Direction-dependent constriction flow in a poroelastic solid: The intervertebral disc valve

We hypothesize that a direction-dependent flow resistance exists in the int ervertebral disc due to constriction flow in the cartilage endplates. A com parison of the hydrostatic pressure in the nucleus of the healthy intervert ebral disc during daily loading with the relatively low osmotic swelling pr essure during rest, suggests the necessity of such direction-dependent flow resistance to ensure that all the fluid exuded from the disc during loadin g is recovered during rest. A physical model demonstrating the direction-de pendent resistance of constriction flow in a poroelastic solid is presented . A finite element model was developed and validated against this physical model. The finite element model showed that decrease of the constriction ho le area not only increases the resistance to fluid flow, hut also causes th e direction-dependency of flow resistance to decrease. Through this mechani sm, endplate sclerosis could affect normal daily fluid exchange in the inte rvertebral disc, resulting in decreased mass transport and/or dehydration o f the disc. [S0148-0731(00)00406-4].