Sep. 25, 1998 UC San Francisco researchers have developed a new animal model to study carpal tunnel syndrome and have shown high pressure to this area in the wrist damages the structure as well as decreases nerve activity.
"This is the first reported animal model to show UC San Francisco researchers have developed a new animal model to study the effects of increased pressure within the carpal tunnel," said Edward Diao, MD, UCSF assistant professor and chief, hand and microvascular surgery, department of orthopaedic surgery. "This model may help us determine how much pressure to the carpal tunnel is too much for humans and further allow us to develop and test treatments for carpal tunnel syndrome."
Diao and UCSF researchers presented their study findings at the annual meeting for the American Society for Surgery of the Hand on September 10.
The carpal tunnel is the space in the wrist where a major nerve, the median nerve, resides, said Diao. The median nerve is vulnerable to injury.
Compression or pressure to this nerve results in pain, numbness or tingling to the fingers -- symptoms of carpal tunnel syndrome. This syndrome may result from repetetive activity of the hands or heavy lifting, he added.
"Carpal tunnel syndrome has become an epidemic," according to Diao. "Over a ten year period, the incidence of reported carpal tunnel syndrome has increased about ten fold."
In the current study, researchers studied carpal tunnel syndrome in sixteen rabbits. Researchers inserted inflatable plastic balloon catheters or tubes into one carpal tunnel of each animal, so that with balloon inflation, the median nerve of the carpal tunnel would be compressed. Balloon pressures comparable to pressures experienced by humans were tested (40mmHg, 50mmHg, 70mmHg, and 80 mmHg). For each animal, an uninflated balloon catheter was inserted into the carpal tunnel of the opposite side as the control.
Researchers measured the time it took for carpal tunnel syndrome to develop by examining nerve activity in each animal. Similar to nerve conduction studies on humans with this condition, a delay in nerve activity or loss of nerve activity indicates carpal tunnel syndrome.
Study findings showed the higher the pressure, the less time required for carpal tunnel syndrome to develop.
Researchers also examined the structure of the median nerve and compared it with that of the controls. Researchers found damage to the compressed nerve -- a decrease in the number of nerve fibers and average nerve fiber diameter was reduced. In addition, the thickness of tissue surrounding the nerve increased with increased pressure.
This type of damage in the human nerve, said Diao, will result in loss of sensibility of the fingers and cause pain and irritability of the nerve. Depending on the severity of the damage, these changes may be permanent. "Once the model is fully validated, we can test how good the treatments are in preventing the occurrence of carpal tunnel syndrome or increasing the amount of time that one can tolerate increased pressure before these changes occur," said Diao.
Future studies with this model, he said, will also look at reversing carpal tunnel syndrome.
Co-authors of the study are Shin-Ichi Hida, MD, assistant professor of medicine at Fukuoka University in Japan; Rajiv Das, MD, MPH UCSF postdoctoral fellow in occupational and environmental medicine; Masatoshi Yamada, MD, PhD, UCSF research fellow in the department of orthopaedic surgery; Ellen Liebenberg, UCSF senior staff research associate, orthopaedic bioengineering laboratory, department of orthopaedic surgery; Jeffrey Lotz, Phd, UCSF assistant professor and director of orthopaedic bioengineering laboratory, department of orthopaedic surgery; and David Rempel, MD, UCSF assistant professor of medicine and director of UCSF-UC Berkeley ergonomics program.
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