False-colour three-dimensional computed tomography (CT) scan of a slipped (prolapsed) disc between lumbar vertebrae. Bone is coloured yellow. The intervertebral disc, a flexible plate of cartilage which cushions adjacent vertebrae (spine bones), is blue. Here it has prolapsed into the vertebral canal (centre) which contains the spinal cord. The lower back lumbar vertebrae are most affected by this condition, caused by back strain, mechanical injury or sudden pressure. Backache, numbness and paralysis can occur, or sciatica (leg pain) if adjoining nerve roots are pinched. Treatment may include bed rest, traction or surgery.