A herniated disc (also called bulged, slipped or ruptured) is a fragment of the disc nucleus that is pushed out of the annulus, into the spinal canal through a tear or rupture in the annulus. Discs that become herniated usually are in an early stage of degeneration. The spinal canal has limited space, which is inadequate for the spinal nerve and the displaced herniated disc fragment. Due to this displacement, the disc presses on spinal nerves, often producing pain, which may be severe. Herniated discs can occur in any part of the spine. Herniated discs are more common in the lower back (lumbar spine), but also occur in the neck (cervical spine). The area in which pain is experienced depends on what part of the spine is affected.
A single excessive strain or injury may cause a herniated disc. However, disc material degenerates naturally as one ages, and the ligaments that hold it in place begin to weaken. As this degeneration progresses, a relatively minor strain or twisting movement can cause a disc to rupture. Certain individuals may be more vulnerable to disc problems and, as a result, may suffer herniated discs in several places along the spine. Research has shown that a predisposition for herniated discs may exist in families with several members affected.