamic properties derived from the both models can indicate the disc stiffness and internal fluid flow capability of disc matrix and different time scale.
The first part of this dissertation studied the effect of loading history, loading magnitude, fatigue loading and degeneration on the disc rheology. The results showed that the disc stiffness increased and the fluid flow capability decreased during the creep loading, the disc stiffness decreased and the fluid flow capability unchanged during the relaxation loading. The disc stiffness increased and the fluid flow capability decreased with the loading magnitude. After the fatigue loading time, the disc stiffness unchanged but the fluid flow capability decreased. The degeneration increased the disc stiffness but decreased the fluid flow capability. The results suggested that the disc stiffness was negatively related to the disc hydration level, and the fluid flow capability was positively related to the matrix pore size.
In the second part of this study, the recovery efficiency of viscosupplement (i.e., hyaluronic acid) and crosslinker (i.e., genipin) on the degenerated disc was evaluated by changes of the water content and viscoelasticity of nucleus pulposus, structural integrity of the anular fibrosus, and dynamic properties of the whole disc responding to the fatigue loading. The results revealed that the intervention of hyaluronic acid and genipin could recover the water content of the degenerated nucleus pulposus after rest, but block the water outflow during the fatigue loading. The genipin could slightly increase the elasticity of the degenerated nucleus pulposus and condense the delaminated anular fibrosus. Neither the intervention of hyaluronic acid nor the genipin recovered the viscoelasticity of the degenerated nucleus pulposus. The intervention of hyaluronic acid and genipin could recover the disc stiffness and energy dissipation capability of the degenerated disc. However, these effects are degraded by the fatigue loading. The results indicated that the crosslinker could better recover the structural and mechanical properties of the degenerated disc than the viscosupplement does. However, the susceptibility to the fatigue loading casts the doubt on the feasibility of crosslinker to treat the degenerated disc diseases.
In conclusion, this dissertation proves that the disc mechanical functions are affected by the loading conditions and degeneration due to the change of disc hydration level and matrix pore size. The disc stiffness increased and the internal fluid flow capability decreased with degeneration. Neither the viscosupplement nor the crosslinker is feasible to reverse the full aspects of disc degenerative changes. New materials for treating degenerated disc should be studied in the future.
Subjects
Degenerated disc diseases
Spine biomechanics
Disc rheology
Stiffness
Damping coefficient
Genipin
Hyaluronic acid
SDGs
Type
thesis
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