Trigger Point Injections in St. Louis

A trigger point is a small, tightly contracted band within a muscle that will not relax. It is tender to direct pressure and characteristically refers pain elsewhere; a trigger point in the upper trapezius commonly refers into the head and neck. Left untreated, the surrounding muscle guards against the pain, which tightens the band further.

A fine needle is placed directly into the taut band and a small volume of local anesthetic is injected. The mechanical effect of the needle together with the anesthetic interrupts the spasm and pain cycle, allowing the muscle to lengthen. Ultrasound guidance is used where the target sits near a nerve, a blood vessel or the chest wall.

Myofascial pain of the neck, shoulders, upper back and lumbar paraspinal muscles responds best. Trigger point injections are also used alongside other treatments when muscular guarding is limiting progress in rehabilitation, including after a motor vehicle injury.

The injection takes only a few minutes and several points can be treated in a single visit. Soreness at the injection site for a day or two is normal. Patients are encouraged to stretch the treated muscle gently afterwards, since the aim is to restore length rather than simply numb the area.

The prevailing explanation is the integrated hypothesis, which locates the problem at the motor endplate. Excessive acetylcholine release causes a small cluster of sarcomeres to remain contracted. Because they cannot relax, they compress the capillaries supplying them, which cuts off the oxygen and ATP that muscle needs in order to release the contraction. The contraction sustains the ischemia and the ischemia sustains the contraction.

That local hypoxic environment accumulates bradykinin, substance P, CGRP and hydrogen ions, all of which sensitize local nociceptors. This is why an active trigger point is exquisitely tender out of proportion to its size, and why pressing it reproduces the patient recognizable pain rather than simply hurting.

Trigger points refer pain in patterns that do not follow dermatomes, which is a common source of diagnostic confusion. The referral arises centrally: sustained nociceptive input from the muscle sensitizes dorsal horn neurons that also receive input from other territories, and the brain misattributes the origin. Because the convergence pattern is anatomically consistent, the referral maps are reproducible between people, which is what makes them clinically useful.

It also explains why treating only where the patient feels pain often fails. The upper trapezius refers into the temple, the gluteus minimus down the leg in a pattern resembling sciatica. Treating the site of the sensation rather than the site of the trigger point is a common reason these problems persist for years.