A condition in which an intervertebral disc becomes displaced or where the soft centre of a disc passes through the hard cartilage of the exterior and presses onto a nerve.
The spinal column is built up of a series of bones, known as vertebrae, placed one upon the other. Between these vertebrae lies a series of thick discs of fibro-cartilage known as intervertebral discs. Each disc consists of an outer portion known as the annulus fibrosus, and an inner core known as the nucleus pulposus. The function of these discs is to give flexibility and resiliency to the spinal column and to act as buffers against undue jarring. In other words, they are most efficient shock-absorbers. They may, however, prolapse, or protrude, between the two adjacent vertebrae. If this should happen they press on the neighbouring spinal nerve and cause pain. As the most common sites of protrusion are between the last two lumbar vertebrae and between the last lumbar vertebra and the sacrum, this means that the pain occurs in the back, causing lumbago, or down the course of the sciatic nerve causing sciatica. The prolapse is most likely to occur in middle age, which suggests that it may be associated with degeneration of the disc involved, but it can occur in early adult life as well. It usually occurs when the individual is performing some form of exercise which involves bending or twisting, as in gardening. The onset of pain may be acute and sudden, or gradual and more chronic in intensity.