Claim rates of compensable back injuries by age, gender, occupation, and industry. Do they relate to return-to-work experience?

STUDY DESIGN: A retrospective cohort study of Michigan workers' compensation cases involving back injuries in 1986 and 1987 with incidence and outcome data.

OBJECTIVE: To determine claim rates by age, gender, and industry or occupation for compensable back injuries and to investigate the relation between occupation and return to work.

SUMMARY OF BACKGROUND DATA: The cohort of 24,094 Michigan workers' compensation cases from 1986 and 1987 in which claimants were compensated for back injuries was reviewed. Compensation eligibility requires more than 7 days' disability after injury.

METHODS: Claim rates for back injuries by age, gender, and industry or occupation using employment data interpolated from 1980 and 1990 Census 1% Public Use Microdata Samples. Cox proportional hazards analysis was performed for return to work in the first 8 weeks after injury, with occupation coded at the three-digit level.

RESULTS: All-age claim rates for Michigan compensable back injuries by occupation ranged between 0.03% and 1.7% annually (0.39% for all cases) and were generally higher in women in white collar occupations and in men in blue collar occupations. The claim rate peaked in men in the 25-34 year range, with the highest rates in manual labor occupations. The peak claim rates by age were less marked in women, tending to occur broadly throughout the 25-44-year range. Similar all-age values were recorded by industry. The male-to-female risk ratio over all occupations does not vary by age and is approximately 1.4:1. As the classification of occupation became more detailed, large differences in risk were documented within major occupation groups. The highest risk in this study was approximately 6% annually for 25-44 year old men in driver-sales (beverage truck drivers and delivery workers). Only 7 of 40 occupation categories showed a significant relative hazard for return to work in the first 8 weeks after injury, and these were blue collar occupations with earlier return than the reference sales category. For Michigan compensable back injuries, a rough estimate of the true annual incidence of new claims is 94% of the reported claim rate.

CONCLUSIONS: The relative risk of compensable back injury is generally higher for females in white collar occupations, higher for males in blue collar occupations and approximately equal in service occupations. Although the risk of back injury is related to occupation, the same occupational factors do not operate as a barrier to return to work.