Sciatica can happen because of any condition that affects the sciatic nerve. It can also happen because of conditions affecting any of the five spinal nerves that bundle to form the sciatic nerve. Conditions that can cause sciatica include: Herniated disks. Degenerative disk disease. Spinal stenosis. Foraminal stenosis. Spondylolisthesis. Osteoarthritis. Injuries. Pregnancy. Tumors, cysts or other growths. Conus medullas syndrome. Cauda equina syndrome.