Trigger point injections are intramuscular injections used to treat muscle pain centering around so-called “trigger points,” irritable knots of taut, non-relaxed muscle fiber. Often these trigger points can be felt as lumps or nodules under the skin. Trigger points may also irritate the nerves around them, causing pain in other parts of the body.

For more information: 

• WebMD.com Article
  
• Spine-Health.com Video