Risk and prognosis of inguinal hernia in relation to occupational mechanical exposures--a systematic review of the epidemiologic evidence.

OBJECTIVES The aim of this review was to evaluate the epidemiologic evidence for (i) a causal effect of occupational mechanical exposures on incidence of inguinal hernia, and (ii) a prognostic effect of such exposures on hernia recurrence and persistent pain after inguinal hernia repair. METHODS We performed a literature search in Medline, Embase, and Web of Science up to 3 November 2011. Central information was extracted from included studies, and strengths and limitations were discussed. RESULTS All 23 included studies focused on effects of (work) activities that hardly reflected specific occupational risk factors. Eight studies provided information on risk by occupation or occupational activities. Increased risk was reported in six studies, but inflationary bias was likely. The negative findings in two studies might well be explained by bias towards the null due to crude exposure and/or outcome assessment. Three studies on single strenuous events primarily reflected patients` beliefs regarding risk factors. Information on prognosis with respect to recurrence was found in seven studies. The studies used crude exposure assessment, and two were also underpowered. Four suggested an increased risk. Six studies on prognosis with respect to persistent pain (one of which also concerned recurrence) were practically non-informative for the purpose of this review. CONCLUSIONS There is insufficient epidemiologic evidence to draw meaningful conclusions about (i) the existence of causal associations between specific occupational mechanical exposures and the development of inguinal hernia, and (ii) the influence of these exposures on prognosis after inguinal hernia repair with respect to hernia recurrence and persistent pain.