High prevalence of shoulder girdle muscles with myofascial trigger points in patients with shoulder pain

Abstract

Background: Shoulder pain is reported to be highly prevalent and tends to be recurrent or persistent despite medical treatment. The pathophysiological mechanisms of shoulder pain are poorly understood. Furthermore, there is little evidence supporting the effectiveness of current treatment protocols. Although myofascial trigger points (MTrPs) are rarely mentioned in relation to shoulder pain, they may present an alternative underlying mechanism, which would provide new treatment targets through MTrP inactivation. While previous research has demonstrated that trained physiotherapists can reliably identify MTrPs in patients with shoulder pain, the percentage of patients who actually have MTrPs remains unclear. The aim of this observational study was to assess the prevalence of muscles with MTrPs and the association between MTrPs and the severity of pain and functioning in patients with chronic non-traumatic unilateral shoulder pain.

Methods: An observational study was conducted. Subjects were recruited from patients participating in a controlled trial studying the effectiveness of physical therapy on patients with unilateral non-traumatic shoulder pain. Sociodemographic and patient-reported symptom scores, including the Disabilities of the Arm, Shoulder, and Hand (DASH) Questionnaire, and Visual Analogue Scales for Pain were compared with other studies. To test for differences in age, gender distribution, and education level between the current study population and the populations from Dutch shoulder studies, the one sample T-test was used. One observer examined all subjects (n = 72) for the presence of MTrPs. Frequency distributions, means, medians, standard deviations, and 95% confidence intervals were calculated for descriptive purposes. The Spearman's rank-order correlation (ρ) was used to test for association between variables.

Results: MTrPs were identified in all subjects. The median number of muscles with MTrPs per subject was 6 (active MTrPs) and 4 (latent MTrPs). Active MTrPs were most prevalent in the infraspinatus (77%) and the upper trapezius muscles (58%), whereas latent MTrPs were most prevalent in the teres major (49%) and anterior deltoid muscles (38%). The number of muscles with active MTrPs was only moderately correlated with the DASH score.

Conclusion: The prevalence of muscles containing active and latent MTrPs in a sample of patients with chronic non-traumatic shoulder pain was high.

Figure 1

Referred pain patterns (red) from the upper and lower trapezius muscle MTrPs (Xs), according to Simons et al. Illustrations courtesy of LifeART/MEDICLIP, Manual Medicine 1, Version 1.0a, Lippincott, Williams & Wilkins, 1997.

Figure 2

Referred pain patterns (red) from the upper and middle trapezius muscle MTrPs (Xs), according to Simons et al. Illustrations courtesy of LifeART/MEDICLIP, Manual Medicine 1, Version 1.0a, Lippincott, Williams & Wilkins, 1997.

Figure 3

Referred pain patterns (red) from the anterior deltoid muscle MTrPs (Xs), according to Simons et al. Illustrations courtesy of LifeART/MEDICLIP, Manual Medicine 1, Version 1.0a, Lippincott, Williams & Wilkins, 1997.

Figure 4

Referred pain patterns (red) from the infraspinatus muscle MTrPs (Xs), according to Simons et al. Illustrations courtesy of LifeART/MEDICLIP, Manual Medicine 1, Version 1.0a, Lippincott, Williams & Wilkins, 1997.

Figure 5

Flow chart showing a schematic summary of patient participation in this study.

Figure 6

The number of active (black bar) and latent (grey bar) of MTrPs per subject. The X-axis shows the number of subjects, and the Y-axis shows the number of MTrPs per subject (n = 72).

Figure 7

The number of subjects with active (black bar) or latent MTrPs (gray bar) per muscle. The X-axis shows the muscles that were examined for identification of MTrPs, and the Y-axis shows the number of subjects with MTrPs (n = 72).

Figure 8

Scatterplot of DASH scores versus the number of muscles with active MTrPs. The regression line shows a weak positive correlation (r = 0.3), indicating that increasing numbers of active MTrPs have only a moderate effect on DASH scores.