Pulposus Essay

Due to the intervertebral disc specific structure and the interactions between nucleus pulposus and annulus fibrosus, it is capable to resist high compressive loads and provide spinal mobility (Tang, Liu, & Zhang, 2014). The nucleus pulpous is capable to endure high compressive forces because of its high water content, low permeability and osmotic properties (Galbusera et al., 2014). It works by distributing hydraulic pressure in multiple directions within each intervertebral disc under compressive loads, which is a result of the nucleus pulposus being centered by the endplates and the annulus fibrosus. The aggrecan synthesized by the nucleus pulposus cells is highly negatively charged that enables the nucleus pulposus to swell by absorbing water. However, there are positive cations in the interstitial fluid, thus that charges are electrically balanced. In order to the higher concentration of cations, the disc undergoes an osmotic pressure (Donnan equilibrium). Subsequently, that gives the capacity to attract and absorb water, with the respect to the hydrostatic pressure (Urban & McMullin, 1988). Both under active loading and at rest, the pressure in the nucleus pulposus is balanced by tensile stresses in the annulus fibrosus, which restrain swelling and prevent collapse of the disc under compression (Tang, Liu, & Zhang, 2014). To cope with the other types of loading from daily activities, such as bending and move in multiple directions, the unique annular lamellar structure of
rotating collagen fibers is loaded primarily in tension, which is similar to the fiber strengthening of a tire, when combined with an almost isovolumetric NP core (Galbusera et al., 2014).
Finally, the endplates participate in the distribution of the pressure that playing a role within the nucleus pulposus and tension in the annulus fibrosus of the vertebral bodies (Adams et al, 1996).The viscous fluid moves through the endplates, and the visco elastic stretching feature of collagen fibers in the annulus enables the disc to withstand loads.
Due to this fluid exchange, the intervertebral disc exhibits the creep and relaxation behavior under sustained loads typical of a
damper.
Once the spine is under pressure, the jelly-like annulus fibrosus redistributes itself to imbibe the impact of the pressure. The gel becomes dehydrated with aging and the spine is able to absorb less shock. Moreover, the outer layer in the annulus fibrosus degenerates with aging and can begin to tear, and this lead to chronic back pain for some people.