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This study presents the results of analyses performed to generate hypotheses concerning the general patterns of risk factors for occupational sprains and strains, using Ontario workers' compensation data housed in the Workplace Health and Safety Agency (WHSA) data base. Historically, the largest percentage of lost-time injuries in Ontario, Canada, have been sprains and strains. In 1990, there were 171,047 compensated lost-time injuries with a known nature of injury, of which 50.43% were sprains and strains. From cross-tabulations, a number of statistics such as odds ratios (ORs), 95% confidence intervals, P values, attributable risks and number of injuries attributable, were calculated. Results indicate that occupational sprains and strains are related to the time of the day and, in particular, time into the workshift. They occur more frequently than expected (based on the occurrence of non-sprain and non-strain injuries) in the morning hours and in the first 4 hours of the workshift. They are not found to be related to the starting or ending time or the length of the workshift. They occur more frequently than expected during the early part of a week, especially on Mondays, and the early part of a year (January to May). With respect to age, workers 30 to 59 years old have an increased risk of sprains and strains, whereas workers less than 30 years of age, or 60 or more years of age, have a decreased risk. Workers who are not single, and female workers, have a higher risk of sprains and strains than expected. With respect to occupations, nurses and truckers have a higher-than-expected risk. A number of work environments and activities, such as overexertion, bodily reaction from involuntary motions, running and stretching, and slippery surfaces, are associated with a high risk of occurrence of sprains and strains. These results suggest that significant reduction in the number of occupational sprains and strains could be achieved by targeting prevention programs to reduce excess risks encountered in the first 4 hours of the workshift, on Mondays, and during the first 5 months of the year, and by workers 30 to 59 years of age, female workers, and nurses and truck drivers. It is estimated that, with proper interventions to avoid sprains and strains, a large percentage of sprain and strain injuries could be avoided each year: ie 82.49% of injuries due to bodily reaction from involuntary motions, 89.43% of overexertions in lifting objects, 84.64% of running, stretching, and related injuries, and 76.64% of injuries resulting from loss of balance on slippery surfaces. This study uses an internal comparison, ie comparing the risk of sprains and strains to the risk of all other injuries for various risk categories of interest. As a result, an increased OR may mean an increased risk of sprains and strains, or it may mean a decreased risk of all other injuries for a particular risk category. There are also limitations in the use of workers' compensation data base for epidemiologic studies. Therefore, findings in this study are only suggestive for further investigations and should await confirmations before prevention programs are designed.