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Researchers study effects of carpal tunnel syndrome

man sitting in research chair
November 21, 2008

Grasping an object is as easy as reading a newspaper for most people. It’s a natural function, honed by years of experience. But take away several of the sensory inputs (as happens when a person suffers from carpal tunnel syndrome), and the brain is left grasping at straws in trying to decipher incomplete and “noisy” information from only a portion of its normal inputs (fingers). The result can be a noticeable loss of hand dexterity for the carpal tunnel syndrome (CTS) sufferer.

Help may be on the way for that person thanks to a new five-year, $1 million grant from the National Institutes of Health to a research team led by Marco Santello, an associate professor of kinesiology at Arizona State University.

Santello says the goal of the project is to fill in the knowledge gaps that exist concerning CTS and its effect on hand dexterity. CTS currently affects the quality of life for 6 to 14 million people in the U.S.

“Our main goal is to quantify the effect of CTS on hand control and grasping,” Santello said. “If you have CTS, even in its mild severity, you have problems learning how to control digit (finger) forces as a function of object properties such as weight and texture.”

Santello said that current clinical methods of determining the severity of CTS focus on the state of a person’s median nerve, which conveys sensation from the thumb, index, middle and part of the ring fingers, as well as motor commands to some of the hand muscles. One of the electro-diagnostics tests of the median nerve, where an electrical stimulus is administered to measure how fast the nerve can transmit the stimulus, tells doctors if the nerve is healthy or, alternatively, the extent of its degeneration. But it doesn’t provide information on the person’s ability to control the hand.

“It is difficult to correlate that measurement with a person’s dexterity,” Santello said. “It might say, yes I have mild CTS, but how much does that impact my dexterity, my ability to manipulate?”

This information is important because it could be used to measure the effectiveness of surgical intervention and physical rehabilitation to improve hand function.

Santello explained that a person with CTS might have intact sensory feedback from one and a half of the five fingers on that person’s right hand, for example. But when that person manipulates objects, the brain receives and integrates sensory inputs from all digits engaged in the task, so that movement and forces of the digits can be properly coordinated.

With the majority of the sensory inputs now not properly working, the brain has to compensate for the insufficient data coming to it. Often that means over grasping an object to secure it before picking it up. Over grasping can result in an even greater compression of the median nerve, resulting in greater severity of CTS.

“If you are exerting more force than you need on a daily basis and you are not fully aware of it, it is likely to make CTS worse because you keep adding compression to the nerve,” he said.

The project, which Santello will perform with Dr. Anthony Smith of Mayo Clinic in Arizona and Jamie Johnston of the University of Calgary, will use CTS as a research model to improve the understanding of how tactile, or touch, feedback is utilized by the central nervous system. Santello said it also could provide insight into how electro-diagnostic measures of nerve function relate to specific aspects of grasp control, in turn, improving the interpretability and applications of clinical assessments. Additional support from Mayo Clinic will be provided by Dr. Mark Ross, who will screen and evaluate patients with CTS, and Amylou Dueck, who will assist with the statistical analysis.

Santello added that this project grew out of an ASU-Mayo Clinic seed grant program that began in 2005. The program provides seed funding to teams of ASU-Mayo researchers working together with the goal of moving the project along far enough so to attract major grant funding.

Dr. Keith Kelly, an emeritus member of Mayo Clinic, played a key facilitating role between the Mayo team and Santello’s ASU group. Kelly saw the connections between the two groups and helped foster their relationship.

Santello’s project, which was funded in the first round of ASU-Mayo seed grants, is the first project to secure major federal funding as a result of its involvement in the program. He added that the seed grant program helped move the project along in many ways.

“We collected some important data through the seed grant project and used it in our proposal to the NIH,” he said. “Our pilot data were interesting because they showed some important trends, and in our NIH proposal we said we wanted to do some additional studies and explore additional issues on a larger sample.”