The sciatic nerve (nervus ischiadicus) leaves the spinal cord at the level of the lower lumbar vertebrae and the sacrum and pulls towards the leg. It runs over the buttocks to the back of the thigh and branches into two branches above the hollow of the knee, which extend from the rear and lateral lower legs to the sole of the foot and the outer edge of the foot. The term sciatica is commonly used to describe a pain that follows the course of the nerve tract. It is caused by irritation of the sciatic nerve when the nerve roots emerge from the spinal canal. Causes are often herniated discs or wear of the intervertebral joints. If typical sciatic pain is associated with low back pain, it is called lumboischialgia.