At least ninety days of follow-up are required to adequately detect wound outcomes after open incisional hernia repair.
Background: Incisional hernia repair (IHR) carries a high risk of wound complications. Thirty-day outcomes are frequently used in comparative-effectiveness research, but may miss a substantial number of surgical site occurrences (SSO) including surgical site infection (SSI). The objective of this study was to determine an optimal length of follow-up to detect SSI after IHR.
Methods: All adult patients undergoing open IHR at a single academic center over a 3 year period were reviewed. SSIs, non-infectious SSOs, and wound-related readmissions were recorded up to 180 days. The primary outcome was the proportion of SSIs detected at end-points of 30, 60, and 90 days of follow-up. Time-to-event analysis was performed for all outcomes at 30, 60, 90, and 180 days. Logistic regression was used estimate the relative risk of SSI for relevant risk factors.
Results: A total of 234 patients underwent open IHR. Median follow-up time of 102 days. Overall incidence of SSI was 15.8% with median time to occurrence of 23 days. Incidence of non-infectious SSO was 33.2%, and SSO-related readmission was 12.8%. At 30, 60, and 90 days sensitivity was 81.6%, 89.5%, and 92.1 for SSI, and 46.7%, 76.7%, and 83.3% for readmission. In regression analysis, body mass index (RR 1.08, 95% CI 1.00, 1.15, p = 0.04) anterior component separation (RR 4.21, 95% CI 2.09, 6.34, p = 0.003), and emergency surgery (RR 3.25, 95% CI 1.47, 5.02, p = 0.01), were independently associated with SSI after adjusting for age, sex, contamination class, and procedure duration.
Conclusions: A considerable proportion of SSIs occurred beyond 30 days, but 90-day follow-up detected 92% of SSIs. Follow-up to 90 days captured only 83% of SSO-related readmissions. These results have implications for the design of trials evaluating wound complication after open IHR, as early endpoints may miss clinically relevant outcomes and underestimate the number needed to treat. Where possible, we recommend a minimum follow-up of 90 days to estimate wound complications following open IHR.