Kneeling, standing on the job boost arthritis risk

By Anne Harding

NEW YORK (Reuters Health) - Men who spend significant amounts of time kneeling on the job are at great risk of developing osteoarthritis of the knee, a new study published in the American Journal of Industrial Medicine confirms.

While several studies have suggested that people working in jobs that require spending time on one's knees, such as floor laying, are prone to knee osteoarthritis, few have been able to quantify the amount of time spent kneeling that actually increases risk, Dr. Alfred Franzblau of The University of Michigan School of Public Health in Ann Arbor and colleagues note.

Franzblau and his team evaluated 1,970 people participating in the Third National Health and Nutrition Examination Survey for whom knee X-rays were available, limiting their analysis to people who had been on their longest-held job for at least five years.

The researchers had five ergonomics experts rate occupations based on how much time a worker would spend each day sitting, standing, walking or running, carrying or lifting loads greater than 22 pounds, kneeling, or working in a cramped space. This information "allows us to better identify the magnitude of the exposure that contributes to risk," Franzblau told Reuters Health in an interview.

Men in occupations requiring the most kneeling were more than three times as likely as those who spent the least time on their knees to develop knee osteoarthritis, the researchers found. Heavy lifting also nearly tripled knee osteoarthritis risk for men. For women, spending more time standing during the workday increased the risk of knee osteoarthritis.

Based on these findings, the researchers estimate that 21 percent of symptomatic knee osteoarthritis cases in men are due to working in jobs that require kneeling for more than 14 percent of the workday. Thirty-one percent of men in the study had jobs that met this description, including nursery or farm work or construction trades.

While just 5 percent of women in the study had jobs that required kneeling, 35 percent had jobs that required them to stand for more than 30 percent of their work day, in activities such as operating machines or working in sales, the researchers note. This means about 19 percent of cases of symptomatic knee osteoarthritis in women are due to working in such jobs.

"Our results indicate that modifications to work methods are needed to reduce occupational risk of knee osteoarthritis," Franzblau and his colleagues conclude.

SOURCE: American Journal of Industrial Medicine, January 2008.