Elements of Ergonomics Programs A Primer Based on Workplace Evaluations of Musculoskeletal Disorders

On the recommendation of a State occupational safety and health agency and on the basis of their inspection of certain work conditions, the management of a window manufacturing plant asked NIOSH to evaluate the risk of carpal tunnel syndrome among workers engaged in assembling window units. As part of a medical evaluation, NIOSH investigators reviewed OSHA Form 200 logs and pertinent company medical records and held confidential interviews with workers doing the assembly work. Questions asked during the interviews sought information about the symptoms workers experienced since beginning work at the plant, including the date of onset, location, type, severity and timing (during day or night, steady or intermittent), duration, medical and surgical treatment, past medical history, most difficult job tasks, and hobbies. They also asked for suggestions for changes in assembly procedures or tools used to alleviate apparent problems. The following case definition of work-related carpal tunnel syndrome was adopted in assessing these data:

• During the interview, the worker reported pain, numbness, or tingling affecting the median nerve distribution of the hand(s).

• Symptoms lasted at least 1 week or occurred on multiple occasions.

• Symptoms were severe enough to waken the person from sleep.

• Evidence existed of work relatedness in that the symptoms began after starting work at a job involving recognized risk factors for carpal tunnel syndrome (e.g., repetitive hand movements, excessive force, awkward hand positions, pinch grips, etc.).

A review of OSHA Form 200 logs from over a 3-year period indicated no hand/wrist disorder entries the first year, two entries for hand/wrist pain in the second year, and nine entries for either hand/wrist pain or carpal tunnel syndrome in the third year. As the size of the assembly workforce over the 3-year period remained the same (27 to 28 workers), these data suggested a worsening problem. The medical interviews of all 28 assembly workers indicated five confirmed cases of carpal tunnel syndrome (three surgically treated at the time of the evaluation) and five other possible carpal tunnel syndrome cases. Other health effects included numbness in the ulnar nerve (three workers), ganglionic cysts (two workers), tendonitis (three workers), elbow pain (one worker), neck pain (one worker), and shoulder pain (one worker).

The ensuing ergonomics evaluation of assembly work tasks revealed repetitive hand/wrist manipulations (8 of 12 job tasks requiring 20,000+ movements per shift) with varying degrees of force and bent wrist positions—all risk factors commonly associated with carpal tunnel syndrome. The pressure to increase production and working with defective materials which necessitate using added force to assemble parts were believed to worsen the problem [HETA 88-361-2091].