Inter-vertebral discs are thick, fibrous cartilaginous discs that connect and lie between adjacent vertebrae of the backbone. They permit rotational and bending movement of the back and make up approximately 25 percent of the length of the backbone, acting as shock absorbers and providing cushioning for the brain and spinal cord. Each disc has an outer fibrous layer over a pulpy centre. A slipped or prolapsed disc is caused by the inner layer being pushed through the fibrous layer to impinge upon a neighbouring spinal nerve, causing pain.

The main symptom is pain in the lower part of the back which may come on and worsen gradually. More commonly it is sudden and occurs during an activity that involves bending or sudden twisting of the backbone. The cause is related to degenerative changes and weak muscles. Bed rest on a flat, firm surface, possibly with physiotherapy at a later stage helps recovery.