Trigger point injection (TPI) may be an option for treating pain in some patients.

TPI is a procedure used to treat painful areas of muscle that contain trigger points, or knots of muscle that form when muscles do not relax.

Many times, such knots can be felt under the skin.

TPI is used to treat many muscle groups, especially those in the arms, legs, lower back, and neck.

In addition, TPI can be used to treat fibromyalgia and tension headaches.

The technique is also used to alleviate myofascial pain syndrome (chronic pain involving tissue that surrounds muscle) that does not respond to other treatments.