Herniated disc or herniated nucleus pulposus (HNP) occurs with age or injury, the center of vertebral discs may start to lose water content, making the disc less effective as a cushion, causing displacement of the disc's center (herniated or ruptured disc) through a crack in the outer layer. Most disc herniations occur in the bottom two discs of the lumbar spine, at and just below the waist. A herniated disc can press on a nerve root in the spine and may cause back pain or pain, numbness, tingling or weakness of the leg called sciatica or radiculopathy. Also known as a slipped or ruptured disc, or herniated nucleus pulposus (HNP). Can also occur in the neck and lumbar but rarely in the thoracic portion of the spine.