Background

Repairs of primary ventral hernias are common procedures but are associated with high recurrence rates. Therefore, it is important to investigate risk factors for recurrence to optimize current treatments. The aim of this study was to assess the impact of annual surgeon volume on the risk of reoperation for recurrence after primary ventral hernia repair.

Study Design

We conducted a nationwide register-based study with data from the Danish Ventral Hernia Database and the Danish Patient Safety Authority’s Online Register linked via surgeons’ authorization identification. We included patients 18 years and older, undergoing umbilical or epigastric hernia repair between 2011 and 2020. Annual surgeon volume was categorized into ≤ 9, 10 to 19, 20 to 29, and ≥ 30 cases. Patients were followed until reoperation, death, emigration, or end of the study period.

Results

We included 7,868 patients who underwent laparoscopic (n = 1,529 [19%]), open mesh (n = 4,138 [53%]), or open nonmesh (n = 2,201 [28%]) repair. There was an increased risk of reoperation after laparoscopic umbilical or epigastric hernia repair for surgeons with ≤ 9 (hazard ratio 6.57; p = 0.008), 10 to 19 (hazard ratio 6.58; p = 0.011), and 20 to 29 (hazard ratio 13.59; p = 0.001) compared with ≥ 30 cases/y. There were no differences in risk of reoperation after open mesh and open nonmesh repair in relation to annual surgeon volume.

Conclusions

There was a significantly higher risk of reoperation after laparoscopic primary ventral hernia repair performed by lower-volume surgeons compared with high-volume surgeons. Additional research investigating how sufficient surgical training and supervision are ensured is indicated to reduce risk of reoperation after primary ventral hernia repair.

Visual AbstractIn primary ventral hernia repair, recurrence or reoperation rates are commonly used to assess long-term outcomes.1Henriksen N.A. Montgomery A. Kaufmann R. et al.Guidelines for treatment of umbilical and epigastric hernias from the European Hernia Society and Americas Hernia Society. Ventral hernia repair is a common surgical procedure,2Poulose B.K. Shelton J. Phillips S. et al.Epidemiology and cost of ventral hernia repair: making the case for hernia research. however, recurrences rates are still as high as 22%.3Christoffersen M.W. Brandt E. Helgstrand F. et al.Recurrence rate after absorbable tack fixation of mesh in laparoscopic incisional hernia repair. Reoperation rate underestimates the clinical recurrence rate, as only approximately 30% of clinical recurrences are reoperated.4Helgstrand F. Rosenberg J. Kehlet H. et al.Reoperation versus clinical recurrence rate after ventral hernia repair. One study found that the use of mesh halved the recurrence rate after small primary ventral hernia repairs compared with open nonmesh repairs.5Christoffersen M.W. Helgstrand F. Rosenberg J. et al.Long-term recurrence and chronic pain after repair for small umbilical or epigastric hernias: a regional cohort study. Other factors that can influence recurrence rates after umbilical and epigastric hernia repairs are hernia defect size,6Donovan K. Denham M. Kuchta K. et al.Predictors for recurrence after open umbilical hernia repair in 979 patients. surgical approach,7Hajibandeh S. Hajibandeh S. Sreh A. et al.Laparoscopic versus open umbilical or paraumbilical hernia repair: a systematic review and meta-analysis. use of mesh,8Bisgaard T. Kaufmann R. Christoffersen M. et al.Lower risk of recurrence after mesh repair versus non-mesh sutured repair in open umbilical hernia repair: a systematic review and meta-analysis of randomized controlled trials. mesh placement,9Holihan J.L. Nguyen D.H. Nguyen M.T. et al.Mesh location in open ventral hernia repair: a systematic review and network meta-analysis. and method of mesh fixation.10Baker J.J. Öberg S. Andresen K. et al.Systematic review and network meta-analysis of methods of mesh fixation during laparoscopic ventral hernia repair. Surgeons with more experience and high annual volume of procedures seemed to affect reoperation rates after inguinal hernia repair11Christophersen C. Fonnes S. Andresen K. et al.Lower recurrence rate after groin and primary ventral hernia repair performed by high-volume surgeons: a systematic review. and incisional hernia repair.12Aquina C.T. Kelly K.N. Probst C.P. et al.Surgeon volume plays a significant role in outcomes and cost following open incisional hernia repair. The effect of annual surgeon volume on reoperation rate after primary ventral hernia repair has only been reported in 1 previous study, which indicated an impact of annual surgeon volume on reoperation rates.13Aquina C.T. Fleming F.J. Becerra A.Z. et al.Explaining variation in ventral and inguinal hernia repair outcomes: a population-based analysis. However, this previous study did not provide data on hernia defect size, mesh placement, or fixation method, and the study cohort was based on diagnostic codes, which did not distinguish between primary and recurrent hernias.13Aquina C.T. Fleming F.J. Becerra A.Z. et al.Explaining variation in ventral and inguinal hernia repair outcomes: a population-based analysis. Therefore, there is a need to investigate how annual surgeon volume affects outcomes of ventral hernia repair, with more details about the operative technique.

The aim of this study was to assess how annual surgeon volume impacts the risk of reoperation for recurrence after umbilical and epigastric hernia repair.

MethodsThis nationwide register-based study with prospectively collected data followed the RECORD (Reporting of Studies Conducted Using Observational Routine-Collected Health Data) statement.14Benchimol E.I. Smeeth L. Guttmann A. et al.The REporting of studies Conducted using Observational Routinely-collected health Data (RECORD) statement. We used data from the Danish Ventral Hernia Database15Helgstrand F. Jorgensen L.N. The Danish ventral hernia database—a valuable tool for quality assessment and research. and Patient Safety Authority’s Online Register.16Danish Patient Safety Authority
Information about the online register. The Danish Ventral Hernia Database was established in 2007 and contains patient demographic and perioperative data, which are described elsewhere.17Rosenberg J. Friis-Andersen H. Jørgensen L. et al.Variables in the Danish hernia databases: inguinal and ventral. The Danish Ventral Hernia Database also draws data from the Danish National Patient Registry via patients’ unique personal identification (ID) number, providing data on all patient contacts with both public and private healthcare providers.18Schmidt M. Schmidt S.A.J. Sandegaard J.L. et al.The Danish National Patient Registry: a review of content, data quality, and research potential. In addition, the Danish Ventral Hernia Database is linked with data from the Danish Civil Registration System, via patients’ unique personal ID number,19The Danish Civil Registration System. making it possible to identify patients who emigrated or died during follow-up. The publicly available Danish Patient Safety Authority’s Online Register16Danish Patient Safety Authority
Information about the online register. provides data on surgeons’ authorization ID, authorization status, surgeon’s date of birth, date of authorization, field of specialization, and date of approved specialization. In this study, patient data from the Danish Ventral Hernia Database were linked with data on surgeons from the Danish Patient Safety Authority’s Online Register via surgeons’ unique authorization ID.

The study period was January 2011 to January 2020 and registration of surgeon authorization ID became mandatory in the Danish Ventral Hernia Database from 2016 and onward for all repairs. Patients were followed via the database until death, reoperation, emigration, or the end of the study period (January 2020). We defined reoperation as hernias registered as a reoperation or an operation for a ventral hernia after the index operation.

All patients registered in the Danish Ventral Hernia Database were assessed for eligibility. We included patients 18 years and older undergoing primary umbilical or epigastric hernia repair and undergoing either laparoscopic or open technique. Surgeons were included if they had a valid authorization ID registered. Patients were excluded if they were younger than 18 years and if the first registered operation was for recurrence. In addition, we performed a “look back” from 2007 to 2011, and patients who underwent operation for a ventral hernia previously were excluded. Patients were excluded if the index operation was an incisional or parastomal hernia, or if patients underwent operations for both umbilical and epigastric hernias on the same day. Patients were also excluded if they underwent procedures using robot-assisted techniques, were converted from laparoscopic to open technique, had a hernia defect size > 10 cm in transverse diameter, or had undergone repairs performed using resorbable mesh types or Physiomesh (because this mesh was withdrawn due to high risk of reoperation).20US Food and Drug Administration
Ethicon voluntarily withdraws Physiomesh. In addition, exclusion criteria were use of component separation, repairs performed as secondary procedures, open repairs with inlay mesh, patient residence outside of Denmark, or invalid surgeon authorization ID.The primary end point was risk of reoperation or recurrence based on annual surgeon volume. The secondary outcomes were how risk of reoperation was affected by surgeon’s age, which was dichotomized into younger than 45 years and 45 years and older,21Neumayer L.A. Gawande A.A. Wang J. et al.Proficiency of surgeons in inguinal hernia repair: effect of experience and age. and years since surgeon’s graduation and specialization. Surgeon’s annual volume was divided into 4 categories based on annual volume: 1 low-volume category (≤ 9), 2 intermediate-volume categories (10 to 19 and 20 to 29), and 1 high-volume category (≥ 30). This categorization was based on a previous study investigating annual surgeon volume and outcomes of ventral hernia repair.13Aquina C.T. Fleming F.J. Becerra A.Z. et al.Explaining variation in ventral and inguinal hernia repair outcomes: a population-based analysis. The annual surgeon volume was calculated as the number of repairs performed during the year before the index repair. This allowed annual surgeon volume to be a dynamic variable, making it possible for surgeons to change volume category. During the first year of the study period, the number of repairs from the current calendar year was used to calculate the annual surgeon volume for each surgeon because surgeons’ authorization IDs for the previous year were not available. The data on surgeons were presented for the volume category in which the individual surgeon performed most of their repairs.Patients were divided into the following 3 cohorts: laparoscopic, open mesh, and open nonmesh. We performed a subgroup analysis dichotomizing hernia defect size into ≤ 2 cm and > 2 cm.22Muysoms F.E. Miserez M. Berrevoet F. et al.Classification of primary and incisional abdominal wall hernias. In addition, sensitivity analyses were conducted that investigated how the calculation of annual surgeon volume impacted outcomes.The statistical analyses were carried out in SPSS, version 25.0 (IBM Corp). The distribution of continuous data was assessed visually with Q-Q plots and histograms. Normally distributed data were presented as mean ± SD. Not normally distributed data were presented as median (interquartile range [IQR]). Continuous data were analyzed using the nonparametric Kruskal-Wallis and Dunn's tests. Categorical data were analyzed using the independent chi-square test, with surgeons performing ≥ 30 repairs annually as the reference group. A p value ≤ 0.05 was assessed as significant. We performed multivariate analyses using the Cox proportional hazard analysis, presented as hazard ratio (HR) with 95% CI. In Cox proportional hazard analysis, a rule of thumb is to adjust for 1 variable per approximately 10 events.23Peduzzi P. Concato J. Kemper E. et al.A simulation study of the number of events per variable in logistic regression analysis. Through backward stepwise elimination, with p = 0.2 as the cutoff, we chose to adjust for anatomic mesh placement, type of tacks, and emergency vs elective repair in the laparoscopic cohort. In the open mesh cohort, the multivariate analysis was adjusted for anatomic mesh placement; emergency vs elective repair; hernia defect size; and patient’s sex, age, BMI, and smoking status. In the open nonmesh cohort, the multivariate analysis was adjusted for emergency vs elective repair; hernia defect size; and patient’s sex, age, BMI, and smoking status. Surgeons performing ≥ 30 cases/y were used as the reference group in the multivariate analyses. Kaplan-Meier plots were used to illustrate the cumulative reoperation rates.

This study was approved by the Danish Clinical Quality Program (RKKP) and the Danish Data Protection Agency (P-2020-380). According to Danish law, approval from ethics committees and informed written consent from participants were not required.

ResultsWe included 7,868 patients undergoing primary umbilical or epigastric hernia repair by means of laparoscopic (n = 1,529 [19%]), open mesh (n = 4,138 [53%]), or open nonmesh (n = 2,201 [28%]) repair. A flow chart of the study population selection is shown in Figure 1. The patient and operative characteristics are shown in Table 1 for the laparoscopic cohort, in Table 2 for the open mesh cohort, and in Table 3 for the open nonmesh repair cohort. The high-volume category surgeons performing ≥ 30 cases/y repaired small (≤ 2 cm) hernias more frequently than hernias > 2 cm in the laparoscopic (64%), open mesh (91%), and open nonmesh (100%) cohorts. These high-volume surgeons performed few emergency repairs in the laparoscopic (2%), open mesh (2%), and open nonmesh cohorts (0%). In all 3 cohorts, the low- and intermediate-volume category surgeons performed most of the emergency repairs. The median follow-up for the laparoscopic, open mesh, and open nonmesh cohorts were 23 (IQR 13 to 33) months, 19 (IQR 9 to 31) months, and 26 (IQR 13 to 35) months, respectively. We included 725 surgeons and the characteristics of included surgeons are shown in Table 4.

Figure 1Flow chart depicting the study population selection.

Table 1Patient and Operative Characteristics for the Laparoscopic Cohort

The ≥ 30 cases annual volume category was used as the reference in the independent chi-square, Kruskal-Wallis, and Dunn's tests.

IQR, interquartile range.

Table 2Patient and Operative Characteristics for the Open Mesh Cohort

The ≥ 30 volume category was used as the reference in the independent chi-square, Kruskal-Wallis, and Dunn's tests.

IQR, interquartile range.

Table 3Patient and Operative Characteristics for the Open Nonmesh Cohort

The ≥ 30 volume category was used as the reference in the independent chi-square, Kruskal-Wallis, and Dunn's tests.

IQR, interquartile range.

Table 4Characteristics of Included Surgeons∗

Surgeon data are presented for the volume category in which the individual surgeon performed repairs most frequently.

IQR, interquartile range.

The risk of reoperation after laparoscopic umbilical and epigastric repairs was significantly increased when performed by surgeons with an annual volume of ≤ 9 (HR 6.57; p = 0.008), 10 to 19 (HR 6.58; p = 0.011), and 20 to 29 (HR 12.59; p = 0.001) compared with ≥ 30 cases (Table 5). The Cox proportional hazard analysis was adjusted for anatomic mesh placement, type of tacks, and emergency vs elective repair, and is presented in eTable 1. The cumulative reoperation rates for the surgeon volume categories are shown in Figure 2A . High-volume surgeons placed the mesh preperitoneally (64%) (p Table 5Risk of Reoperation Based on Annual Surgeon Volume Assessed with Cox Proportional Hazard Analyses∗

The number of variables adjusted for in the analyses depended on the number of events in the respective cohorts.

Figure 2Kaplan-Meier plots showing the (A) cumulative reoperation rate after laparoscopic repair of primary ventral hernia reported based on annual surgeon volume (p = 0.070) and the number of patients. (B) Cumulative reoperation rate after open mesh repair of primary ventral hernia reported based on annual surgeon volume (p = 0.047) and number of patients.(C) Cumulative reoperation rate after open nonmesh repair of primary ventral hernia reported based on annual surgeon volume (p = 0.792) and number of patients.

Figure 2Kaplan-Meier plots showing the (A) cumulative reoperation rate after laparoscopic repair of primary ventral hernia reported based on annual surgeon volume (p = 0.070) and the number of patients. (B) Cumulative reoperation rate after open mesh repair of primary ventral hernia reported based on annual surgeon volume (p = 0.047) and number of patients.(C) Cumulative reoperation rate after open nonmesh repair of primary ventral hernia reported based on annual surgeon volume (p = 0.792) and number of patients.

Annual surgeon volume did not impact the risk of reoperation after open mesh umbilical or epigastric repairs compared with high-volume surgeons, as is shown in Table 5. Annual volume of ≤ 9 and 10 to 19 cases seemed to have a lower risk of reoperation, and 20 to 29 cases seemed to have a higher risk of reoperation after open mesh umbilical or epigastric hernia repair compared with ≥ 30 cases. The Cox proportional hazard analysis was adjusted for mesh placement, emergency vs elective repair, hernia defect size, patient’s sex, age, BMI, and smoking status, and is shown in eTable 1. The cumulative reoperation rates separated for the annual surgeon volume categories are shown in Figure 2B. The majority of open mesh repairs were performed by surgeons in the ≤ 9 (60%) and 10 to 19 (20%) cases/y categories. Surgeons in the low- and intermediate-volume categories of ≤ 9 (69%), 10 to 19 (66%), and 20 to 29 (39%) placed the mesh as onlay more frequently compared with those in the ≥ 30 cases/y category (22%) (p Annual surgeon volume did not impact the risk of reoperation compared with high-volume surgeons for open nonmesh repair (Table 5). The Cox proportional hazard analysis was adjusted for emergency vs elective repair, hernia defect size, patients’ sex, age, BMI, and smoking status, as shown in eTable 1. The cumulative reoperation rates for each annual surgeon volume category are shown in Figure 2C. Most of the repairs in this cohort were performed by surgeons with ≤ 9 (72%) and 10 to 19 (20%) cases/y.

In addition, analyses were conducted to investigate secondary outcomes. Firstly, we investigated how surgeon’s age dichotomized into younger than 45 years and 45 years and older affected the crude reoperation rate. In the open mesh cohort, there was a significant difference in the reoperation rates for surgeons younger than 45 years (1.5%) and 45 years and older (2.8%) (p = 0.006). In the laparoscopic (p = 0.387) and open nonmesh (p = 0.683) cohorts, there were no significant differences in the crude reoperation rates between surgeons younger than 45 years and 45 years and older. Secondly, we analyzed how the number of years since surgeon’s graduation affected the risk of reoperation. The number of years since surgeon’s graduation was associated with significantly increased risk of reoperation after open mesh repair. Thirdly, we investigated how the number of years since surgeon’s specialization affected the risk of reoperation after umbilical or epigastric hernia repair. The number of years since surgeon’s specialization did not impact the risk of reoperation.

Subgroup analyses were performed for hernia defect size ≤ 2 cm and > 2 cm. We found an increased risk of reoperation based on annual surgeon volume after laparoscopic repair of umbilical and epigastric hernias of ≤ 2 cm (eTable 2).

Lastly, sensitivity analyses were conducted from which repairs performed during the first year of the individual surgeon’s operating career were excluded. In the laparoscopic cohort, the sensitivity analyses showed a similar increased risk of reoperation for all categories of lower-volume surgeons compared with high-volume surgeons, but results were only significant for the 20 to 29 cases/y volume category (HR 7.86; p = 0.012). For the open mesh and open nonmesh cohorts, the tendencies were similar to the primary analyses of risk of reoperation across the annual volume categories (analyses not shown).

Discussion

In this nationwide register-based study, we found that annual surgeon volume of < 30 cases was associated with a higher risk of reoperation after laparoscopic repair of umbilical and epigastric hernias compared with high-volume surgeons of ≥ 30 cases. Annual surgeon volume did not seem to impact the risk of reoperation after open mesh and open nonmesh repair of umbilical and epigastric hernias.

To our knowledge, only 1 previous study reported annual surgeon volume and risk of reoperation after primary ventral hernia repairs. In that study, the authors found a decreased risk of reoperation for both laparoscopic and open primary ventral hernia repairs performed by high-volume surgeons of ≥ 30 cases/y compared with low-volume surgeons of ≤ 9 cases/y.13Aquina C.T. Fleming F.J. Becerra A.Z. et al.Explaining variation in ventral and inguinal hernia repair outcomes: a population-based analysis. However, they did not adjust for the different anatomic mesh placements in their analyses, making it difficult to directly compare their findings with our study population. Interestingly, in the open mesh cohort, we found that high-volume surgeons primarily placed the mesh preperitoneally and low-volume surgeons placed the mesh as onlay. Preperitoneal mesh placement is a more complex procedure because it requires dissection of the preperitoneal space,24Abdominal wall spaces for mesh placement: onlay, sublay, underlay. and this might explain why high-volume surgeons performed most of these repairs. According to current guidelines, the mesh should be placed preperitoneal in open repair when feasible, as it reduces the risk of reoperation and complications compared with other mesh placements1Henriksen N.A. Montgomery A. Kaufmann R. et al.Guidelines for treatment of umbilical and epigastric hernias from the European Hernia Society and Americas Hernia Society.; however, the strength of recommendation in the guideline was graded as weak. Therefore, it is important to ensure adequate training and education, enabling younger surgeons and surgeons with lower annual volume to perform preperitoneal mesh placement. In addition, we found that most of the laparoscopic preperitoneal mesh repairs were performed by high-volume surgeons, and lower-volume surgeons in the laparoscopic cohort placed the mesh intraperitoneally. In the laparoscopic cohort, high-volume surgeons primarily used permanent tacks, and intermediate-volume surgeons used absorbable tacks more frequently. Absorbable tacks are associated with an increased risk of reoperation3Christoffersen M.W. Brandt E. Helgstrand F. et al.Recurrence rate after absorbable tack fixation of mesh in laparoscopic incisional hernia repair.,10Baker J.J. Öberg S. Andresen K. et al.Systematic review and network meta-analysis of methods of mesh fixation during laparoscopic ventral hernia repair. and use of permanent tacks is recommended.1Henriksen N.A. Montgomery A. Kaufmann R. et al.Guidelines for treatment of umbilical and epigastric hernias from the European Hernia Society and Americas Hernia Society. The increased risk of reoperation after laparoscopic umbilical or epigastric hernia repair performed by lower-volume surgeons compared with high-volume surgeons could perhaps be explained by insufficient training and supervision of lower-volume surgeons in our laparoscopic cohort. However, surgical training and supervision is outside the scope of the current study, and additional research is needed to investigate how sufficient surgical training and supervision are ensured. In the open mesh and open nonmesh repair cohorts, the high-volume surgeons performed few of the repairs. The majority of repairs in these cohorts were performed by surgeons in the lower-volume categories. It is important to ensure adequate supervision of lower-volume surgeons performing umbilical and epigastric hernia repair.There are several strengths to this nationwide register-based study. The Danish Ventral Hernia Database has nationwide coverage and includes both public and private hospitals and approximately 80% of ventral hernia repairs performed in Denmark are registered in the database,15Helgstrand F. Jorgensen L.N. The Danish ventral hernia database—a valuable tool for quality assessment and research. reducing the risk of selection bias of included patients. In addition, the follow-up on patients in the Danish Ventral Hernia Database is close to 100%15Helgstrand F. Jorgensen L.N. The Danish ventral hernia database—a valuable tool for quality assessment and research. because the database holds data from the Danish National Patient Registry18Schmidt M. Schmidt S.A.J. Sandegaard J.L. et al.The Danish National Patient Registry: a review of content, data quality, and research potential. and the Danish Civil Registration System.19The Danish Civil Registration System. Another strength of this study was that we only included primary ventral hernia repairs because differences between primary ventral and incisional hernias have been reported for both surgical management and outcomes.25Köckerling F. Schug-Paß C. Adolf D. et al.Is pooled data analysis of ventral and incisional hernia repair acceptable?. In addition, this study used the specific annual surgeon volume and not hospital volume as an indirect measure of surgeon’s annual volume, and the annual surgeon volume categories were defined according to pre-existing literature.13Aquina C.T. Fleming F.J. Becerra A.Z. et al.Explaining variation in ventral and inguinal hernia repair outcomes: a population-based analysis. The annual surgeon volume was calculated as a dynamic variable that allowed surgeons to change volume categories during the study period, reflecting the varying nature of the number of repairs the individual surgeon performs throughout a 4-year period. The variables adjusted for in the Cox proportional hazard analyses were chosen through backward stepwise elimination, ensuring that the multivariate analyses were adjusted for the relevant covariates, and the multivariate analyses were adjusted for operative characteristics known to affect the risk of reoperation. Yet, the study size was limited by the data availability of surgeons’ authorization IDs in the Danish Ventral Hernia Database, which was mandatory from 2016 and onward. Data on patients’ BMI and smoking status were only available for 68% of the included patients. The Danish Ventral Hernia Database includes few robot-assisted hernia repairs because this technique is not used frequently in Denmark, therefore, it was not possible to investigate the impact of annual surgeon volume on robot-assisted ventral hernia repair outcomes in this study population. The impact of annual surgeon volume on outcomes after robot-assisted ventral hernia repair should be investigated in a population in which the technique is used more frequently. Another limitation to this study was that we used reoperation rate as a measure for recurrence rate. A previous study found that reoperation rate underestimates the clinical recurrence rate, as only approximately 30% of clinical recurrences are reoperated.4Helgstrand F. Rosenberg J. Kehlet H. et al.Reoperation versus clinical recurrence rate after ventral hernia repair. Lastly, there was a risk of a statistical type 2 error in the analyses of the cohorts for open mesh and nonmesh, and it is therefore possible that our findings would reach statistical significance in a larger sample size.Conclusions

We found a higher risk of reoperation after laparoscopic umbilical and epigastric hernia repairs performed by low- and intermediate-volume surgeons compared with high-volume surgeons. This might raise a discussion of centralization of laparoscopic umbilical and epigastric hernia repairs on fewer surgeons with high annual volumes to ensure better long-term outcomes for patients. However, factors such as surgical training and geography can impact the feasibility of centralizing laparoscopic umbilical and epigastric hernia repair. We found no significant impact of annual surgeon volume on risk of reoperation after open mesh and open nonmesh repair of umbilical and epigastric repairs.

 Author Contributions

Study conception and design: Christophersen, Fonnes, Andresen, Rosenberg

Acquisition of data: Andresen

Analysis and interpretation of data: Christophersen, Baker, Andresen

Drafting of manuscript: Christophersen

Critical revision: Christophersen, Fonnes, Baker, Andresen, Rosenberg

Acknowledgment

The authors thank Lasse Valentini Jensen for assistance with the acquisition of data.

Appendix