Long-term results of laparoscopic versus open intraperitoneal onlay mesh incisional hernia repair: a propensity score-matched analysis

Background Intraperitoneal onlay mesh repair (IPOM) of incisional hernia is performed by laparoscopic and open access. The aim of the present study is to compare open versus laparoscopic surgery specifically using an IPOM technique for incisional hernia repair. Methods A propensity score-matched observational single center study of patients that underwent IPOM between 2004 and 2015 was conducted. The primary outcome was hernia recurrence; secondary outcomes include length of stay, surgical site infections (SSI), complications, and localization of recurrence. Results Among 553 patients with incisional hernia repair, 59% underwent laparoscopic and 41% open IPOM. A total of 184 patients completed follow-up. After a mean follow-up of 5.5 years recurrence rate was 20% in laparoscopic and 19% in open repair (p = 1.000). Patients undergoing laparoscopic IPOM had significantly reduced operation time (median 120 vs. 180 min, p < 0.001), shorter hospital stays (6 vs. 8 days, p = 0.002), less complications (10 vs. 23%, p = 0.046), and fewer SSI (1 vs. 21%, p < 0.001). Conclusions Laparoscopic IPOM is associated with reduced morbidity compared to open IPOM for incisional hernia repair.

Incisional hernia is a frequent clinical challenge with an incidence between 11 and 23% after open abdominal surgery and is associated with relevant morbidity [1][2][3][4]. Trials and systematic reviews comparing laparoscopic with open surgical techniques showed reduced complications [5][6][7], less surgical site infections (SSI) [8][9][10], and a shorter hospital stay [5,8,9,11] in patients undergoing laparoscopic incisional hernia repair. These studies, however, are confounded by the fact that not just the route of access but also the type of surgery is different. In open incisional hernia surgery, meshes are most frequently positioned in sublay or preperitoneal position, while in laparoscopic hernia surgery the most frequent operation is an intraperitoneal onlay mesh (IPOM) [12][13][14]. To avoid mesh position as confounding factor, the present study focuses solely on hernias repaired by an IPOM technique, by either laparoscopic or open access.
The objective of the present study is to describe long-term results of hernia recurrence after laparoscopic versus open IPOM incisional hernia repair and to compare anatomical details of hernia recurrence between these two techniques.

Materials and methods
This retrospective cohort study is reported in accordance with the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) statement [15]. Inclusion criteria were incisional hernia repair in our institution between September 2004 and September 2015 and age above 18 years. Exclusion criteria were loss to follow-up, missing written consent or different operation technique than IPOM repair. Four patients were excluded because of mesh implantation in a sublay position. All patients eligible for inclusion were invited for clinical assessment in our outpatient department. If patients neither responded to phone calls nor to written convocation, contact was sought through the corresponding family doctor. Those patients not being able to attend clinical examination were interviewed by a standardized telephone questionnaire. All patients were examined and interviewed by the same independent investigator (SEB).
The primary outcome parameter was the incidence of hernia recurrence. Hernia recurrence was defined as proposed by Korenkov et al. [16]: "Any abdominal wall gap with or without bulge in the area of postoperative scar perceptible or palpable by clinical examinations or imaging." Ultrasonography was used if clinical examination was not unequivocal.
Secondary outcome variables were operation time, length of hospital stay, frequency of SSI as defined by the Centers of disease Control and Prevention (CDC) [17], complications as defined by Dindo et al. [18], reoperation, chronic pain, and localization of hernia relapse as defined by the European Hernia Society (EHS) [19]. Chronic pain was defined as pain of 4 or more out of 10 points on a visual analogue scale for 3 months or longer at the time of investigation according to the International Association for the Study of Pain [20].
Patient-related factors such as age, sex, body mass index (BMI), hernia size, length of hospital stay, and operation related factors such as mesh size and operation time were extracted from the medical records. The study design was approved by the cantonal ethics committee of Bern, Switzerland (KEK 152/15), and informed consent was obtained from all patients.

Statistical analysis
A 2:1 propensity score matching of the laparoscopic and the open IPOM group was performed. Matching criteria were age, sex, and BMI. Normality of distribution was assessed using the Shapiro-Wilk test. Categorical data were compared using Fisher's exact test and continuous data using Mann-Whitney U test for non-parametric distribution and two-sample t test for parametric distribution. Recurrence rates were shown as Kaplan-Meier curve and compared by Log rank testing. A significance level of < 0.05 was assumed to be statistical significant. Statistical analysis was performed using SPSS Statistics version 25 (IBM Corporation, Armonk, United States).

Results
Among 553

Recurrence rates
Overall recurrence rate was 20% (n = 19) in the laparoscopic group and 19% (n = 9) in the open group (p = 1.00) after a mean follow-up of 5.5 ± 3.0 years (Fig. 2). Recurrence rate was significantly increased in patients with SSI (log rank p = 0.002) and BMI ≥ 30 kg/m 2 (log rank p = 0.013) but not dependent on mesh size or type of fixation ( Fig. 3A-D).

Secondary outcomes
Median operation time (120 vs. 180 min, p < 0.001) and median length of hospital stay (6 vs. 8 days, p = 0.002) were significantly shorter after laparoscopic incisional hernia repair. Complications (10 vs. 23%, p = 0.046) and SSI (1 vs. 21%, p < 0.001) were significantly fewer in laparoscopic compared to open repair ( Table 2). There were no significant differences in mesh size, frequency of reoperation chronic pain, and overall complications between the two groups.

Localization of recurrence
Hernia recurrence in patients with median laparotomy as initial surgical access was mainly seen in the epigastric region (EHS classification M2) regardless if hernia repair was performed open or laparoscopically (Fig. 4A, C). In patients  after oblique laparotomy as initial incision, recurrence after laparoscopic hernia repair was mainly seen in the epigastric region (EHS classification M2), whereas after open incisional hernia repair, hernia recurrence was mainly seen in the flank (EHS classification L2) (Fig. 4B, D).

Discussion
To our knowledge, this is the first report that compares longterm results of laparoscopic versus open IPOM. The present study reveals the typical advantages of laparoscopic hernia repair: Shorter hospital stay and reduced SSI. Thus, avoiding mesh position as confounder, by including only IPOM in both arms, the present study supports the finding that primarily the access route provides these advantages [5-9, 11, 23].

Recurrence rate
Recurrence rate was not significantly different between laparoscopic and open IPOM. Our long-term results extend the findings of meta-analyses with shorter follow-up ranging between 0.2 and 2.9 years that revealed no difference in recurrence rate [12,24,25]. Furthermore, we show that the recurrence rate after either laparoscopic or open repair reaches a steady state at 4.7 years postoperatively. An overview of studies reporting recurrence rates after incisional hernia repair after a follow-up of at least 5 years is given in Fig. 5 to set our findings in the context to the existing literature [26][27][28][29][30][31][32][33][34][35][36][37].

Localization of hernia recurrence
Hernia recurrence after laparoscopic surgery was mainly observed in the epigastric region (EHS classification M2) of the median laparotomy scar. This might be because of difficulties to fix the mesh at the sternum and the ventral costal arch. Specifically after open incisional hernia repair, recurrence was additionally present in the flank (EHS classification L2) of the transverse laparotomy scar. Insufficient overlap at the transition to the retroperitoneum might be the reason. With its topographical maps of hernia recurrence, the study extends knowledge from the few previous studies, which described 18-29% of recurrences being offmidline [26,38].

Limitations
One limitation with this type of study is its limited rate of clinical follow-up because patients either were deceased, could not be contacted, or were unwilling to undergo clinical investigation at the time of recruitment. Another limitation of this study is its retrospective design with lack of randomization. Therefore, we used a propensity score matching approach to avoid selection bias.

Conclusion
This study eliminates the bias of mesh position for the comparison of laparoscopic versus open incisional hernia repair. Laparoscopic IPOM revealed shorter operation time, hospital stay, reduced complications, and SSI when compared to open IPOM. In long-term follow-up, hernia recurrence is common in both techniques and occurs until 5 years postoperatively, independent of the operation technique. Abet et al [28] Burger et al [29] Burger et al [29] Hawn et al [26] Hawn et al [26] Hawn et al [26] Iqbal et al [30] Kokotovic et al [31] Kokotovic et al [31] Kokotovic et al [31] Kurzer et al [32] Moreno-Egea et al [34] Rogmark et al [35] Sauerland et al [36] Sauerland et al [36] Tentes et al [37] Yaghoobi et al [38] Current study Current study n=100 n=250 n =500 n=1000 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.