Research Review by Dr. Shawn Thistle©


May 2007

Study Title:

Dry needling to a key myofascial trigger point may reduce the irritability of satellite MTrPs


Hsieh Y-L et al.

Publication Information:

American Journal of Physical Medicine and Rehabilitation 2007; 86: 397-403.


Myofascial Trigger Points (MTrPs) have been defined as: a hyperirritable (hypersensitive) spot in a taut band of skeletal muscle fibres. The concept of MTrPs is familiar to most manual therapists, and there are a variety of treatments commonly used to treat them. It is generally accepted that there are two types of MTrPs:
  1. Active Trigger Points - are a recognized source of pain to the patient, exhibit a local twitch response (LTR - see below) to direct touch or stimulation, and refer pain to a characteristic location
  2. Latent Trigger Point - generally not recognized as a source of pain until directly palpated/stimulated, at which time can become exquisitely tender
Latent MTrPs can convert into active MTrPs, and vice-versa.

Contemporary evidence has added a new level of understanding to the pathology of MTrPs. Recent animal studies suggest that the LTR is a spinal cord-mediated reflex. LTR represents a burst of motor endplate activity which can be palpated as a twitch in the muscle. Areas that exhibit LTR have been shown to contain a greater concentration of nociceptive nerve endings, and are normally found in the muscle's motor endplate zone. Further, increased end plate noise is more common at MTrP sites than other parts of skeletal muscles.

In humans, stimulation of a LTR locus can cause pain (low-pressure), referred pain (moderate-pressure), and a LTR (high-pressure). When an MTrP is very sensitive however, any level of stimulation may elicit referred pain and a LTR. Further, it is thought that there is an intimate relation between primary (key) MTrPs and satellite (or secondary) MTrPs in the zone of pain referral. The purpose of this study was to evaluate whether dry needling at a primary MTrP was effective at reducing sensitivity and pain at satellite MTrPs in the area of pain referral.

Previous evidence suggests that dry needling can be effective for relieving pain caused by MTrPs. Dry needling involves using a sterile acupuncture or hypodermic needle which is inserted into a trigger point, without injecting any anesthetic. The goal of this technique is to elicit a LTR. This process is generally repeated until the LTR ceases, at which time the TrP is thought to be "deactivated".

This study was conducted in a single-blinded manner, and involved 14 patients (average age ~ 60) with bilateral shoulder pain who had active MTrPs in the infraspinatus muscle. Each patient received dry needling in a randomly selected side, with the other side serving as a within-subject control. Outcome measures were performed bilaterally before and after treatment, and included shoulder ROM (internal rotation), pain intensity in the shoulder (measured by Visual Analogue Scale), and pressure-pain threshold in MTrPs of the infraspinatus, anterior deltoid, and extensor carpi radialis longus [ECRL] (the latter two muscles are common secondary pain sites from infraspinatus TrPs). Pain-pressure threshold was measured with an algometer.

Inclusion/Exclusion criteria included:
  • patients had to have bilateral shoulder pain without treatment other than oral pain medication for the last 3 months
  • patients had active TrPs in the infraspinatus on both sides
  • patients had no contraindication to dry needling (ex. infections, recent multiple trauma, pregnancy, etc.)
  • no previous surgery to the neck or upper limb
Dry needling was performed for one session using a 5-ml syringe with a #25 hypodermic needle. Once inserted into the infraspinatus TrP, the needle was rapidly moved (pistoned) in the TrP until the LTR stopped - this process generally took 1-2 minutes.

Pertinent results of this study include:
  • there were significant increases in both active and passive ROM in the treated shoulder compared to the untreated shoulder (p<0.01)
  • pain relief was significantly greater in the treated side than untreated side (p<0.001)
  • there were significant increases in pressure-pain threshold (p<0.01) in the active TrPs in the infraspinatus, as well as the satellite TrPs in the anterior deltoid and ECRL in the treated side, with no significant changes noted on the untreated side

Conclusions & Practical Application:

This small study demonstrated immediate increases in ROM, decreased pain, and increased pain-pressure thresholds in MTrPs in the infraspinatus, anterior deltoid, and ECRL in patients with bilateral shoulder pain after dry needling of the key TrP (infraspinatus). The subjects served as their own control group, so it is worth noting that all of these improvements were statistically significant on the treated side only. There was a small trend of improvement on the non-treated side, which may be attributed to treatment effects, or repeated measures of the study outcomes. This potential effect requires further study.

These findings support the concept that primary MTrPs can influence satellite MTrPs, while providing further evidence that dry needling is an effective treatment for pain and dysfunction related to MTrPs. For therapists that do not utilize acupuncture, other methods of addressing MTrPs (ischemic compression etc.) may also be beneficial as no one treatment has been shown to be superior in treating MTrPs.

Some obvious limitations of this study should be mentioned:
  • no true control group was used
  • follow-up time was severely limited, including only immediate post-treatment responses
  • no comparison treatment or placebo treatment was used for comparison - raising the possibility of non-specific findings
  • the study group was relatively small, and very specific regarding inclusion criteria
Despite these shortcomings, small studies like this are important for providing a basis for future studies. Subsequent research should examine whether similar relationships exists between primary and satellite TrPs in other body regions, as well as which needling techniques are most effective for treating them. Longer follow-up periods and perhaps multiple treatments should also be used.

Manual therapists who practice traditional or medical acupuncture, as well as dry needling are eagerly awaiting well-designed studies to help guide practical application of these techniques.