Sacroiliitis is an inflammation of one or both of your sacroiliac joints - situated where the lower spine and pelvis connect. This can cause pain in the lower back and extend down one or both legs. It is commonly caused by degenerative arthritis, traumatic injury, motor vehicle accident, or blow to the buttock or pelvic region.
Sciatica, or sciatic neuritis, is pain which radiates alone the sciatic nerve, which runs down one or both legs from the lower back. It's usually caused when a herniated disk or bone spur in the spine presses on the nerve.
Pain originates in the spine and radiates down the back of the leg. Sciatica typically affects only one side of the body.
Medication for pain and physical therapy are common treatments.