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Back Pain Sufferers Vindicated

Award-Winning Study of Muni Drivers Proves Job-Related Back Aches Aren't "All in Your Head"

by Patricia McBroom, Public Affairs
posted December 09, 1998

Muni driver pushing a cable car

Muni cable car crews were found to have three times greater risk of back injury than bus and light rail operators, due to the heavy physical labor of pushing cable cars and pulling mechanical levers.

Back injury at work often gets explained -- and sometimes dismissed -- as a psychological problem. That's because researchers have never been able to prove that the physical demands of the job alone can result in injury to the spine, quite apart from such complications as job dissatisfaction or problems with supervision.

Now, in a prize-winning paper, researchers at the School of Public Health have untangled this perplexing issue for one industry -- the people who drive buses in San Francisco.

They have found that after accounting for all the possible psychosocial causes of back injury, drivers with the San Francisco Municipal Railway (Muni) still have an elevated risk for injury that can be attributed solely to their physical working conditions, particularly the number of hours on the job.

Drivers who worked full-time had more than twice as many back injuries as those who worked part time. In fact, the risk was almost three times as high for full-timers, raising the question of whether part-time work might be effective in reducing workers' compensation claims. Cable car drivers also had three times more back injuries due to the heavy physical work of moving these historic vehicles.

The research, led by Niklas Krause, a physician-epidemiologist and visiting scholar, has been chosen in international competition to receive the Swedish Volvo Award for 1998, given for excellence in clinical studies.

It is being published in the December issue of Spine, the leading international journal in the field. Co-authors are David Ragland, a School of Public Health research epidemiologist; June Fisher, a UCSF clinical professor; and Leonard Syme, Berkeley professor emeritus of epidemiology.

"Although we can't generalize to other work environments, we've been able to prove an important principle," said Krause. "We can show that both physical and psychosocial conditions in the workplace play a role in causing back injury."

The research also revealed that after accounting for physical work load, a stressful job with high psychological demands, low satisfaction and low supervisor support can cause spinal injury.

"In fact," said Krause, "this is one of the first studies to prove that job stress is a cause of low-back injury, even after taking physical and individual factors into account."

Said Syme, a noted authority on workplace stress and chief adviser on the study: "You have stress on the job, stress at home, relations with supervisors, psychological demands and physical demands -- all tied up together. Now for the first time we have been able to sort out these multiple factors and figure out what is really causing the back pain."

The Muni driver study followed subjects for several years, providing rarely obtained information on conditions that pertained before and after the injury.

Researchers followed drivers onto the buses and watched as they padded their broken-down seats with newspapers or sacrificed their breaks to make up for delays on the route. They learned about psychological and social stresses from several questionnaires given to the 1,449 Muni drivers in the baseline study by Ragland, Syme and Fisher, which lasted from 1983 to 1985.

For the current study, Krause gained access to difficult-to-obtain records on workers' compensation and discovered that 320 of those 1,449 drivers had reported a total of 445 back injuries during the five years of observation.

"One driver in five had a back injury and some had more than one. That's a high rate of injury, comparable to the rates for firemen and policemen," said Krause.

He said the spinal injuries cost Muni several million dollars per year in workers' compensation and represent only the tip of an iceberg.

About half the U.S. workforce experiences work-related back pain in any one year, but only a fraction ever report it, he said.

The researchers are currently discussing intervention projects with Muni aimed at reducing the number of back injuries. One such intervention is already providing extra drivers and improved working conditions on the Fillmore bus route. Muni management has also purchased new driver seats for many vehicles and has said it will work with unions and researchers to improve working conditions.


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