Simulation of the Progression of Intervertebral Disc Degeneration Due to Decreased Nutritional Supply

Study Design. Simulate the progression of human disc degeneration. Objective. The objective of this study was to quantitatively analyze and simulate the changes in cell density, nutritional level, proteoglycan (PG) content, water content, and volume during human disc degeneration using a numerical method. Summary of Background Data. Understanding the cause and progression of intervertebral disc degeneration is crucial for developing effective treatment strategies for intervertebral disc degeneration-related diseases. During tissue degeneration, the disc undergoes losses of cell viability and activities, changes in extracellular matrix composition and structure, and compromise of the tissue-level integrity and function, which is significantly influenced by the intercoupled biological, chemical, electrical, and mechanical signals in the disc. Characterizing these signals in human discs in vivo is difficult. Methods. A realistic 3-dimensional finite element model of the human intervertebral disc was developed on the basis of biomechanoelectrochemical continuum mixture theory. The theoretical framework and the constitutive relationships were all biophysics based. All the material properties were obtained from experimental results. The cell-mediated disc degeneration process caused by lowered nutritional levels at disc boundaries was simulated and validated by comparing with experimental results. Results. Cell density reached equilibrium state in 30 days after reduced nutritional supply at the disc boundary, whereas the PG and water contents reached a new equilibrium state in 55 years. The simulated results for the distributions of PG and water contents within the disc were consistent with the results measured in the literature, except for the distribution of PG content in the sagittal direction. Conclusion. Poor nutritional supply has a long-term effect on disc degeneration.