Low back pain is caused by injury to a muscle (strain) or ligament (sprain). Common causes include improper lifting, poor posture, lack of regular exercise, a fracture, a ruptured disc or arthritis. Often, the only symptom is pain in the lower back. Most low back pain goes away on its own in two to four weeks. Physiotherapy and pain relievers can help. A few cases may require surgery.By far the most common cause of lower back pain, mechanical pain (axial pain) is pain primarily from the muscles, ligaments, joints (facet joints, sacroiliac joints), or bones in and around the spine. This type of pain tends to be localized to the lower back, buttocks, and sometimes the top of the legs.