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Biomedical Imaging and Instrumentation

Biomedical Imaging and Instrumentation - Poster Session A

Poster F10 - Association between trapezius muscle thickness and the pressure pain threshold of patients with chronic neck pain

Thursday, October 24, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Chronic pain, defined as pain lasting longer than three to six months, necessitates understanding neurophysiology for effective treatment [1]. It affects approximately 20% of adults in the United States and becomes more prevalent with age [2]. The trapezius muscle is a crucial structure for postural, cervical, and upper limb control and is a common site for chronic pain. However, despite the prevalence of this condition, the tissue-level origins of chronic pain remain unclear. Recent evidence suggests that the thickness of the trapezius muscle may be an important factor behind the manifestation of pain [3]. However, the relationship between trapezius muscle thickness and standard assessments of pain has not been well established. The pressure pain threshold (PPT) is a quick, objective clinical measure of deep muscle tissue’s sensitivity to pain. It is quantified as the minimum amount of pressure applied that causes pain [4] and is a common assessment for myofascial trigger points often found in the trapezius muscle. Muscle thickness may influence the resilience of muscle tissue to pressure-induced pain, but this association has not been investigated for patients with chronic myofascial neck and back pain. The purpose of this study was to explore the association between the trapezius muscle thickness and PPT, using ultrasound imaging techniques and algometry. We hypothesized that increased muscle thickness would be associated with higher PPT values.

Materials and

Methods:  Forty-three adults participated in the study, divided into three groups: individuals with spontaneous pain (the active group, N = 17), individuals with elicited pain (the latent group, N = 15), and individuals without pain (the control group, N = 11). We measured trapezius muscle thickness on both the left and right sides using ultrasound imaging. A trained clinician marked the skin over the trapezius to be imaged after palpating the tissue and identifying any myofascial trigger points. We then imaged the tissue both superior and inferior of this mark in 1cm increments for a total of 10 images. For consistency in this analysis, we chose to use the two images closest to the marking. For each image, we used ImageJ to measure the number of pixels between the skin surface and the superior fascia line bordering the trapezius and converted the thickness measurement to millimeters using a 2cm calibration mark on each ultrasound image. We used an algometer to measure the pressure pain threshold (PPT) four times over both the left and right sides of the trapezius muscle. The algometer applied pressure at the trigger point identified by the clinicians and participants were instructed to indicate when the applied pressure became painful. We compared the average muscle thickness measurements with the average PPT values for each side of a participant. We used a Pearson correlation to identify any significant relationships (α = 0.05).

Results, Conclusions, and Discussions: For all participants, we found a significant correlation between muscle thickness and PPT (Left side: r = 0.373, p = 0.014. Right side: r = 0.378, p = 0.014). Thicker trapezius muscles were associated with higher PPT values, suggesting that muscle thickness may provide greater resilience to pressure-induced pain. This study is ongoing, and we are currently blinded to the groupings of the participants. However, these preliminary findings highlight the potential importance of muscle thickness in chronic pain assessment. Thicker muscles may provide better musculoskeletal support and a higher threshold for pain, which is well aligned with clinical recommendations for muscle strengthening as a tool for managing chronic pain. Future studies will explore additional factors influencing the relationship between muscle thickness and pain sensitivity, such as the effect of body mass index and physical activity levels. Longitudinal studies could also provide insights into changes in muscle thickness and PPT over time, contributing to a more comprehensive understanding of chronic pain mechanisms and management strategies. We believe that better understanding the relationship between muscle thickness and pain threshold could offer valuable information for developing targeted interventions to enhance muscle health and reduce pain sensitivity in individuals suffering from chronic myofascial pain. These findings can potentially improve clinical outcomes through personalized pain management strategies that focus on muscle health.

Acknowledgements (Optional):  This project was supported by the Department of Public Health and the Department of Bioengineering at George Mason University. Funded by NIH HEAL 1R61AT012286 and the Office of Student Creative Activities and Research at George Mason University. We thank A. Aher , M. Jirsaraei, M. Lamarre for assistance with data collection.