Prolotherapy, which has been used since the 1950s, is based on the theory that chronic pain is often caused by the laxness of the ligaments responsible for keeping a joint stable. When these ligaments and associated tendons become loose, the body is believed to compensate by using muscles to stabilize the joint. The net result, according to prolotherapy theory, is muscle spasms and pain. Prolotherapy involves injections of chemical irritant solutions into the areas around the ligaments. These solutions are believed to cause tissue to grow quickly, which would increase the strength and thickness of the ligaments. This presumably tightens the joint and relieves the burden on associated muscles, stopping muscle spasms. Prolotherapy is used to treat many conditions, including back pain, osteoarthritis, fibromyalgia, plantar fasciitis, sciatica, sports injuries, temporomandibular joint disorder (TMD), tendinitis, and tension headaches.