Intervertebral Discs and Back Pain

pulpy, formed by a gelatinous substance consisting of over 88% water;

an external annular part, the fibrous ring, characterized by fibro-cartilaginous structures arranged in concentric layers around the central core.

The anterior part directed towards the abdomen is usually thicker and stronger than the corresponding posterior part

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The function of the nucleus pulposus is to redistribute the compressive forces in the various segments of the spine, allowing the vertebrae significant micro-movements in every direction, which when added together translate into those movements of great amplitude that characterize our spine.

The fibrous ring, on the other hand, has the function of keeping the vertebral bodies in close contact, of containing the nucleus pulposus and of resisting tension.

, the nourishment of the latter takes place by osmosis processes, diffusion and, above all, thanks to a pump mechanism for which a decrease in pressure facilitates the entry of nutritional substances and slows down the expulsion of catabolites, while its increase determines the inverse condition (Caillet, 1973; Kapandji, 1974; Kroemer, 1985). To ensure the health of the disc, the optimum of the nutritional process is determined by the constant alternation of loading and unloading conditions around a threshold value that is would be around 80 kg of lumbar intradiscal pressure (the threshold value is the discriminating element between overload conditions and underload conditions). On the other hand, prolonged overload and underload conditions, such as those that can occur in prolonged fixed postures, hinder nutritional turnover and can in the long term favor disc degeneration processes (Grieco, 1986, Kapandji, 1974)

When pressure is applied to the disc (e.g. flexion movement of the spine), the nourishing fluids flow out and the thickness of the disc itself is reduced

By reverse mechanism, if pressure is removed (eg during sleep) there is a recall of liquids towards the inside of the disc and a restoration of its structure.

The deformation of the disc is essentially linked to the deformation of its solid matrix if the time of application of the load is less than two seconds, to the leakage of water if the time of application of the load is greater than two seconds (Turek, 1977).

In the first case, the change in shape of the disc is not accompanied by a change in volume, and when the load is removed the recovery of the original shape is immediate, or almost (elastic behavior); in the second case there is always a reduction in the volume of the disk, proportional to the quantity of water squeezed out, and the recovery of the original shape after the removal of the load always requires a certain time.

Studies by Adams et al. have shown that the disc, kept under a compressive load of 1000 Newton for two hours, is reduced in height by about mm 2.