Impact of occupational mechanical exposures on risk of lateral and medial inguinal hernia requiring surgical repair.

OBJECTIVES

We undertook a register-based cohort study to evaluate exposure-response relations between cumulative occupational mechanical exposures, and risk of lateral and medial inguinal hernia repair.

METHODS

Among all men born in Denmark between 1938 and 1988, we established a cohort comprising those aged 18-65 years of age, who had at least 1 year of full-time employment between 1993 and 2007. Using information from a Job Exposure Matrix based on expert judgement and year-by-year information on Danish International Standard Classification of Occupations codes for each individual since 1993, we established time-varying cumulative estimates of exposure to daily lifting activities and standing/walking. Cumulative exposures for lagged 5-year time windows were expressed in a way that corresponds to the pack-year concept of smoking (ton-years, frequent-heavy-lifting years, and standing-years). First-time inguinal hernia repairs in the period 1998-2008 were identified in the Danish Hernia Database. We used a logistic regression technique equivalent to survival analysis, adjusting for age, socioeconomic status, region of residence and calendar year.

RESULTS

Within the cohort of 1 545 987 men, we identified 22 926 lateral, 15 877 medial and 1592 pantaloon or unspecified first-time inguinal hernia repairs. The risk of lateral hernia repair increased with ton-years, frequent-heavy-lifting-years, and standing-years, with ORs of up to around 1.4. The exposures correlated, but standing-years remained as the most robust risk factor after adjustment for lifting exposures. In general, the risk of medial hernia repair was unrelated to the exposures.

CONCLUSIONS

Our findings suggest an increased risk of lateral inguinal hernia repair in relation to occupational mechanical exposures and a preventive potential of around 15% of all cases.