Q.An elderly woman slipped in the bathroom and had severe pain in her lower back. After X-ray examination doctors told her it is due to a slipped disc. What does that mean? How does it affect our health?

A "slipped disc" (a herniated or prolapsed intervertebral disc) means that the pad of fibrocartilage cushioning two adjacent vertebrae has ruptured or bulged out of its normal position between them. Vertebrae are joined by cartilaginous joints, which allow only limited movement, and the intervertebral disc is exactly this cushioning cartilage; when it slips, its soft inner material can press against the spinal cord running through the vertebrae's neural canal, or against a nerve root branching off it. That pressure on nervous tissue is what produces severe, often sharp lower-back pain, and can also cause numbness, tingling, or weakness …

The vertebral column is a chain of vertebrae running along the back, each connected to its neighbours by a cartilaginous joint -- a joint type that allows only limited movement because a pad of cartilage, the intervertebral disc, sits between the bony surfaces. Each vertebra also has a central hollow, the neural canal, through which the spinal cord passes, with individual spinal nerves branching off at each vertebral level.

A slipped disc happens when this intervertebral disc's tougher outer ring weakens or tears, letting its softer inner core bulge or rupture outward, out of its normal position between the two vertebrae. Because the vertebral column sits so close to the spinal cord and its branching nerves, a disc displaced this way can press directly against the spinal cord itself or against a nearby spinal nerve root. …