BACKGROUND: The repair of inguinal hernias is a common surgical procedure. Some patients will need a second operation after developing a metachronous contralateral inguinal hernia (MCIH). The suggestion has been made to strengthen the contralateral side at the same time as primary unilateral surgery. In this systematic review we aim to determine how many adult patients with a unilateral inguinal hernia will develop a MCIH.
METHODS: This review was reported in line with PRISMA guidelines. We performed a literature review in PubMed Publisher, Embase, Google Scholar and Cochrane Library until May 2021, including articles reporting MCIH after unilateral inguinal hernia repair in adults. As outcome measure, the number of patients diagnosed with a MCIH was registered.
RESULTS: A total of 19 articles with a total of 277,288 patients were included. The combined estimate for MCIH after meta-analysis equaled 8.3% (95% CI 7.1%-9.5%), with a high index of heterogeneity (I2 = 97.9%). A random-effects meta-regression was performed to obtain the percentage of MCIH as a function of median follow-up time. The percentage of MCIH at 3, 5 and 10 years was estimated at 5.2%, 8.0% and 17.1%, respectively.
CONCLUSIONS: We suggest that there is insufficient clinical evidence to support prophylactic contralateral repair in all patients. We propose a patient-specific approach in the decision to perform prophylactic repair, taking into account potential risk factors for hernia development, type of surgical approach, and general risk factors for chronic postoperative inguinal pain. More long-term prospective data are needed to guide the decision for prophylactic contralateral mesh placement.

BACKGROUND: Patients undergoing unilateral inguinal hernia repair (IHR) are at risk of metachronous contralateral inguinal hernia (MCIH) development. We evaluated incidence and risk factors of MCIH development up to 25 years after unilateral IHR to determine possible indications for concomitant prophylactic surgery of the contralateral groin at the time of primary surgery.
METHODS: Patients between 18 and 70 years of age undergoing elective unilateral IHR in the University Hospital of Leuven from 1995 to 1999 were studied retrospectively using the electronic health records and prospectively via phone calls. Study aims were MCIH incidence and risk factor determination. Kaplan-Meier curves were constructed and univariable and multivariable Cox regressions were performed.
RESULTS: 758 patients were included (91% male, median age 53 years). Median follow-up time was 21.75 years. The incidence of operated MCIH after 5 years was 5.6%, after 15 years 16.1%, and after 25 years 24.7%. The incidence of both operated and non-operated MCIH after 5 years was 5.9%, after 15 years 16.7%, and after 25 years 29.0%. MCIH risk increased with older age and decreased in primary right-sided IHR and higher BMI at primary surgery.
CONCLUSIONS: The overall incidence of MCIH after 25-year follow-up is 29.0%. Potential risk factors for the development of a MCIH are primary left-sided inguinal hernia repair, lower BMI, and older age. When considering prophylactic repair, we suggest a patient-specific approach taking into account these risk factors, the surgical approach and the risk factors for chronic postoperative inguinal pain.

BACKGROUND: Following repair of a unilateral inguinal hernia, there is a risk of 1% per year of onset of an inguinal hernia on the other side. Comparison of bilateral with unilateral TAPP operation in a high-volume center found that morbidity and reoperation rates were only marginally higher for bilateral TAPP operation. Some authors are calling for prophylactic operation of the contralateral side.
METHODS: Between September 2009 and April 2013, data were entered into the Herniamed Registry on 15,176 patients who had undergone TAPP operation. Of these patients, 10,887 had been operated on because of a unilateral (71.7%) and 4289 because of a bilateral (28.3%) inguinal hernia.
RESULTS: A significant difference was noted in the rate of postoperative complications occurring within 30 days, which was 4.9% for bilateral compared with 3.9% for unilateral inguinal hernia (p = 0.009). The postoperative complications necessitated reoperation in 0.9% of patients after unilateral and in 1.9% of patients after bilateral inguinal hernia repair, thus attesting to the significantly higher risk presented by bilateral inguinal hernia repair (p = <0.001).Multivariate analysis confirmed the highly significant influence of bilateral TAPP on increased reoperation rates due to complications (p > 0.0001). The odds ratio was 2.13 (95% CI 1.58-2.86). Comparison of the results from a high-volume center with those from the Herniamed Registry showed that perioperative complication rates were markedly higher.
CONCLUSIONS: Perioperative outcome of bilateral TAPP operation demonstrates significantly worse postoperative complication and reoperation rates compared with unilateral TAPP. Likewise, the results were markedly unfavorable compared with those of a high-volume center. If a bilateral hernia repair should be attempted in those patients with only a unilateral hernia, these data give the surgeon more information on how to better prepare a patient and obtain consent preoperatively.