THE STUDY OF RADIAL TEARS IN INTERVERTEBRAL DISC BY THE POROELASTIC SIMULATION: METHODOLOGY AND THE COMPRESSIVE CASE

摘要

The intervertebral disc (IVD) is a three-dimensional, biphasic structure containing fluid and solid skeleton; fluid may flow through pores of solid tissues and bones that plays an important pumping role in the support of the solid skeleton and for further nutrition transportation in the IVD. Swelling pressure (SP) is mainly caused by the fluid motion and the straining of the solid skeleton in the biphasic structure that affects stress levels generated in the medium and may possibly cause the tissue rupture. In aging or herniated IVDs, radial tears on the tissue structure is always found; however, relevance between such tears and the mechanical stresses is still uncertain. Experimental inspection for the previous problems is still unable to reach. Therefore, the poroelastic finite element study on such subject is encouraged for the understanding of pathological problems occurred in the spine. To revise the related formulations, an intensive process beginning with the biphasic equilibrium is introduced that derives solid–fluid interactive equations on the SP and various stresses under exclusive domains. A contingent poroelastic finite element model of the IVD is also introduced. The SP in the annular fibrosis closed to the periphery of radial tears is disturbed that makes further variation of geometry and stress levels in the IVD; the load-bearing function of the structure is thus changed. The simulating procedures proposed in the study are significant for further studies on the IVD and biological tissues and bones.