A complicated system of ligaments and muscles serves to control movement, maintain posture, and support the lower back and pelvis. The muscular system of the lower back is complex, and includes the deep erector spinae or paraspinal muscle groups that run parallel to the spine. There are also larger and more superficial muscles that help to move and protect the lower back. The lower back and abdominal muscles work together with the ligaments to provide movement, stability, and postural support to the lower back and abdominal area. The larger superficial muscles help move and stabilize the lower back. The deeper spinal muscles can be multisegmental, connecting and attaching to more than one vertebra or muscles that support, stabilize and move one segment in relation to another. When lumbar or spinal motion is pushed to the extreme, such as in a car accident, these ligaments and muscles can be damaged. Muscle damage strain or muscle spasm can produce pain, soreness, loss of motion, and if severe enough joint instability. Irritation or injury of the structures of the spine may produce spasm and pain of the muscles of the back and buttock areas. One muscle that is often involved in back problems is the piriformis. It is located in the buttock area and may become painful, sore and go into spasms with nerve, disc, and low back or sacroiliac joint irritation. Unfortunately, the sciatic nerve passes beneath the piriformis and can be compressed when the piriformis is irritated. This can cause symptoms that radiate into the legs. Injury to the lumbar spine can cause weakness, spasm, or tightness of the muscles of the lower back and can result in pain, decreased ability to maintain good posture, limitation in movement and instability of the back.