Comparative Evaluation of Adhesions to Intraperitoneally Placed Fixation Materials: A Laparoscopic Study in Rats

Abstract

After laparoscopic ventral hernia repair, the nature of the adhesions to fixation materials or to mesh had not been clarified. We examined adhesion formation specific to the fixation material in rats. We designed an experimental laparoscopy setup, and placed four intraperitoneal fixation materials on the peritoneum of rats without a mesh graft. Another group of researchers documented the incidence and intensity of postoperative adhesion formation. The adhesion scores for the nickel-titanium anchor were significantly greater than those for polylactic acid (p = 0.004), a titanium tacker (p < 0.0001), and fibrin glue (p < 0.0001). No adhesions occurred in the fibrin glue group. Fibrin glue is the preferred fixation material because it produced no postoperative adhesions. The nickel-titanium anchor produced heavy adhesions but may be applicable for recurrent hernia cases and in patients with thin abdominal walls.

Introduction

Laparoscopic ventral hernia repair (LVHR) has become a standard method for repair of abdominal wall hernias [1–3]. In general, the technique consists of a reduction in the hernia contents, transabdominal insertion of an appropriate size and type of mesh, opening of the mesh intraperitoneally, and its fixation over the hernia defect on the posterior surface of the anterior abdominal wall [4–7]. As in open surgery, the most important complication of LVHR is visceral organ adhesions to the intraperitoneally placed prosthetic mesh graft. Foreign material, ischemic or avascular tissue, and factors that decrease peritoneal plasminogen activity cause intra-abdominal adhesions [6, 8]. Most adhesions after LVHR are between the intra-abdominal viscera and the prosthetic mesh graft but vary due to the nature of the graft itself [9–11]. In clinical aspects, intraabdominal adhesions may cause mechanical intestinal obstruction, intestinal fistula, early or late postoperative pain. So, the clinical research in this era should follow the experimental studies.

In fact, some recent data suggest that some of these adhesions are directly on the fixation materials rather than on the prosthesis [7, 11, 12]. However, whether these adhesions were due solely to the fixation materials or the mesh, and whether the fixation material caused a combined effect on adhesion formation has not been clarified.

In this study in rats, we examined the presence of adhesion formation specific to the fixation material itself. With this purpose in mind, we designed an experimental laparoscopy set-up, and placed four different intraperitoneal fixation materials directly on to the anterior peritoneum of four different groups of rats without using any mesh graft. Another group of researchers, blinded to the materials used, documented the incidence and intensity of the adhesion formation on these four fixation materials.

Materials and Methods

After receiving approval from the Animal Ethics Council, we conducted this study on 45 adult male Sprague–Dawley rats weighing an average of 210 g (ranging 190–230 g), which were fed with standard rat chow and water ad libitum.

Preparation

We randomly separated the rats into five groups, each containing nine rats, and a standard laparoscopic procedure was applied to the remaining rats. We induced anesthesia with an intramuscular injection of ketamine (20 mg/kg), and placed the rats in a supine position on the operating table. The skin was shaved and prepped with a povidone–iodine solution, and the procedure was performed under sterile conditions.

Surgical Technique

An 18-gauge needle was used as an insuflator. It was introduced into the peritoneal cavity from the right lower quadrant of the abdomen and connected to a stop-cock and a 50-mL injector. The intra-abdominal pressure was set to 6–8 mmHg on room air. Two 5-mm trocars were introduced into the abdomen from the suprapubic region. A laparoscope was introduced through one trocar and the fixation material was applied through the other trocar on the right and left side of the peritoneal surface under laparoscopic vision. The skin on the application site was hung with a grasper so as not to be perforated by any of the fixator. In the control group, we performed only laparoscopy and did not apply any fixation material. The four fixation materials were polylactic acid (PLA-Pariefix, Sofradim, Villefranche sur Saone, France), titanium tacker (TIT-Endotack, Autosuture, Mansfield, MA, USA), a nickel–titanium anchor (NTA-Endoanchor, Ethicon, Johnson and Johnson, New Brunswick, NJ, USA), and fibrin glue (FIG-Tisseel, Baxter, Deerfield, IL, USA).

Evaluation of Adhesions

Fifteen days after the operation, the abdominal walls of the rats were opened with a U-shaped incision to check the visceral adhesions to the fixation materials on both sides. Adhesions involved the omentum, small bowel loops, and the inferior margin of the liver. We defined the presence and severity of adhesions according to the Mazuji’s and Fadhli’s Adhesion Scoring System [13] (Table 1). Each adhesion was graded from 0 to 4; 0, no adhesions; 1, mild; 2, moderate; 3, dense; and 4, very dense adhesions (Table 2). For the practical evaluation, we further classified grade 1 and 2 adhesions as mild and grade 3 and 4 adhesions as heavy (Fig. 1). The mean adhesion score in each group was obtained by dividing the sum of the scores by the number of rats. Mean adhesion scores between 0.1 and 2.0 represented mild adhesions, while scores between 2.1 and 4.0 represented heavy adhesions (Fig. 2). We repaired the abdominal walls of the rats and did not sacrifice any of the rats.

Table 1.

Adhesion Scoring System (Mazuji and Fahdli (13))

Types of adhesions	Score
No adhesions	0
Filmy adhesions, easily taken manually	1
Moderately dense adhesions, taken manually without much force	2
Dense adhesions broken by scissor easily	3
Very dense homogenous adhesions, difficult separation by scissors	4

Table 2.

Distribution of adhesions to four different fixation materials

Adhesion scores	PLA		TIT		NTA		FIG
	Right	Left	Right	Left	Right	Left	Right	Left
0	5	5	6	6	1	1	9	9
1	1	1	2	1	-	-	-	-
2	1	1	-	1	2	-	-	-
3	2	1	-	-	5	5	-	-
4	-	1	-	-	-	2	-	-

Fig. 1.

The percentages of mild (grade 1 and 2) and heavy (grade 3 and 4) adhesions to four different fixation materials. (PLA: 22.2% for mild, 22.2% for heavy adhesions; TIT: 25% for mild, 0% for heavy adhesions; NTA: 12.5% for mild, 75% for heavy adhesions; FIG: 0% for mild, 0% for heavy adhesions)

Fig. 2.

The mean adhesion scores of the four fixation materials. (The 0 is for no adhesion. Any score from 0.1 to 2.0 represents mild adhesions, while 2.1 to 4.0 means heavy adhesions)

Statistical Analysis

The differences between the groups were analyzed using a Kruskal–Wallis nonparametric analysis of variance. Comparisons of the groups were made using the Mann–Whitney U-test with a Bonferroni correction. A p < 0.01 was considered statistically significant.

Results

One rat was excluded from the NTA group due to an application failure of the fixation material, and one rat in the TIT group was discarded due to its early postoperative death.

No adhesions occurred in the control group. The rates of mild adhesions were 22.2% in the PLA group (Fig. 3), 25% in the TIT group (Fig. 4), 12.5% in the NTA group (Fig. 5), and 0% in the FIG group (Figs. 1 and 6). The rates of heavy adhesions were 22.2% in the PLA group, 0% in the TIT group, 75% in the NTA group (Fig. 5), and 0% in the FIG group (Fig. 1). The numbers of adhesions related to the adhesion scores for each fixation material are shown in Table 2. The mean adhesion scores were 1.0 for the PLA, 0.2 for the TIT, 2.1 for the NTA, and 0.0 for the FIG group (Table 3, Fig. 2).

Fig. 3.

Heavy adhesions to the Polylactic Acid Fixator (PLA)

Fig. 4.

Mild adhesions to the Titanium Tacker (TIT)

Fig. 5.

Adhesions to the Nickel-Titanium Anchor (NTA), A, B – Heavy adhesions, C – Mild adhesion

Fig. 6.

No adhesions to the Fibrin Glue (FIG)

Table 3.

The mean adhesion scores of the four fixation materials

	Mean+/- SD	Median (min,max)
PLA	1.06+/- 1.39	0.00 (0.4)
TIT	0.31+/- 0.60	0.00 (0.2)
NTA	2.63+/- 1.15	3 (0.4)
FIG	0+/- 0	0 (0.0)

No significant differences were observed between the PLA and TIT groups (p = 0.198), between the PLA and FIG groups (p = 0.022 with Bonferroni correction), or between the TIT and FIG groups (p = 0.026 with Bonferroni correction).

A significant difference was detected between the PLA and NTA groups (p = 0.004), between the TIT and NTA groups (p < 0.0001), and between the FIG and NTA groups (p < 0.0001).

Discussion

Fixation is very important in the prevention of hernia recurrence. Fixation of the mesh can be done by various types of sutures and/or a spectrum of fixation devices. The application of these fixation materials during LVHR is easy, and reduces the operation time considerably [11, 12]. However the fixation materials may form visceral adhesions even if no prosthetic mesh graft is in the abdomen. Many cases of staples left inadvertently in the abdomen have been noted for a long time, causing severe abdominal adhesions [7, 9, 11, 14]. While secure fixation is a desired property of the fixation material, adhesions are not [9]. Tacks were known to cause fewer adhesions than the transfixion sutures [10]. The hyaluronic acid/carboxymethylcellulose covering of the mesh grafts by migrating over the metal tacks or remesothelialization over the foreign body, prevented adhesion formation to the tacks [10].

The operative trauma on the peritoneum when combined with the implantation of a foreign body increases the risk of adhesions. Dense adhesions followed by fistula formation have continuously reported with an intra-abdominally applied polypropylene mesh graft [3, 5]. To avoid adhesions, Attwood et al. recommended preperitoneal placement of the mesh graft with the remaining unbreached peritoneum [15]. The cause of adhesions may be ischemia and inflammation of the peritoneum. Increased numbers of fixators, such as staples, have resulted in more trauma and devascularization [3, 6]. Foreign bodies are well recognized causes for intraperitoneal adhesions [11]. The foreign body reaction is directly correlated with the amount of foreign material and influences adhesive potential of the peritoneum [5]. Inflammation depresses peritoneal fibrinolytic activity. The ischemia caused by the application of a fixator can increase traumatic adhesion formation, and the rotating activity of a specific fixator while penetrating the tissue causes greater trauma. For example, dense adhesions between the small bowel loops on the side with spiral tacks were identified especially stronger on the 30th and 90th postoperative days compared to sutures [11].

In our study, 10 out of 18 rats (55.5%) in the PLA group had no adhesions (Table 2). The other half of the PLA group produced adhesions. The heavy adhesions (score 3, 4) in 22.2% (Figs. 1 and 3) of the rats in the PLA group indicates that PLA may induce adhesions and related complications especially when an increased risk for adhesions exists as in repeated surgical procedures. Increased foreign body and inflammatory reactions during the PLA absorption process may cause dense adhesions. The mesh grafts covered with polylactic acid were found to have less adhesions [14, 16, 17]. However, Duffy et al. reported that absorbable polylactic acid and metal tacks resulted in equivalent adhesion formation [18].

In the TIT group, there were no adhesions in 75% of the rats. The remaining 25% of the adhesions were mild (Fig. 1), a result confirming less adhesive potential than that of PLA. Also, no heavy adhesions occurred (score 3 or 4) (Fig. 4). Which titanium property might cause an adhesion or whether any technical reason exists for the adhesion remains unclear. McGinty et al. reported that titanium tacks produced adhesions [7]. Le Blanc determined that fixators with smooth metallic surfaces, such as titanium, produced fewer adhesions [9]. When the titanium tack and the mesh are used together, few titanium helical fasteners were backing out of the mesh on gross examination. This resulted in less than complete penetration of the tack into the abdominal wall and increased exposure of the metal to the viscera [9], which may have caused the adhesions to the titanium tacker.

The adhesion scores were significantly lower in the PLA and titanium tacker groups than in the NTA group. The increase in the adhesion score for the nickel–titanium anchor may be related to technical issues. Also, Joels et al. reported that the incidence and tenacity of adhesions appeared to be greater with nitinol anchors than with polypropylene, polyglactin 910, or titanium spiral tacks [2], which may be related to the large intra-abdominal profile of nitinol anchors. A portion of the nitinol anchor extends a few millimeters into the abdomen, making it more likely to contact the omentum and intra-abdominal viscera. The abdominal walls of rats are thinner than those of humans, so the extension of the nitinol anchor may be shorter in the abdominal cavity of humans, resulting in fewer adhesions. Additionally, the penetration depth of the fixation material may be related with the degree of adhesion. A histological assessment showing fibrous reactions, foreign body reaction, and peritonealization may be useful to define these adhesive properties. In contrast, 75% of the adhesions to the NTA were scored as 3 or 4 (heavy adhesions) (Figs. 1 and 5). These heavy adhesions are a significant factor for postoperative morbidity. The added nickel to the anchor or the technical and morphological specifications of the anchor might have caused the severe adhesions. The adhesion capacity to fibroblasts or peritoneal cells at the cellular level may be identifiable in in vitro and in vivo experimental studies, especially for nickel.

In our study, the left side of the abdomen had predominantly tack adhesions like in Le Blanc’s study [9], which may have been due to the pressure applied by the animal on that side of the abdomen.

No adhesions occurred in the FIG group and no signs of fibrin glue were seen on the peritoneal surface during the second operation (Figs. 2 and 6). Fibrin glue, without any prosthetic material, produced no adhesions, so it was by far the best fixator regarding the prevention of adhesion formation; however, it was not apparent on the peritoneum 15 days after the application and was probably absorbed during this period. Fibrin glue contains fibrinogen, aprotinin (a protease inhibitor), thrombin, and CaCl₂. The fibrin sealant prepared from the Tisseel kit without aprotinin has the ability to reduce the extracellular matrix and transforming growth factor-beta 1 m-RNA levels, especially from adhesion fibroblasts, which may indicate a role in the reduction of postoperative adhesion formation. Tisseel may modulate human peritoneal mesothelial cells, normal peritoneal fibroblasts, and adhesion fibroblast functions [19]. Fibrin sealant, with or without aprotinin, affects the healing process by altering components of the plasminogen activator system, which may be of benefit for reducing postoperative adhesions [20]. The fibrin glue fixation of the mesh was strong enough to prevent migration of the mesh in experimental studies, so it might be the ideal fixation material.

As the implant material disappears, the adhesion may also disappear [5]. As seen in the fibrin glue group, the absorbable fixation material had few or no adhesions within 15 days postoperatively. Absorbable coverage of the fixator may prevent the formation of adhesions to the nonabsorbable fixators [8]. Schulze et al. showed that collagen sealant (a bioabsorbable material containing type-1 collagen) prevented the migration of Parietex composite mesh during an 8-week period when it was used as a fixator [21]. The signs of inflammation in the surrounding tissue, adhesions around the mesh, and strength of adhesion separation were reduced with absorbable coverage of the fixators [21, 22].

Conclusion

We prefer fibrin glue as a fixation material for laparoscopic hernia repair because it produces no postoperative adhesions. However, its fixation strength should be examined among different prosthetic mesh grafts. Nickel–titanium anchors produced heavy adhesions and may be used carefully in recurrent hernia cases and in patients with thin abdominal walls. Further experimental studies defining the adhesions produced after 2 weeks are necessary to determine the long-term results.