The sciatic nerve is the largest and longest nerve in the body. It begins in the lower back, where it branches off from the spinal cord, and runs through the buttocks and down the back of each leg. Lumbar radiculopathy, also called sciatica, occurs when the sciatic nerve in the lower back is compressed, irritated, or inflamed. This can cause pain in the lower back, buttocks or legs along with numbness, tingling or a burning sensation down the legs, and weakness in the legs and feet. The most common cause of lumbar radiculopathy is a herniated disc in the lumbar spine, which can put pressure on the nerve roots as they exit the spinal cord. Other causes may include spinal stenosis (narrowing of the spinal canal), degenerative disc disease and osteoarthritis of the spine.