Dry Needling to a Key Myofascial Trigger Point May Reduce the Irritability of Satellite MTrPs

This study investigated an important phenomenon in myofascial trigger point therapy: the possibility that treating a key (primary) trigger point may positively influence secondary (satellite) trigger points located within its referred-pain zone. The research was conducted with 14 patients who had bilateral shoulder pain with active trigger points in the infraspinatus muscle on both sides. The study design was particularly clever, using each patient as his or her own control—one side received dry needling while the other side was not treated, allowing for a direct comparison. The dry needling procedure followed established techniques, with needle insertion into the infraspinatus trigger point until local twitch responses were obtained, which are considered essential for treatment success.

Researchers measured several parameters before and immediately after treatment: shoulder internal rotation range of motion (active and passive), shoulder pain intensity, and pressure pain threshold in three different muscles—the infraspinatus (the treated muscle), the anterior deltoid, and the extensor carpi radialis longus (both located within the infraspinatus referred-pain zone). The results were impressive and statistically significant. On the treated side, there was a substantial increase in both active and passive range of motion (55.1% for both), a dramatic reduction in pain intensity (64.8%), and significant increases in pressure pain threshold: 80.2% in the treated infraspinatus muscle, 30.8% in the anterior deltoid, and 18.2% in the extensor carpi radialis longus. Crucially, the untreated (control) side showed no significant changes in any of these parameters, confirming that the observed effects were specific to the treatment.

This finding has important clinical implications. It suggests that trigger points do not function in isolation but rather as part of an interconnected system. When a 'key' trigger point is properly inactivated, it can suppress the activity of 'satellite' trigger points within its referred-pain zone. The proposed mechanism involves central sensitization at the spinal cord level—the primary trigger point sends nociceptive impulses that sensitize dorsal horn neurons, leading to the development of satellite trigger points.

When the primary point is inactivated, this central sensitization is removed, allowing the satellite points to also calm down. The researchers also observed a trend toward improvement on the contralateral side, although it was not statistically significant, suggesting possible systemic effects of treatment. This finding is consistent with observations in acupuncture, where treating a single point can have effects at a distance. The study provides objective evidence for concepts that were previously based primarily on clinical observations, validating the approach of identifying and treating 'key' trigger points as an efficient therapeutic strategy.