Introduction

The open sublay mesh operation and the laparoscopic intraperitoneal onlay mesh (IPOM) repair are still the most widely used procedures for the treatment of primary and recurrent abdominal wall hernias worldwide [6,7,8]. However, both techniques have specific disadvantages and problems: the open techniques are burdened with larger wounds and higher rates of SSO and SSI. The laparoscopic IPOM repair with obligatory traumatic mesh fixation carries an increased risk of intraoperative bowel injury, adhesions, bowel obstruction, nerve injury, and acute and chronic pain [1,2,3,4,5,6,7,8,9]. Today, it is generally accepted, that the pre-peritoneal/retro-muscular (= sublay) plane is the best option for permanent mesh placement in hernia repair [6,7,8,9]. The last years have been characterized by a shift of paradigm in ventral and incisional hernia repair. Due to several publications with promising short-term results, the new minimally invasive techniques with extra-peritoneal mesh repair are becoming more and more popular [10,11,12,13,14,15,16,17,18,19,20]. Pioneering this trend, we started early to look for new techniques of minimal-invasive ventral hernia repair [11, 13,14,15, 18, 19]. For the reduction of complication rates and improvement of quality of life after ventral and incisional hernia repair, we developed the endoscopically assisted mini- or less-open sublay (E/MILOS) concept [13, 15, 18, 19].

Materials and methods

Endoscopically assisted (MILOS) and endoscopic mini- or less-open sublay (EMILOS) repair

Beginning in 2010, all MILOS and EMILOS (E/MILOS) incisional hernia operations were prospectively registered in the Herniamed Registry. The perioperative complication rates and 1-year follow-up data of this registry-based analysis were published in 2018 [18]. Figure 1 shows the flow chart of patient inclusion for the 5-year follow-up analysis. Only elective operations were included in the analysis. Mini-open and less-open access were defined as incisions of up to 5 cm and 12 cm, respectively, with a maximum incision length of less than one-fourth of the longest mesh diameter. Operations with incisions longer than 12 cm and/or an incision length/mesh diameter ratio of > 1/4 were excluded from the analysis. Small incisional hernias (< 1.5 cm defect diameter) had a suture repair. Primary outcome parameters were recurrence, pain at rest, pain on exertion, and chronic pain requiring treatment after 5 years. Secondary outcome variables were postoperative surgical complications and general complications. 5 years after the operation, all patients and the general practitioners received a questionnaire. If the patient and/or the general practitioner reported about any problem after the operation, the patient could be requested to attend clinical examination or radiologic tests. Pain was assessed by numerical rating scale (NRS, 0–10). The 5-year follow-up outcomes of E/MILOS incisional hernia operations at Gross-Sand Hospital were compared with laparoscopic IPOM and open sublay incisional hernia repair at all other institutions participating in the Herniamed Registry using propensity score matching [18, 22]. Only E/MILOS operations that had been included in the 1-year follow-up analysis [18] were eligible for the 5-year analysis.

Fig. 1
figure 1

Flow Chart for patient inclusion of analysis (Herniamed registry)

Full size image

A detailed description of the technical steps and perioperative management of the MILOS and endoscopic MILOS (= EMILOS) operation has already been published [13, 18, 19]. The MILOS operation is performed via a small skin incision trans-hernially with light-armed laparoscopic instruments either under direct vision or endoscopically assisted with gasless endoscopy [13, 18, 19]. After transhernial mini-open dissection of a small extraperitoneal space transhernial insertion of an optic port device, and CO2 insufflation, the procedure can be continued endoscopically (EMILOS) [13, 18, 19]. In lateral incisional hernias, the transhernial dissection is performed in the preperitoneal plane. In large hernias where after retromuscular dissection, a defect closure is not possible. An additional E/MILOS m. transversus abdominis release (TAR) is performed according to the principles of the open TAR procedure [23].

Statistics

All analyses were performed with the software SAS 9.4 (SAS Institute Inc., Cary, NC, USA) and intentionally calculated to a full significance level of 5%, that is, they were not corrected in respect of multiple tests, and each P ≤ 0.05 represents a significant result. The perioperative and the 5-year follow-up outcomes for MILOS incisional hernia operations at Gross-Sand Hospital were compared with laparoscopic IPOM and open sublay incisional hernia operations at all other institutions participating in the Herniamed Registry’ using propensity score matching [18, 22].

Propensity score matching was performed using greedy algorithm and a caliper of 0.2 standard deviations. The variables used for matching were: Hernia defect [cm2], sex, ASA score (I/II/III–IV), primary incisional hernia (yes/no), European Hernia Society (EHS) classification (width W1: 1–4 cm/W2: > 4 cm– < 10 cm/W3: > 10 cm), EHS lateral (yes/no), EHS medial (yes/no) [22], body mass index, age, oral anticoagulants (yes/no), platelet inhibitors (yes/no), preoperative pain (yes/no/unknown), and mesh size [cm2].

The balance of the matched sample was checked using standardized differences (also given for the pre-matched sample) that should not exceed 10% (< 0.1) after matching. For pairwise comparison of matching parameters between operation methods [for presenting the differences in the original (pre-matched) sample], x2 tests and t tests (Satterthwaite) were performed for categorical and continuous variables, respectively. For defect size [cm2] and mesh size [cm2], a logarithmic transformation was applied, and retransformed mean and range of dispersion are given.

Matched samples were then analyzed for perioperative and 5-year follow-up outcomes (intra- and postoperative complications, complication-related reoperations, pain at rest and on exertion, pain requiring treatment, and recurrences) via McNemar’s test. The results obtained are presented as the non-diagonal elements of the 2 × 2 frequency table, the corresponding p values, and the odds ratio (OR) estimates for matched samples with 95% confidence interval.

Results

In the Herniamed Registry 2511 laparoscopic IPOM procedures, 3170 open sub-lay and 538 E/MILOS incisional hernia operations with complete 5-year follow-up could be identified (Fig. 1), of which 138 (25.7%) were EMILOS operations. Eight patients had died within 5 years after surgery due to causes not related to E/MILOS repair. The E/MILOS cohort had a 5-year follow-up rate of 87.5%. For the comparison of E/MILOS repair with laparoscopic IPOM operation and E/MILOS operation with open sublay repair, propensity score matching analysis of 448 (83.3%) and 520 (96.7%) patient pairs was possible, respectively. The cohorts were well balanced for all matching parameters (Figs. 2 and 3).

Fig. 2
figure 2

E/MILOS versus Laparoscopic IPOM operation: Scatter Plot: Standardized differences for matching variables both before (original sample) and after matching (matched sample)

Full size image
Fig. 3
figure 3

E/MILOS versus Open sublay Operation: Scatter Plot: Standardized differences for matching variables both before (original sample) and after matching (matched sample)

Full size image

Matched pair analysis of E/MILOS versus laparoscopic IPOM operation

Continuous matching parameters:

The descriptive statistics of age, BMI, defect sizes, and mesh sizes of the E/MILOS versus laparoscopic IPOM cohort before matching are given in Table 1.

Table 1 E/MILOS versus Laparoscopic IPOM operation: summary of descriptive statistics and results of the unadjusted tests for homogeneity between comparison groups for the continuous matching variables before matching
Full size table

Mean defect sizes of the E/MILOS and laparoscopic IPOM cohort with complete 5-year follow-up are 44.6 cm2 (range 40.4–48.7 cm2) and 21.7 cm2 (range 18.0–25.3 cm2), respectively.

Mean mesh sizes E/MILOS, and laparoscopic IPOM are 494.2 cm2 (range 492.2–496.1 cm2), and 279.3 cm2 (range 277.4–281.2 cm2), respectively.

Categorical matching parameters:

The descriptive statistics of gender, ASA score distribution, hernia size and location according to the EHS incisional hernia classification, patients with preoperative pain, primary incisional hernia operations, and rate of operations performed under anticoagulation medication of the E/MILOS versus laparoscopic IPOM cohort before matching are shown in Table 2.

Table 2 E/MILOS versus laparoscopic IPOM operation: summary of descriptive statistics and results of unadjusted tests for homogeneity between comparison groups for the categorical matching variables before matching
Full size table

In the E/MILOS cohort, there were 412 (76.6%) medial, 56 (10.4%) lateral, and 70 (13.0%) combined hernias. The number of W1, W2, and W3 incisional hernias was 93 (17.3%), 246 (45.7%), and 199 (37.0%), respectively.

Propensity score matching:

Propensity score matching was performed using greedy algorithm and a permitted caliper width of 0.2 standard deviations for the 538 E/MILOS and the 2511 laparoscopic IPOM patients. Matching was successfully performed for n = 448 (83.3%) patients.

Figure 2 shows the standardized differences between the matching variables both before (original sample) and after (matched sample) matching.

That difference was well below 10% for all matching variables, attesting a good balance between the groups for the variables included in the model.

Compared with laparoscopic IPOM incisional hernia operation, the E/MILOS repair was associated with fewer postoperative surgical complications [1.8% vs 4.2%, P = 0.052; OR = 0.421 (0.159, 1.007)], significantly fewer general complications [0.7% vs 3.6%, P = 0.004; OR = 0.187 (0.035, 0.655)], significantly less recurrences after 5 years [0.9% vs 5.6%, P < 0.001; OR = 0.160 (0.040, 0.463)], including cumulative recurrences after 1 year and 5 years [2.7% vs 8.9%, P < 0.001; OR = 0.300 (0.143, 0.583)], less chronic pain at rest after 5 years [2.9% vs 5.8%, P = 0.053; OR = 0.500 (0.236, 1.009)], significantly less chronic pain on exertion [2.9% vs 10.7%, P < 0.001; OR = 0.271 (0.135, 0.508)], and significantly less chronic pain requiring therapy [1.8% vs 4.9%, P = 0.016; OR = 0.364 (0.140, 0.848)]. Results are shown in Table 3.

Table 3 Mini-Open sublay versus Laparoscopic IPOM: Results of matched pair analysis of incisional hernia repair (448 matched pairs)
Full size table

Matched pair analysis of E/MILOS versus open sublay operation

Continuous matching parameters:

The descriptive statistics of age, BMI, defect sizes, and mesh sizes of the E/MILOS versus open sublay cohort before matching are shown in Table 4:

Table 4 E/MILOS versus open sublay operation: summary of descriptive statistics and results of the unadjusted tests for homogeneity between comparison groups for the continuous matching variables before matching
Full size table

Mean defect sizes of the E/MILOS and open sublay cohort with complete 5-year follow-up are 44.6 cm2 (range 40.4–48.7 cm2), and 30.5 cm2 (range 27.0–34.1 cm2), respectively.

Mean mesh sizes the E/MILOS and open sublay cohort are 494.2 cm2 (range 492.2–496.1 cm2) and 250.1 cm2 (range 247.8–252.5 cm2), respectively.

Categorical matching parameters:

The descriptive statistics of gender, ASA score distribution, hernia size and location according to the EHS incisional hernia classification, patients with preoperative pain, primary incisional hernia operations, and rate of operations performed under anticoagulation medication of the E/MILOS versus open sublay cohort before matching are given in Table 5.

Table 5 E/MILOS versus Open sublay operation: Summary of descriptive statistics and results of unadjusted tests for homogeneity between comparison groups for the categorical matching variables before matching
Full size table

Propensity score matching:

Propensity score matching was performed using greedy algorithm and a permitted caliper width of 0.2 standard deviations for the 538 E/MILOS and the 3170 open sublay patients. Matching was performed for n = 520 (96.7%) patients. Figure 3 shows the standardized differences between the matching variables both before (original sample) and after (matched sample) matching.

That difference was well below 10% for all matching variables, attesting a good balance between groups for the variables included in the model.

After E/MILOS repair, there were fewer postoperative complications [2.1% vs 16.5%, P < 0.001; OR = 0.128 (0.062, 0.240)], fewer general complications [1.0% vs 5.2%, P < 0.001; OR = 0.185 (0.056, 0.488)], less recurrences after 5 year [1.0% vs 3.5%, P = 0.011; OR = 0.278 (0.081, 0.776)], less cumulative recurrences after 1 year and 5 years [2.7% vs 7.1, P = 0.002; OR = 0.378 (0.189, 0.717)], less chronic pain after 5 year at rest [3.1% vs 7.3%, P = 0.004; OR = 0.421 (0.219, 0.773)], on exertion [3.9% vs 12.3%, P < 0.001; OR = 0.313 (0.179, 0.523)], and less chronic pain requiring therapy [2.5% vs 5.8%, P = 0.014; OR = 0.433 (0.207, 0.856)]. All differences were statistically significant. Results are shown in Table 6.

Table 6 Mini-Open sublay versus Open sublay: Results of matched pair analysis of incisional hernia repair (520 matched pairs)
Full size table

Discussion

Incisional hernia repair is among the most frequent operations in general and abdominal surgery [8]. The most widely used techniques are still open retro-muscular mesh and laparoscopic IPOM repair [8], but the new minimal-invasive techniques with extra-peritoneal mesh placement are gaining popularity [8, 10,11,12,13,14,15,16,17,18,19,20].

To our knowledge, this is the first trial reporting on long-term results of the new minimal-invasive extra-peritoneal mesh repair techniques (E/MILOS, eTEP, TARM, laparoscopic TAPP, and robotic-assisted variants).

The short-term results with one-year follow-up of this prospective Herniamed registry trial revealed significantly less perioperative complications, recurrences, and chronic pain after E/MILOS vs laparoscopic IPOM and open Sub-lay repair [18]. The promising early results are confirmed by our 5-year follow-up propensity score matching analysis: there are significantly less recurrences, less cumulative recurrences (includes recurrences in 1-year follow-up), late postoperative complications, and patients suffering from chronic postoperative pain after E/MILOS operations compared to open Sub-lay and laparoscopic IPOM repair (Figs. 2 and 3; Tables 3 and 6).

In this propensity score matching trial, the long-term cumulative recurrence rates after laparoscopic IPOM and open Sub-lay repair are 8.9% and 7.1%, respectively.

We detected 12 trials with long-term follow-up (48–84 months) after incisional hernia repair: one RCT, two register trials, and 9 retrospective cohort trials. The evidence of most of these studies is low [8, 32,33,34,35,36,37,38]. The only long-term RCT reported on incisional hernia repair, compared suture with open retro-muscular mesh repair. There were more recurrences (63% vs 32%; P < 0.001) and more chronic abdominal pain after suture repair (36% vs 20%; P = 0.01) indicating the superiority of mesh repair [32].

Nine publications with long-term follow-up after open retro-muscular mesh repair with a total of 2.376 patients reported recurrence rates between 5 and 34% [32,33,34,35]. A retrospective cohort trial from Sweden found a recurrence rate of 8.1% 7 years after open retro-muscular mesh repair, which is in accordance with our results. The trial also investigated long-term quality of life. The authors concluded that hernia recurrence and chronic postoperative pain have the highest impact on the hernia-related quality of life [34].

The long-term (54 to 78 months of follow-up) recurrence rates after laparoscopic IPOM incisional hernia repair in three cohort trials ranged between 4.5 and 20%. [36,37,38].

A long-term prospective register study of the Danish Hernia database which included all 3242 elective incisional hernia operations in Denmark from 2007 to 2010 with a median follow-up period of 60 months and 100% follow-up rate reported recurrence rates after open mesh and laparoscopic IPOM repair of 12.3% and 10.6%, respectively. The mesh-related complication rates after open mesh and laparoscopic mesh repair were 5.6% and 3.7%, respectively [33]. In contrast to this finding, there were no reports of late mesh-related complications, bowel obstructions, mesh infections, fistulae, and mesh-related reoperations in the 5-year follow-up after E/MILOS operation. In our series, two large chronic subcutaneous seromas after repair of large midline incisional hernias were successfully treated in mini-open technique. There were no reoperations related to chronic pain in our cohort.

The evidence of long-term chronic pain after incisional hernia repair in the literature is very low [8, 32,33,34,35,36,37,38].

Only one register trial had a higher long-term follow-up rate than 87.5% in our E/MILOS cohort [33] and only two register trials included more patients in the long-term follow-up than our study [33, 34]. All previous long-term trials on incisional hernia repair reported higher recurrence and chronic pain rates compared to our results after E/MILOS operations [32,33,34,35,36,37,38]. Due to the heterogeneity of trials, these findings should be interpreted carefully.

Even though very large incisional hernias were excluded and operated on with an open sublay repair, the E/MILOS cohort of this propensity score matching analysis included a considerable percentage of incisional hernias which can be considered as difficult or complex: There were more than two thirds recurrent incisional hernias, 37% large incisional hernias (W3 EHS classification), and 23.2% lateral or combined (EHS classification: L, LM) incisional hernias, Tables 2 and 5). Moreover, in our cohort, 40.2% of the patients had BMI > 30, indicating that the E/MILOS operation is also suitable for obese patients. In obese patients, the incision may have to be one to two cm larger, compared to normal weight patients. In this study, we performed an EMILOS repair in one-quarter of the cases. Detailed indications and results of MILOS and EMILOS operations, including E/MILOS TAR operations were published previously [18]. In the first phase of this trial, there was no difference in outcomes between MILOS and EMILOS repair [18]. Because of this finding, we did not perform a subgroup analysis between MILOS and EMILOS operations after 5 years. In 79.3% of our cases, video endoscopy was used. Those operations can be considered as hybrid operations [18].

The mini-open transhernial approach avoids damage of intact structures of the abdominal wall, allows extended dissection in the retromuscular/preperitoneal plane, implantation of large standard meshes with a wide defect overlap (Table 1 and 4) without traumatic mesh fixation, facilitates hernia sac manipulations, defect closure and skin/scar corrections. This reduces the risk of recurrences, bulging, visceral adhesions, bowel lesions, nerve damage with acute and chronic pain.

Since long-term results of the other new MIS techniques have not been published, a comparison with E/MILOS data is not yet possible. Compared to the new pure laparoendoscopic techniques (ventral hernia eTEP, TARM, TAPP, and robotic variants), the mini-open transhernial approach may allow easier dissection of large hernia sacs (especially if bowel or omentum is incarcerated), easier mesh insertion, defect closure, skin and scar corrections, and umbilical reconstruction. Pure laparoendoscopic closure of large defects without mini- or less-open skin and scar corrections may result in ugly folding and bulging of the skin.

The E/MILOS operation is associated with a low number of short-term SSOs and SSIs [18, 19]. In this analysis, there were no late infections detected.

The finding that infection rates after laparoscopic IPOM and E/MILOS repair are in the same low range [18, 19] is in accordance with other recent publications that compared new hybrid MIS techniques of ventral and incisional hernia repair with pure laparoendoscopic and open procedures [22,23,24,25,26,27,28,29,30,31].

In contrast to other innovative surgical procedures like robotic ventral hernia repair, the E/MILOS operation does not require expensive instruments and devices. The reusable light source for laparoscopic instruments (Endotorch TM, Fa. Richard Wolf, Knittlingen) and retractors cost approximately 2.500,-€. Compared with laparoscopic IPOM repair, every E/MILOS operation saves about 1.200,-€ in material costs as no meshes with adhesion barrier and no mesh fixation devices are needed. Discussing operation costs, a disadvantage of the E/MILOS operation in this trial must be mentioned: the operation time was 8 and 21 min longer compared to open sublay and laparoscopic IPOM repair, respectively [18].

Limitations of this trial: For 1- and 5-year follow-up, a questionnaire is sent to the patient and general practitioner, asking both about any recurrence, bulging, pain at rest, pain on exertion, and chronic pain requiring treatment. If recurrence or chronic pain is reported by the general practitioner or patient, patients could be requested to attend clinical examination or radiologic tests. Nevertheless, asymptomatic recurrences may be missed. There is a bias because the results of E/MILOS incisional hernia operations are from a high-volume referral hernia center as compared with laparoscopic IPOM and open sublay operations data from all institutions participating in the German Hernia registry.

The low 5 years of follow-up rate after laparoscopic IPOM and open sublay operation is a further limitation of this study. At least, we can quantify the differences between those patients with a 5-year follow-up (n = 6219) and those without (n = 10,799): the standardized differences between those two groups are below 10% (as a role of thumb) for general and postoperative complications as well as for all matching variables except for age and mesh size. Here, patient groups differ by 1.6 years and 24 cm2, respectively. Thus, matching variables and perioperative outcomes are quite balanced between patients with and without a 5-year follow-up so that we conclude that we have no relevant bias in the analysis population (Fig. 4).

Fig. 4
figure 4

Standardized differences of the infuencing factors and the perioperative outcomes between patient collectives with and without follow-up

Full size image

In 2017 after the end of patient enrollment of this trial, we modified the EMILOS technique to allow a faster begin of the endoscopic operation phase, using flexible wound protection devices with a cap and opening for standard camera ports. Technical details were published previously [19]. Since 2017, our EMILOS technique is unchanged and now used in two-third of our incisional hernia operations.

This prospective register trial with propensity score matching shows that hernia registries may play an important role in the development, evaluation, and successful implementation of new surgical techniques.

Conclusion

The E/MILOS repair allows the minimal-invasive sublay repair of almost all incisional hernias with low long-term morbidity. Compared with open sublay and laparoscopic IPOM repair, the E/MILOS operation is associated with significantly fewer long-term complications, less chronic pain, and less recurrences after five years. In our hands, the technique is reproducible, easy to standardize, and combines the advantages of open sublay and laparoscopic IPOM repair. Our favorable results have to be confirmed by future high-quality register trials and multicenter RCTs.