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.