Trigger point injections (TPI) are used to treat extremely painful areas of muscle where a knot or tight ropy band of muscle forms when a muscle fails to relax. A trigger point, which can be felt under the skin, may twitch and irritate surroundming nerves that will cause pain to be felt in another part of the body. This can cause scar tissue, limited range of motion, and weakness. An injection of a local anesthetic to the trigger point will stop the pain from occurring.