Characteristics of Myofascial Pain Syndrome of the Infraspinatus Muscle

Abstract

ObjectiveTo report the characteristics of myofascial trigger points (MTrPs) in the infraspinatus muscle and evaluate the therapeutic effect of trigger-point injections.MethodsMedical records of 297 patients (221 women; age, 53.9±11.3 years) with MTrPs in the infraspinatus muscle were reviewed retrospectively. Because there were 83 patients with MTrPs in both infraspinatus muscles, the characteristics of total 380 infraspinatus muscles with MTrPs (214 one side, 83 both sides) were investigated. Specific characteristics collected included chief complaint area, referred pain pattern, the number of local twitch responses, and distribution of MTrPs in the muscle. For statistical analysis, the paired t-test was used to compare a visual analogue scale (VAS) before and 2 weeks after the first injection.ResultsThe most common chief complaint area of MTrPs in the infraspinatus muscle was the scapular area. The most common pattern of referred pain was the anterolateral aspect of the arm (above the elbow). Active MTrPs were multiple rather than single in the infraspinatus muscle. MTrPs were frequently in the center of the muscle. Trigger-point injection of the infraspinatus muscle significantly decreased the pain intensity. Mean VAS score decreased significantly after the first injection compared to the baseline (7.11 vs. 3.74; p<0.001).ConclusionCharacteristics of MTrPs and the therapeutic effects of trigger-point injections of the infraspinatus muscle were assessed. These findings could provide clinicians with useful information in diagnosing and treating myofascial pain syndrome of the infraspinatus muscle.

Sonoanatomy and an ultrasound scanning protocol of the intramuscular innervation pattern of the infraspinatus muscle

“…The wide spread of nerve terminals within the IS in the results of this study based on Sihler’s staining support that trigger points can occur at various sites within the muscle. However, the main occurrence site of the trigger point presented in the previous study was mainly the middle part of the muscle 5 14 15. Comparing this with the results from the present cadaver study, it was found that the main trigger point was the muscle belly of the IS.…”

“…In addition, in this study, many intramuscular nerve terminals were observed in the medial third of the IS. Also, according to Kwon et al ,5 since the trigger point is reported to be multiple sites if another injection point is added rather than a single injection point, it is thought that more effective treatment can be promoted in consideration of the spread of BoNT to the surrounding area.…”

“…The most prominent symptoms among them include local and regional muscle pains 1. Specifically, in the shoulder region, the infraspinatus muscle (IS) is the region that is most frequently affected by MPS,2–4 and it frequently harbors myofascial trigger points 5…”

Change in muscle hardness after trigger point injection and physiotherapy for myofascial pain syndrome

“…Because repeated intramuscular injection of local anesthetics results in myotoxicity (49,50), this study used a short-term intervention, 2 weeks of treatment, to compare the effects of SM and TPI treatment. Although prior investigations reported that weekly TPI for 1-2 weeks immediately improved myofascial pain (16)(17)(18)40,51), some studies noted significant decreases in pain scores over 4 weeks after repeated TPI for MTrPs in patients with myofascial pain (43,52,53). Ideally, future studies should assess the effects of repeated TPI and dry needling for longer than 4 weeks on muscle hardness, including the TB.…”

“…Physiotherapy, such as stretching and massage treatment, is the most popular treatment for MPS (5,15), and massage treatment for muscles of MPS patients is considered one of the most effective methods for reducing pain and muscle hardness (9). In addition, the use of the local anesthetic lidocaine in trigger point injection (TPI) of MTrPs reduces localized and referred pain and is a mainstay of short-term MPS management (16)(17)(18). However, the outcomes of these MPS treatments have not been carefully evaluated.…”