Causes. The two most common causes of sciatica are herniated disks and bone spurs in the spine that cause the sciatic nerve to become pinched. Other spine conditions that can cause sciatica include: degenerative disk disease, spondylolisthesis, lumbar spinal stenosis, sacroiliac joint dysfunction and piriformis symdrome. Simple muscle spasms in the lower back or buttocks can also cause sciatica. Although rare, pregnancy can cause a herniated disk resulting in sciatica.