Other potential pain generators include the ligaments which hold the spine together and the muscles which move it. The ligaments, or their attachments to the bone, can be overstretched or partially torn, resulting in a source of inflammation. Muscles can be injured by overstretching or direct trauma. They can also become painful as a result of chronic contraction due to irritation from another source, such as a nerve injury or joint injury. The prolonged contraction can cause changes in the muscle, leaving it shorter and stiffer than normal. Any movement can then further irritate the muscle causing pain. This is called myofascial pain. Discrete trigger points may develop and become self perpetuating sources of pain unless they are treated.