Prevention of Adhesion to Prosthetic Mesh

Abstract

Objective

To assess whether use of antiadhesive liquids or coatings could prevent adhesion formation to prosthetic mesh.

Summary Background Data

Incisional hernia repair frequently involves the use of prosthetic mesh. However, concern exists about development of adhesions between viscera and the mesh, predisposing to intestinal obstruction or enterocutaneous fistulas.

Methods

In 91 rats, a defect in the muscular abdominal wall was created, and mesh was fixed intraperitoneally to cover the defect. Rats were divided in five groups: polypropylene mesh only (control group), addition of Sepracoat or Icodextrin solution to polypropylene mesh, Sepramesh (polypropylene mesh with Seprafilm coating), and Parietex composite mesh (polyester mesh with collagen coating). Seven and 30 days postoperatively, adhesions were assessed and wound healing was studied by microscopy.

Results

Intraperitoneal placement of polypropylene mesh was followed by bowel adhesions to the mesh in 50% of the cases. A mean of 74% of the mesh surface was covered by adhesions after 7 days, and 48% after 30 days. Administration of Sepracoat or Icodextrin solution had no influence on adhesion formation. Coated meshes (Sepramesh and Parietex composite mesh) had no bowel adhesions. Sepramesh was associated with a significant reduction of the mesh surface covered by adhesions after 7 and 30 days. Infection was more prevalent with Parietex composite mesh, with concurrent increased mesh surface covered by adhesions after 30 days (78%).

Conclusions

Sepramesh significantly reduced mesh surface covered by adhesions and prevented bowel adhesion to the mesh. Parietex composite mesh prevented bowel adhesions as well but increased infection rates in the current model.

Incisional hernias occur in 5% to 20% of patients after abdominal surgery. ^1–4 In incisional hernia repair, the introduction of tension-free techniques by using prosthetic material has reduced recurrence rates from up to 50% to less than 24%. ^5–9 However, foreign materials, such as prosthetic mesh, represent a strong stimulus for the development of permanent adhesions. ¹⁰ Particularly if the mesh is placed intraperitoneally, concern exists about development of adhesions between bowel and mesh. These adhesions can cause serious complications, such as intestinal obstruction and enterocutaneous fistulas. ^11–14

The aim of the present study was to assess whether adhesions due to intraperitoneal mesh can be prevented by the use of physical barriers that can be applied laparoscopically. For this purpose, we assessed if intraperitoneal administration of liquid physical barriers composed of hyaluronic acid (Sepracoat, HAL-C; Genzyme Corp., Cambridge, MA) or Icodextrin solution (Extraneal, Baxter Healthcare Inc.) could prevent adhesions to a polypropylene mesh without interfering with wound healing and tissue incorporation of the mesh. In addition, we studied the ability of specifically coated meshes, Sepramesh (Genzyme) and Parietex composite mesh (Sofradim, France), to prevent adhesions.

METHODS

Animals

Ninety-one male inbred rats of the Wistar strain (weight 250–300 g) were obtained from Harlan (Zeist, The Netherlands). They were bred under specific pathogen-free conditions, kept under standard laboratory conditions (temperature 20–24°C, relative humidity 50–60%, 12 hours light/12 hours dark), and fed with laboratory diet (Hope Farms, Woerden, The Netherlands) and water ad libitum. The experimental protocol adhered to rules set by the Dutch Animal Experimentation Act and was approved by the Committee in Animal Research of the Erasmus University Rotterdam. Nonpowdered gloves were used routinely in the experimental procedure.

Operative Procedure

Following initial sedation with ether, each animal received an intraperitoneal injection of 0.15 mL ketamine (100 mg/mL) and 0.04 mL xylazine (20 mg/mL). The abdomen was shaved and cleaned with alcohol 70%.

The experiments were performed in a validated rat model described by Alponat et al. ¹⁵ and Hooker et al. ¹⁶ In all animals, laparotomy was performed using a midline incision of 4 cm. Skin flaps were raised and a standardized 1.5 × 2.5-cm longitudinal full-thickness defect consisting of fascia, muscle, and peritoneum was created.

Experiments

Experiment 1

In 20 rats, the defect of the abdominal wall was repaired with a polypropylene mesh (Prolene, Ethicon Inc., Somerville, NJ) measuring 2.5 × 3.5 cm that was fixed intraperitoneally with eight interrupted Prolene 5-0 sutures. Subsequently, the rats were randomized between no additional treatment (control group, n = 10) and addition of 4 mL Sepracoat solution (n = 10) intraperitoneally. In all animals, the skin was closed with continuous 4-0 polyglactin suture (Vicryl, Ethicon). Seven days postoperatively, adhesions were scored.

Experiment 2

In 20 rats, the defect of the abdominal wall was repaired with a polypropylene mesh (Prolene) measuring 2.5 × 3.5 cm that was fixed intraperitoneally with eight interrupted Prolene 5-0 sutures. After placement of the mesh, the rats were randomized between no additional treatment (control group, n = 10) and addition of 4 mL Icodextrin 7.5% solution (Extraneal) intraperitoneally (n = 10). In all animals, the skin was closed with continuous 4-0 polyglactin suture (Vicryl, Ethicon). To prevent leakage of the liquid Icodextrin solution, the skin of the animals was additionally closed with Histoacryl glue. Seven days postoperatively, adhesions were scored.

Experiment 3

Thirty rats were randomly divided into three groups. In group 1 (n = 10), the defect was repaired with a polypropylene mesh (Prolene) measuring 2.5 × 3.5 cm. In group 2 (n = 10) the defect was repaired with a polypropylene mesh, coated with hyaluronic acid and carboxymethylcellulose on the visceral side of the mesh (Sepramesh). In group 3, the defect was repaired with a polyester mesh with a collagen coating on the visceral side (Parietex composite mesh) Meshes were fixed intraperitoneally with eight interrupted Prolene 5-0 sutures and the skin was closed with continuous 4-0 polyglactin suture (Vicryl, Ethicon). Seven days postoperatively, adhesions were scored.

Experiment 4

Experiment 4 was identical to experiment 3, but adhesions were assessed after 30 days instead of 7 days.

Scoring of Adhesions, Infection, and Incorporation

Seven or 30 days postoperatively, all rats were killed and underwent autopsy. A median skin incision was created and the abdominal cavity was entered through a U-shaped incision, extending caudal and lateral to the mesh. The presence of adhesions between bowel and the mesh was assessed. For each rat it was documented whether bowel adhesions were present. After that, the mesh was excised and both bowel and omental adhesions were sharply cut. The surface of the mesh that was covered by bowel and/or omental adhesions was assessed (Fig. 1). For this purpose, the mesh surface was divided into six sections. Each section was subsequently subdivided in six fields, and for each field the percentage of the surface covered by adhesions was estimated. Density of adhesions was scored according to Zühlke classification. ¹⁷ Infection was defined as pus coming from the mesh and wound. Incorporation of the prosthesis in the abdominal wall was scored by dividing the circumference of the mesh into 10 segments and subsequently determining the number of segments in which the mesh was not incorporated in the abdominal wall. Two independent investigators, who were unaware of the group assignment of the rats, performed scoring of adhesions and incorporation. In case of interobserver variance, the mean was scored.

Figure 1. Dense bowel adhesion to the mesh.

Histology

Of each group, three meshes with the adjoining abdominal wall were fixed in 10% neutral buffered formalin for at least 1 hour. After routine tissue processing, sections were cut at 4 to 6 μm and stained with hematoxylin and eosin. Sections were microscopically studied, and incorporation of the mesh in the surrounding tissue and inflammatory reaction were assessed for each group. The grade of inflammation was assessed using a semiquantitative scoring system, the inflammation grading scale. ¹⁶ Grade 1 on this scale represents a mild inflammatory reaction with giant cells, occasional scattered lymphocytes, and plasma cells. Grade 2 represents a moderate reaction with giant cells and increased admixed lymphocytes, plasma cells, eosinophils, and neutrophils. Grade 3 represents a severe inflammatory reaction with microabscesses present.

Statistical Analysis

Statistical analysis was performed using the Mann-Whitney test for independent samples. P < .05 was considered statistically significant.

RESULTS

Two animals died before the end of the experiment on postoperative days 4 and 5 of unknown causes (experiment 3). In all animals, adhesions of the omentum to the prosthetic mesh were seen to some extent. These adhesions could be lysed only by sharp dissection (Zühlke classification 3). ¹⁷ No herniations of viscera between mesh and abdominal wall were seen.

With polypropylene mesh, bowel adhesions to the mesh were seen in 50% to 60% of all animals. After 7 days, a mean surface of 74% to 88% of the mesh was covered by adhesions (Table 1). Instillation of Sepracoat solution in the peritoneal cavity did not significantly reduce the surface of the polypropylene mesh that was covered by adhesions (68% vs. 82%, P = .07) and did not prevent bowel adhesions to the mesh. Instillation of Icodextrin 7.5% solution did not reduce the surface of the mesh that was covered by adhesions, either (90% vs. 88%). Further, Icodextrin solution had no influence on the formation of bowel adhesions to the mesh.

Table 1.ADHESION FORMATION AND MESH INCORPORATION

Comparison of mean % of mesh surface covered by adhesions at 7 and 30 days postoperatively (experiment 3 vs. 4): *P = .01,

§P = .02, P = NS.

When Sepramesh was used, a significant reduction in the mean percentage of mesh surface covered by adhesions was found after 7 days (55% vs. 74%, P = .01), as well as after 30 days (25% vs. 48%, P = .03), compared to the control group. In addition, none of the animals with Sepramesh developed adhesions between bowel and the mesh, compared to 57% of the animals with polypropylene mesh (P = .04).

With Parietex composite mesh, there were no bowel adhesions to the mesh, either (P = .04). However, in the Parietex composite group, the infection rate was 57% at 30 days postoperatively compared to 0% in the control group (P = .02). In addition, the percentage of mesh surface covered by adhesions was higher in the Parietex composite group (78%) than in the control group (48%, P = .03).

Histologic evaluation in each control group showed foreign body reaction with giant cells and increased admixed lymphocytes, plasma cells, eosinophils, and neutrophils (grade 2 on the inflammation grading scale). A comparable reaction was found in the groups with the addition of Sepracoat or Icodextrin to a polypropylene mesh and in the group with Sepramesh (Fig. 2). However, in the group with Parietex composite mesh, a more severe inflammatory reaction was found, with the presence of many admixed inflammatory cells and microabscesses (grade 3 on the inflammation grading scale). Incorporation of the mesh was similar in all study groups.

Figure 2. Light microscopy of histology 7 days postoperatively with polypropylene mesh (A), Sepramesh (B), and Parietex composite mesh (C).

DISCUSSION

The reduction of recurrence rates following reinforcement of the abdominal wall by mesh in incisional hernia has promoted the use of mesh. ⁹ Polypropylene is most commonly used because it is easy to handle and relatively low in cost. Because polypropylene causes a pronounced and persistent inflammatory reaction, the mesh is well incorporated in the surrounding tissue of the abdominal wall. However, for the same reason, polypropylene causes a strong stimulus for the formation of adhesions. ^18–20

Adhesion formation is part of the normal healing process and is observed following 90% to 100% of all abdominal surgical procedures. ^21,22 Surgical trauma and foreign body reaction inhibit plasminogen activator activity. This inhibition is followed by reduced fibrinolysis, which results in increased deposition of fibrin matrix. ^23,24 The fibrin matrix gradually matures into an organized fibrous adhesion over the course of approximately 5 days. ²⁵ With time, the extent of adhesions decreases by approximately 30%, as was found in the present study (experiment 4 vs. experiments 1, 2, and 3). ²⁶

In the rat, intra-abdominal adhesions form within 24 hours after the operation, and after 7 days no new adhesions are formed. ^18,27 Therefore, adhesion formation in the present study was evaluated after 7 days. In the experiments with the coated meshes, adhesion formation was also assessed after 30 days to evaluate the antiadhesive effect after resolution of the coating.

Liquid Antiadhesive

Sepracoat is a viscous solution composed of 0.4% hyaluronic acid in phosphate-buffered saline. Hyaluronic acid is a glycosaminoglycan that is naturally found in the human body in connective tissue, synovial fluid, and vitreous humor. The Sepracoat solution coats tissues with a temporary protective layer and is completely resorbed from the abdomen within 5 days. ²⁸ After gynecologic surgery without a mesh, Sepracoat was found to lessen intra-abdominal adhesion formation. ²⁸ In the present study, Sepracoat did not significantly decrease the incidence of bowel or omental adhesions to the mesh.

Icodextrin is a biodegradable glucose polymer solution that has been registered for peritoneal dialysis. Although iso-osmolar, Icodextrin induces ultrafiltration through colloid osmosis. Through the attraction of fluid into the abdominal cavity, it is supposed to separate damaged surfaces while postsurgical regeneration takes place, thereby preventing formation of adhesions between surgical surfaces. Icodextrin is metabolized by amylase to oligosaccharides and remains in the human abdominal cavity for at least 3 to 4 days. ²⁹ In contrast to the present study, in which we found no effect of Icodextrin on adhesion formation, Verco et al. reported fewer adhesions after administration of Icodextrin in a uterine horn model in rabbits. ³⁰ In the rat, the intra-abdominal amylase concentration is higher than in the rabbit, which may lead to a shorter intraperitoneal residence time of Icodextrin in the rat.

Coated Meshes

Recently, coated meshes, with a protective layer on the visceral side of the mesh, have been introduced in surgery. The aim of the protective layer is to provide sufficient separation between the mesh and viscera while regeneration takes place without impeding tissue ingrowth of the mesh on the other side.

Sepramesh is composed of a polypropylene mesh that is coated with a bioresorbable membrane of hyaluronate and carboxymethylcellulose, which are bonded by polygalactide/polyglycolide. The antiadhesive membrane remains in place for up to 7 days ³¹ and is subsequently absorbed. As was shown in the present study, Sepramesh significantly reduced adhesion formation to the mesh after 7 days as well as after 30 days, when the membrane was completely absorbed. In addition, adhesion of viscera to the mesh was prevented after 7 days. After 30 days, the same trend was seen, although the difference was not statistically significant due to limited sample size.

In a rat and rabbit model, a bioresorbable membrane of hyaluronate and carboxymethylcellulose (Seprafilm) has been reported to diminish adhesion formation significantly. 15,16,18,32 However, this membrane is not applicable in laparoscopic incisional hernia repair because of technical difficulties with the introduction and positioning of the sticky membrane. The soluble form of Seprafilm (Sepracoat) would be easier to apply laparoscopically, but it did not reduce adhesions in the present study. A possible explanation for this discrepancy between the results of Sepracoat and Seprafilm is the difference in intra-abdominal lifetime. Sepracoat persists at its site of application for only approximately 24 hours, while Seprafilm remains in place for at least 7 days. ^28,31 Thus, intra-abdominal residence time might be an important factor and may have to exceed at least 7 days.

The Parietex composite mesh is a polyester mesh coated with an absorbable and hydrophilic film on the visceral side. The film is composed of a solution of oxidized bovine atelocollagen type I, polyethylene glycol, and glycerol. ³³ Within 3 weeks the film is completely resorbed and a new peritoneal covering is formed over the mesh. ³³ In the present study, the hydrophilic film provided significant protection against bowel adhesions after 7 days. The same trend was seen after 30 days, although the difference was not statistically significant due to limited sample size. Reduction of adhesions with the use of Parietex composite mesh was also found by Mutter et al. ³³ However, in the current study, Parietex composite mesh was more easily infected than the other meshes and showed a stronger inflammatory response. With infection and increased inflammatory reaction, concurrent increase of the surface of the mesh that was covered by adhesions was seen. A stronger inflammatory reaction with an increased incidence of infection and formation of enterocutaneous fistulas (16%) with the use of polyester mesh was also found in a clinical study by Leber et al. ¹¹

In conclusion, Sepramesh significantly reduced adhesion formation and prevented bowel adhesion to the mesh in the early postoperative period without interfering with wound healing and tissue incorporation of the mesh. Parietex composite mesh reduced bowel adhesions to the mesh as well but provoked a stronger inflammatory reaction in the current model. Addition of liquid physical barriers such as Sepracoat or Icodextrin did not prevent adhesion of omentum or bowel to a polypropylene mesh. Future clinical studies are indicated to assess the promising results of coated meshes.