Open Intraperitoneal Onlay Mesh (IPOM) Technique for Incisional Hernia Repair

In an Expert Consensus Guided by Systematic Review the panel agreed that for open elective incisional hernia repair sublay mesh location is preferred, but open intraperitoneal onlay mesh (IPOM) may be useful in certain settings. Accordingly, the available literature on the open IPOM technique was searched and evaluated. Material and Methods: A systematic search of the available literature was performed in July 2018 using Medline, PubMed, and the Cochrane Library. Forty-five publications were identified as relevant for the key question. Results: Compared to laparoscopic IPOM, the open IPOM technique was associated with significantly higher postoperative complication rates and recurrence rates. For the open IPOM with a bridging situation the postoperative complication rate ranges between 3.3 and 72.0% with a mean value of 20.4% demonstrating high variance, as did the recurrence rate of between 0 and 61.0% with a mean value of 12.6%. Only on evaluation of the upward-deviating maximum values and registry data is a trend toward better outcomes for the sublay technique demonstrated. Through the use of a wide mesh overlap, avoidance of dissection in the abdominal wall and defect closure it appears possible to achieve better outcomes for the open IPOM technique. Conclusion: Compared to the laparoscopic technique, open IPOM is associated with significantly poorer outcomes. For the sublay technique the outcomes are quite similar and only tendentially worse. Further studies using an optimized open IPOM technique are urgently needed.


INTRODUCTION
Two recently published systematic reviews and meta-analyses and a registry study once again impressively demonstrated that for incisional hernias mesh techniques compared with suture techniques resulted in significantly lower recurrence rates (1)(2)(3). However, which mesh technique assures the best outcomes for the respective patient is still under debate.
In an Expert Consensus Guided by Systematic Review the panel agreed that for open elective incisional hernia repair sublay mesh location is preferred, but open intraperitoneal onlay mesh (IPOM) may be useful in certain settings (13). In systematic reviews the open IPOM technique is discussed, in particular, in the context of large incisional hernias (14,15). Based on the expert consensus, this paper now explores and evaluates the available literature on open intraperitoneal onlay mesh (IPOM) in accordance with the Parker (16) nomenclature.

MATERIALS AND METHODS
A systematic search of the available literature was performed in July 2018 using Medline, PubMed, and the Cochrane Library, as well as a search of relevant journals and reference lists. The following search terms were used: "Incisional hernia, " "Intraperitoneal mesh, " "Open intraperitoneal onlay mesh, " "Open IPOM, " and "IPOM." The abstracts of 423 publications were checked. For the present analysis 45 publications were identified as relevant for the key question (Figure 1).
Similarly, the retrospective comparative study of 120 laparoscopic and 64 open IPOM operations showed comparable outcomes (18), with a significantly lower postoperative complication rate in favor of the laparoscopic technique (10 vs. 23%; p = 0.046) (18). Similarly, in this study the hospital stay after laparoscopic IPOM was significantly shorter [median 6 (4-7) days vs. 8 (5)(6)(7)(8)(9)(10)(11)(12) Table 2). The outcomes demonstrated high variance ( Table 2). The postoperative complication rates were in the range of 3.3-72% and the recurrence rates 0-61%. The mean value calculated for the open intraperitoneal onlay mesh technique in the studies featured in Table 2 was 20.4% (range: 3.3-72%) for the postoperative complication rates and the recurrence rates it was 12.6% (range: 0-61%). Some studies revealed extremely good (postoperative complication rate 7%, recurrence rate 10%) (24), others extremely poor (postoperative complication rate 72%, recurrence rate 61%), outcomes (25).The authors of the publication with the best outcomes attributed the good results to the use of a wide overlap, avoidance of dissection in the abdominal wall and coverage of the mesh with the peritoneal hernia sac or defect closure (24 After excision of the scar, the herniated sac is exposed and the adjacent anterior fascia is cleared of subcutaneous tissue up to 10-15 cm from the ring of the hernia sac. The sac is then excised and intestinal adhesions dissected free to facilitate the placement of the mesh at least 10 cm from the edge of the hernia neck. The mesh is secured to the musculofascial wall by through-and-throughnon absorbable sutures" (30). "The anterior lamina of the rectus sheath is incised longitudinally 4 cm back from its medial edge bilaterally. Both aponeurotic flaps are then reflected inward and sutured by interrupted absorbable stitches" (30). The publications addressing this technique report much lower postoperative complication rates and recurrence rates (30-32) (  (33). "Skin and subcutaneous flaps are then developed on both sides to allow for medialization of the rectus muscles and fascia over the mesh" (33). "The mesh is placed within the abdomen and secured with u-sutures" (33). The fascia and excess hernia is then closed over the mesh" (33). "This also allows for return of the rectus muscles to the midline thus restoring the normal architecture of the abdominal wall" (33). The outcomes with this technique ( Table 4) are also highly variable and no better than those achieved with the modification involving the myoaponeurotic flap (33,34).

Open Intraperitoneal Onlay Biological Mesh With Defect Closure by a Component Separation Technique in Contaminated Ventral and Incisional Hernias
In a prospective multicenter study on repair of contaminated ventral hernias, 26 patients were treated by means of a component separation technique and intraperitoneal placement  of a biological mesh (Strattice) (35). All patients had a defect closure and reinforcement of the repair with an appropriately sized piece of a biologic mesh with at least 3-5 cm of fascial overlap (35). The rate of wound infection was 30%, wound dehiscence 15%, seroma 15% and hematoma 8% (35). The recurrence rate after 1 year was 30%. No significant differences were noted vs. positioning of the biological mesh in the retrorectus layer (35).

Assessment of the Open Intraperitoneal Onlay Mesh Technique in Systematic Reviews and Meta-Analyses
In a Cochrane database systematic review comparison of onlay vs. intraperitoneal mesh position in open incisional hernia repair revealed that there were non-significantly fewer hernia recurrences, less seroma formation and more postoperative pain in the intraperitoneal group (37).
The findings of three further systematic reviews and metaanalyses must be analyzed in a critical light with respect to the key question addressed here since they included studies with primary abdominal wall hernias and incisional hernias, i.e., mixed patient collectives, as well as the laparoscopic technique (38)(39)(40). Numerous studies have demonstrated that the outcomes for repair of primary abdominal wall hernias and incisional hernias differ highly significantly and therefore should not be combined (41)(42)(43)(44)(45). Moreover, the mesh position as underlay was not defined exactly. These may also have included preperitoneal mesh placements (16). Studies with biological meshes were also included (38).

Mean Values of Postoperative Complications and Recurrence Rate
Under consideration of all analyzed studies the mean value for the postoperative complications is 20.4% with a range of 3.3 and 72% and for the recurrence rate 12.6% with a range of 0-61%.

DISCUSSION
While in an Expert Consensus Guided by Systematic Review preference is given to the sublay mesh position for repair of incisional hernia, the open intraperitoneal onlay mesh (IPOM) technique is, nonetheless, deemed useful in certain clinical situations (13). Therefore, this present review of the literature collates and analyzes the data available on the open IPOM technique. Comparison of the open with the laparoscopic technique reveals significant advantages for the laparoscopic procedure. Since in the guidelines the use of the laparoscopic IPOM technique is recommended only for a defect size of up to 10 cm (8)(9)(10)(11)(12), laparoscopic repair should be given preference for defects up to that size. Accordingly, the open IPOM technique in addition to other procedures tends to be used for large incisional hernias (14,15). In general defect closure of large incisional hernias is not possible, thus creating a bridging situation as reported on in the majority of studies on the open IPOM. The outcomes demonstrate high variance. For example, for open IPOM with bridging situation postoperative complication rates of between 3.3 and 72.0% and mean value of 20.4% are identified, and for the recurrence rate of between 0 and 61.0% with mean value of 12.6%.The outcomes are very diverging. These inconsistent outcomes are probably explained by the fact that the open IPOM technique represents a very heterogeneous group. In some cases, the results derive from centers and surgeons dedicated to refining the technique, using it as the first-hand choice with great volume and awareness of the anatomical circumstances [e.g., (19-24, 26, 28, 30-32)]. In other cases, the open IPOM is applied as a desperate solution to solve a complex problem when there is no other alternative due to anatomical conditions after previous surgery [presumably references (2,4,17,18,36,39)].
Comparison of these findings with the outcomes reported in the literature for sublay repair of incisional hernia reveals that in the case of the sublay technique the postoperative complication rates are between 8.0 and 26.0%, with a mean value of 18.6%, and recurrence rates of between 1.6 and 32.0%, with a mean value of 13.5% (29). Hence, only in respect of the extreme values are the outcomes better for the sublay technique. Likewise, registry data demonstrate somewhat more favorable outcomes for the sublay technique.
Therefore, further comparative studies are urgently needed to ascertain the role of the open IPOM technique in incisional hernia repair. That is borne out in particular in the study by Iannitti et al. (24) with a large sample size (n = 455) and a low postoperative complication rate of 7% and recurrence rate of 1% at a mean follow-up of 29.3 months. In the technique described by Iannitti et al. (24) dissection in the abdominal wall was avoided and attention paid to the provision of an appropriately large mesh overlap. Furthermore, the mesh was covered with at least the peritoneal hernia sac (24).
Attention should be paid to these technical aspects when implementing the open IPOM technique.
Modifications of the open IPOM technique are aimed at mesh-based defect closure through a combination with a myoaponeurotic flap or closure of the anterior lamina of the rectus sheath as used in the sublay technique. However, both techniques require dissection in the abdominal wall, albeit to a lesser degree when using myoaponeurotic flaps. That also no doubt explains the more favorable outcomes of open IPOM repair by means of a myoaponeurotic flap compared with closure of the anterior lamina of the rectus sheath. Likewise, comparison of outcomes of open IPOM technique with bridging reveals lower postoperative complication and recurrence rates for the modification with myoaponeurotic flaps. However, to date that technique has only been used and extensively reported by a French working group.
From the available meta-analyses and systematic reviews it is almost impossible to generate further data on open IPOM outcomes since they include joint evaluation of primary abdominal wall hernias and incisional hernias, open and laparoscopic techniques as well as synthetic and biological meshes. Hence, interpretation of outcomes is very difficult.
In summary, it can be stated that the open IPOM is clearly inferior to the laparoscopic technique but achieves quite acceptable outcomes compared with the open sublay technique. It appears that outcomes can be further improved through the use of a wide overlap, avoidance of dissection in the abdominal wall and defect closure. Further studies using a standardized open IPOM technique are urgently needed.

AUTHOR CONTRIBUTIONS
FK: literature search, literature analyses, publication concept, and publication draft; BL: literature search, literature analyses, publication concept, and critical review of the publication draft.