My sister has chronic headaches that seem to be connected with neck and shoulder muscle tension. She’s going to try something called trigger point injections. What are these? How do they work?

A trigger point (TrP) is an area of hyperirritability within a taut band of muscle. When pressed or palpated these points create a pattern of local and referred pain. Referred means the pain occurs at quite a distance from the points of local tenderness.

Trigger points may be either active (they cause pain at rest or with activity of the involved muscle) or latent. Latent means they are not painful but cause loss or movement and muscle weakness. A latent trigger point may become active in the presence of an acute, sudden overload of the muscle or a more chronic strain.

Trigger point injection involves injecting a numbing agent combined with a steroid drug into the trigger point area. In some cases, the treatment uses dry needling (nothing injected) or the injection of an inert (not active substance) such as saline (salt solution). The treatment goal is to reduce pain and improve movement and function.

The mechanism for how or why trigger point therapy works remains a mystery. It makes sense that injecting a numbing agent into an area of pain would reduce the pain. But there are studies showing that just placing a needle in that same spot and twisting the needle (a form of dry needling) works just as well.

There is no numbing agent involved, so there must be a different mechanism by which this treatment is effective. Some experts suggest that the nervous system reponds to the noxious (painful) stimulation of the needles in a way that shuts down other (chronic) pain messages to the brain.