Understanding the Biophysics of Pain

Siddhartha Sikdar

According to a recent report by the Institute of Medicine, the economic impact of the burden of pain in terms of lost productivity in 2010 was approximately $300 billion. Millions of Americans suffer from chronic pain, which can often be localized in soft tissues such as the ligaments, muscles, and fascia.

Patients with back or neck pain complain of trigger points or muscle knots, which are hard, painful nodules. These irritable nodules are often associated with referred pain, but not always. The reason why some hard nodules are spontaneously painful and others are not is unknown.

It is also not known why and how these trigger points form and what role they play in the pain syndrome. A major impediment to research on this topic has been the fact that these trigger points are diagnosed based on a subjective physical exam. Also, the only information that physicians have about pain severity involves the self-assessment from the patients themselves, which is notoriously nonquantitative. “Doctor, my neck pain on a scale of 1 to 10 is an 11!”

Most people avoid problems that are the “pain-in-the-neck” variety. But Mason bioengineer Siddhartha Sikdar has sought them out. Working with College of Health and Human Services professor and clinician Lynn Gerber, he has developed a method to quantitatively characterize these trigger points.

“By using ultrasound techniques, we have a developed a noninvasive and easily accessible method to objectively describe trigger points,” says Sikdar, an assistant professor of bioengineering and electrical and computer engineering in the Volgenau School of Engineering.

As shown on the figure below, a variation of ultrasound called elastography measures the stiffness of soft tissues by assessing regional tissue compression in response to an applied vibration. The more compression, the less stiff the tissue.  Another potentially important factor for the trigger point is regional blood flow, which can also be readily determined through Doppler ultrasound.

This image shows a variation of ultrasound called elastography, which measures the stiffness of soft tissues. Photo courtesy of the Department of Bioengineering.

While the research will address fundamental questions about the biophysical nature of trigger points, it also has translational/clinical implications. Specifically, the work will help develop objective and quantitative diagnostic metrics for assessing various therapeutic strategies.

The effort is supported by a four-year, $1.974 million R01 grant from the National Institutes of Health (NIH) led by Sikdar. Colleagues who are contributing to the research effort include Gerber; Nadine Kabbani, assistant professor of molecular neuroscience in Mason’s Krasnow Institute for Advanced Study; Saleet Jafri of Mason’s School of Systems Biology, whose area of expertise is bioinformatics and computational biology; William Rosenberger, chair of the Department of Statistics; and Jay Shah, a physiatrist and staff clinician at NIH.

This article originally appeared in the fall 2012 issue of the Bioengineering at Mason newsletter.

To read more stories about Mason, check out the university’s News site.

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