Work Environment Affects Rate of Back Injuries

Giving workers more control over their work environment and the ability to make decisions about their work may help prevent low back injury according to a study by researchers at the Johns Hopkins School of Public Health. Body weight in relation to height is also an important modifiable factor. The study appeared in the July, 1999 issue of the American Journal of Public Health.

In an examination of the effects of anthropometric (dimensions of the human body), ergonomic, and psychosocial factors on the risks of sustaining a low back injury, researchers looked at a group of municipal workers in Baltimore, Maryland who performed a wide variety of tasks. The purpose of the study, which used as its basis previous research demonstrating that work-related stress is associated with low back injuries, was to look at all the factors that might contribute to this type of injury within a comprehensive framework.

Researchers studied 274 cases of low back injury from four city departments (education, public works, recreation and parks, and transportation) as recorded in clinic records from March, 1990 to April, 1991. Each patient was matched to two controls who had not sustained injuries. The questionnaire, which trained interviewers went over with both the patients and the control group, covered areas such as work history, work characteristics, work injuries, back pain, psychosocial and work organization, health behaviors and demographics. The work control section delved into the workers' ability to have flexibility, to make decisions, and to exercise creativity. Both case patients and controls described the four most strenuous tasks performed during a typical work day.

Lead author Ann H. Myers, ScD, former faculty member of Health Policy and Management, Johns Hopkins School of Public Health said, "We saw strong association between the risk of low back injury and job strain, the combination of high psychological demands and low control over one's work." Using those with low job strain as the reference group, researchers found that the likelihood of low back injury was 1.7 times as high for those with medium job strain, and 2.1 times as high for those with high job strain.

Co-author Susan Baker, MPH, professor, Health Policy and Management, said, "The major determinant of whether a worker receives a back injury is the task he has to perform. Because cases and controls were matched on the basis of their jobs, we were able to look at the additional effect of personal risk factors such as job strain."

Both researchers noted that workers, safety engineers, and ergonomists who inspected the injury sites were able to suggest strategies and equipment that would reduce the strenuousness of many jobs.

Lower back injuries are the reason for more absence from work than any other injury or disease. In 1992, 792,000 back injuries accounted for 24% of all work-related injuries. Compensation for back injury was higher than for all work-related injuries and in dollar amounts was $36 billion or 31% of total compensation costs.

The study was funded by the national Institute for Occupational Safety and Health, Centers for Disease Control and Prevention and in part by the National Center for Injury Prevention and Control.