As a disc degenerates or become traumatized, the soft inner gel in the disc can leak back into the spinal canal. This is known as disc herniation. Once inside the spinal canal, the herniated disc material can put pressure on the nerve, causing pain to radiate down the nerve leading to sciatica or leg pain (from a lumbar herniated disc) or arm pain (from a cervical herniated disc). Disc herniations can also cause back pain as the stabilizing disc material left behind has lost its integrity.