Vibration studies target hand and arm injuries

Findings can aid in treatment, prevention

The industrial revolution brought with it a world of positive changes, but among the negative by-products was a slew of new occupational injuries. For example, as far back as 1911, scientists associated vibration from hand-held tools with the risk of pain, numbing, and blanching of the fingers, known as vibration white finger. Although limited progress has been made in reducing this risk over the years, many key aspects of the problem still are not well understood, hampering further efforts to identify worker populations at risk, and to design effective control measures.

The National Institute for Occupational Safety and Health (NIOSH) is pursuing studies to help fill those critical gaps and point to ways for effectively reducing risks of hand-vibration disorders for employees who use jackhammers, chipping hammers, power drills, and other vibrating tools. Individually, the studies focus on particularly complex, challenging areas where new data will further advance the understanding and prevention of job-related hand-vibration disorders. Collectively, the studies constitute a balanced, interlocking program of strategic research.

"White finger occurs more frequently in colder climates, and it works in concert with the vascular constriction associated with colder temperatures," explains Aaron Schopper, PhD, of the NIOSH Health Effects Laboratory Division in Morgantown, WV. "It also affects people who work in refrigerated areas. And in the U.K., for example, they have had a big problem with miners." In addition, says Schopper, individuals who work with hand-held tools are subject to cumulative trauma syndrome (CTS), and occasionally might find problems with elbow joints or shoulders.

What are the greatest risks?

It is difficult to ascertain the precise impact of this type of injury in the United States, says Schopper, because they do not appear in OSHA logs as recordable disorders, "But if you look at the statistics in the United Kingdom, you would figure there certainly is apt to be significant concern here."

The NIOSH studies will give scientists better insight into the factors that link occupational exposures to vibration with given physiological outcomes: How is the energy from a vibrating handle transmitted into the hand and arm? What effects result? By combining this better understanding of physiological health effects with epidemiological data showing trends in the occurrence of cases, scientists will have greater ability to predict types of occupations, work activities, and work settings that may pose the greatest risk of hand-arm vibration disorders. Current projects at NIOSH include:

Using advanced microscope technologies to determine if adverse effects from vibrating tools can be predicted from physical changes in the capillaries at the base of the fingernail cuticle, too small to see with the naked eye. If such changes were discerned, says Schopper, "you would definitely want to consider administrative responses, such as finding the employee some other place to work or a job at which they could work." Limiting exposure to vibration, he says, is the bottom line. For particularly high-vibration frequencies, for example, some types of anti-vibration gloves can be used to reduce exposure.

Developing a computer model of stress and strain on the fingertips from vibrating tool handles, as measured by the degree to which the soft tissues of the fingertips are compressed or displaced by the vibrating handle, as another potential way to flag early warning of adverse effects.

Assessing infrared thermal imaging of the hands as a potential method for identifying the presence and severity of hand-arm vibration syndrome: (A detailed description of hand-arm vibration syndrome can be found at www.labor.state.ak.us/lss/pads/hand%2Darm.htm.)

Designing a test method for simultaneously measuring the impact of a chipping hammer bit and the degree of vibration from the handle. The method would give scientists a way to determine if control measures effectively minimize vibration without diminishing the chipping hammer’s performance.

Investigating the effectiveness of anti-vibration gloves through tests using an instrumented vibrating handle that simulates specific tools and vibration characteristics.

Letting this condition go untreated for an extended period of time is no laughing matter, says Schopper. "You will develop tingling and numbness, similar to what you feel when you use a weedwhacker," he explains. "That’s the sensory-neural part of it. Then there is thermal sensation to some extent, and the ability to detect vibration is degraded. Longer term, you get the symptoms for white finger disease."

This was a particular problem with forestry workers using chain saws, but the advent of shock absorbers has improved conditions. "In U.S. rock quarries in the early days, it was even possible for vascular deterioration to result in gangrene," notes Schopper. While that’s highly unlikely today, it could still happen if an employee totally ignored his symptoms. "But it can take 15 years or more to get to that point," he notes.

For more information, contact: Aaron Schopper, PhD. Telephone: (304) 285-6171. E-mail: aws0@cdc.gov.