Abstract: We included 25 studies (6293 participants) in this review. All included studies specified inguinal hernias, and two studies reported that femoral hernias were included. Mesh repair probably reduces the risk of hernia recurrence compared to non-mesh repair (21 studies, 5575 participants; RR 0.46, 95% CI 0.26 to 0.80, I2 = 44%, moderate-quality evidence). In absolute numbers, one hernia recurrence was prevented for every 46 mesh repairs compared with non-mesh repairs. Twenty-four studies (6293 participants) assessed a wide range of complications with varying follow-up times. Neurovascular and visceral injuries were more common in non-mesh repair groups (RR 0.61, 95% CI 0.49 to 0.76, I2 = 0%, NNTB = 22, high-quality evidence). Wound infection was found slightly more commonly in the mesh group (20 studies, 4540 participants; RR 1.29, 95% CI 0.89 to 1.86, I2 = 0%, NNTB = 200, low-quality evidence). Mesh repair reduced the risk of haematoma compared to non-mesh repair (15 studies, 3773 participants; RR 0.88, 95% CI 0.68 to 1.13, I2 = 0%, NNTB = 143, low-quality evidence). Seromas probably occur more frequently with mesh repair than with non-mesh repair (14 studies, 2640 participants; RR 1.63, 95% CI 1.03 to 2.59, I2 = 0%, NNTB = 72, moderate-quality evidence), as does wound swelling (two studies, 388 participants; RR 4.56, 95% CI 1.02 to 20.48, I2 = 33%, NNTB = 72, moderate-quality evidence). The comparative effect on wound dehiscence is uncertain due to wide confidence intervals (two studies, 329 participants; RR 0.55, 95% CI 0.12 to 2.48, I2 = 37% NNTB = 77, low-quality evidence). Testicular complications showed nearly equivocal results; they probably occurred slightly more often in the mesh group however the confidence interval around the effect was wide (14 studies, 3741 participants; RR 1.06, 95% CI 0.63 to 1.76, I2 = 0%, NNTB = 2000, low-quality evidence). Mesh reduced the risk of postoperative urinary retention compared to non-mesh (eight studies, 1539 participants; RR 0.53, 95% CI 0.38 to 0.73, I2 = 56%, NNTB = 16, moderate-quality evidence). Postoperative and chronic pain could not be compared due to variations in measurement methods and follow-up time (low-quality evidence). No deaths occurred during the follow-up periods reported in the seven studies (2546 participants) reporting this outcome (high-quality evidence). The average operating time was longer for non-mesh repairs by a mean of 4 minutes 22 seconds, despite wide variation across the studies regarding size and direction of effect, thus this result is uncertain (20 studies, 4148 participants; 95% CI -6.85 to -1.60, I2= 97%, very low-quality evidence). Hospital stay may be shorter with mesh repair, by 0.6 days (12 studies, 2966 participants; 95% CI -0.86 to -0.34, I2 = 98%, low-quality evidence), and participants undergoing mesh repairs may return to normal activities of daily living a mean of 2.87 days sooner than those with non-mesh repair (10 studies, 3183 participants; 95% CI -4.42 to -1.32, I2 = 96%, low-quality evidence), although the results of both these outcomes are also limited by wide variation in the size and direction of effect across the studies. Mesh and non-mesh repairs are effective surgical approaches in treating hernias, each demonstrating benefits in different areas. Compared to non-mesh repairs, mesh repairs probably reduce the rate of hernia recurrence, and reduce visceral or neurovascular injuries, making mesh repair a common repair approach. Mesh repairs may result in a reduced length of hospital stay and time to return to activities of daily living, but these results are uncertain due to variation in the results of the studies. Non-mesh repair is less likely to cause seroma formation and has been favoured in low-income countries due to low cost and reduced availability of mesh materials. Risk of bias in the included studies was low to moderate and generally handled well by study authors, with attention to details of allocation, blinding, attrition and reporting.

Plain-language summary: In this update of a review originally published in 2001, we included a total of 25 studies (with a total of 6293 people) undertaken in a number of different countries. A variety of outcomes were assessed, including return of the hernia after initial repair (hernia recurrence), a variety of complications including pain, duration of surgery, hospital stay and time before going back to normal activities. One hernia recurrence is prevented for every 46 mesh repairs performed rather than non-mesh repairs. Compared to non-mesh repairs, mesh repairs are more likely to develop collections of fluid next to the surgical wound, but are less likely to result in difficulty urinating following the operation, or injury to nerves, blood vessels or other organs. Postoperative pain could not be clearly compared between studies due to differences in measurement methods and time frames, but overall the studies appeared to indicate that participants who had mesh repairs had less pain. The length of the surgical operation was slightly shorter for mesh repairs. Participants who had a mesh repair were more likely to have a shorter hospital stay and had a shorter average recovery time before returning to their normal activities. The studies included in this review used good-quality methods, considered potential factors which could affect the results, and addressed their proposed outcomes clearly. In our assessment of the quality of evidence, we marked down some outcomes to 'moderate' quality, particularly due to variability within results. Overall, hernia repairs with and without mesh both proved effective in the treatment of hernias, although mesh repairs demonstrated fewer hernia recurrences, a shorter operation time and faster return to normal activities. Non-mesh repairs are still widely used, often due to the cost and poor availability of the mesh product itself.