Sciatica can be caused by anything that irritates the nerves in the lower lumbar spine that come together to form the sciatic nerve. The most common cause of sciatica is a disc herniation in the lower lumbar spine that pinches one of the nerves as it’s traveling out of the spine into the leg. The other causes can be spinal stenosis, which is a term that refers to a tightening around the space where the nerves are. It can also be caused by scar tissue, usually that forms after surgery in the lumbar spine that compresses and irritates the nerves in the lower lumbar spine. Other cause of sciatica can include degenerative disc disease or a lumbar spondylolisthesis, which refers to a slippage of one of the vertebra in the lumbar spine on another that causes a tightening in the exit zone of the nerves that pinches the nerve as they are exiting. Other causes can be fractures, tumors, or other rare conditions that put pressure on the nerves and irritate the nerves, causing pain and numbness and tingling that goes down the leg.