Use of indigenous knitted nylon mesh to repair large abdominal defects--an experimental study.
Surgeons may be called upon to repair giant incisional hernias and massive full thickness defects in the abdominal watt occuring due to extensive infections and excision of abdominal tumours, trauma, gas gangrene or electric burns. In such situations, it is imperative to use myocutaneous flaps or extrinsic materials like- Synthetic meshes,  to avoid closure under tension. Myocutaneous flaps require special facility and training. Mesh plasty. however, is a simple procedure even in the hands of a general surgeon.
A study was carried out in ten adult mongrel dogs to compare the technique of monolayer nylon interrupted closure of a standard laparotomy incision with an onlay nylon mesh (indigenously knitted) plasty to bridge a large abdominal defect. The factors evaluated were: (i) the tensile, strength of the wound, (ii) the incidence of local complications such as sinuses abscesses, infections, etc., (iii) incisional hernia formation, (iv) peritoneal regeneration and adhesions and (v) histopathology of healing margins.
Ten adult mongrel dogs weighing on an average 20 kg were used for the study. A midline 10 cm long, laparotomy was performed under pentothal-scoline anaesthesia. The incision was then closed using too. interrupted nylon sutures by the monolayer technique. The sutures were placed 1 cm apart taking 1 cm thick bites of the abdominal wall. The dogs were examined every week for the presence of wound weakness, burst abdomen and wound infection. Six weeks later, after dissecting the overlying skin from the underlying muscles, the entire mid-line incision with 3 cm abdominal wall including the peritoneum on either side was excised en block under general anaesthesia. After thorough hemostasis, the abdominal wall defect measuring 10 cm x 6 cm in size was bridged by an onlay graft of an indigenous, knitted nylon mesh. The mesh was sutured, without crimping, to the edges of the defect using interrupted No. 1 nylon sutures taking, full thickness 2 cm deep bites- at 1 cm interval [Fig. 1]. The knots of these sutures were turned downwards and buried into the muscles. Moderate tension was maintained on the mesh to prevent bulging. The peritoneum was not closed on the under surface of the mesh. The skin over the mesh was closed with interrupted linen sutures. Chloramphenicol was given IM/orally to each dog for 10 days after each experiment. The dogs were evaluated every week as before and were re-explored six weeks later. The entire mesh-bearing area along with a 4 cm block of adjacent abdominal wall was removed with the, underlying peritoneum. The (loge were: sacrificed using intravenous potassium chloride.
The following observations were made:
I. Local changes:
(1) infection, abscess,
(2) sinus formation,
(3) wound disruption,
(4) incisional hernia.
II. Intraperitoneal changes:
(1) healing of peritoneum on the under surface of the incision and mesh,
(2) adhesions: type and extent (in per cent of the entire length) to the incision and mesh.
III. Tensile strength- of incision at the mesh abdominal wall interface:
An indigenously developed tensiometer was used to measure the tensile strength16 (expressed as kg/cm). The break at the maximal tensile strength invariably occurred at the mesh-abdominal wall interface.
IV. Histopathology of regenerated peritoneum. and the mesh-abdominal wall interface.
There was no pre- or post-operative mortality.
[Table - 1] outlines the morbidity encountered during the study.
The difference in the mean tensile strength in both groups was statistically not significant (using Wilcoxan-Rank Sum test p > 0.05). As seen in [Fig. 2], there is a considerable overlap in the tensile strength figures in both groups.
The review of histopathology sections stained with hematoxylin-eosin and Masson stain showed a completely normal peritoneal regeneration in both the groups. There was an almost equal component of inflammatory cells and fibroblasts in both the groups. The depth of inflammatory and fibrous reaction in the mesh plasty group was marginally more than that seen in the interrupted nylon monolayer closure group. although there was no gross penetration of the muscle layer by the inflammatory reaction. In only one case was there a mild foreign body reaction but clinically that case showed no rejection of the mesh.
Most of the surgeons have had occasions to sweat over a large incisional hernia it an obese patient with attenuated muscles and underlying hostile factors like straining, poor healing, distension and infection.
The standard anatomical closure of such defects is performed under tension; the compression of intra-abdominal content occasionally produces cardiac and pulmonary embarrassment. In some cases, the gap is too large to be bridged by mere anatomical apposition of wound edges.
It is these cases that need to be strengthened and supported with extraneous material. Various authors have preferred either mersilene, marlex,  or vikryl meshes.
We have used an indigenous, knitted nylon mesh as an onlay graft to bridge the defect. There was no compromise in the final strength of the repair achieved. The tensile strengths of monolayer nylon closure and full thickness mesh plasty replacement were statistically not different [Fig. 2]. In both groups there was no incidence of incisional hernia. There was no incidence of rupture of the mesh even at maximum tensile strength. The interface between the mesh and abdominal wall was invariably the site of disruption of the wound at the maximal tensile strength. This has been also observed in an earlier study.
The presence of inflammatory cells and fibroblasts at the healing interface represents two different evolutionary steps of the cicatrization process. The former could be considered to reflect the tolerance of the host to foreign material and the latter, the histological feature corresponding to the mechanical resistance of the repaired wound. The depth of inflammatory and fibrous reaction in mesh repair group marginally exceeded that in the monolayer nylon closure group. However, the regeneration of the peritoneum was identical in both groups. This is in conformity with earlier observations., 
The defect in the peritoneum underlying the mesh heals by the regeneration of the peritoneum in situ and not from the cut edges of the defect, a fact in conformity with earlier studies.,  The regenerated peritoneum has no significantly higher incidence of adhesions as compared to the sutured peritoneum [Table - 1]. In this study, the nature of adhesions was flimsy and involved 55-75% of the incision length in both the groups.
Infection is not a contraindication to the use of the mesh. In fact, in cases of peritonitis it has a therapeutic value and its porosity permits the passage of intraperitoneal fluids (ascites, effusions) to the outside.
The mesh we used was made of knitted nylon. It was non-toxic, durable, strong and resistant to fatigue and fragmentation. It produced enough tissue reaction to generate a strong fibrous healing of the defect. Studies by several authors emphasize this as the crux of the tensile strength of the closure., 
The infections and sinuses related to the, stitches have been known to chiefly occur due to the use of cotton/silk/linen etc. We minimized this complication by using mono-filament No. 1 nylon sutures.
Interrupted sutures were used for multiple point non-tension fixation. This helps by dividing the stress evenly over the mesh and reducing crimping. A stitch-related sinus can be removed easily without disturbing the strength of the closure as a whole. It also prevents the gathering and bulging of the mesh.
The mesh lies exposed on the muscle surface and underlies the subcutaneous and skin surface. The knots are reversed and embedded into the surrounding tissue. This helps to minimize the local discomfort. The advantage of the onlay technique is the ease of implanting the mesh, the easy removal of infected stitches and curled up corners and in the eventuality of the whole mesh being shrounded in infection in an odd case, the entire mesh can be removed without difficulty. The only disadvantage is the possibility of local discomfort and the erosion of mesh through subcutaneous tissue and skin, which was not seen in the present study.
We are grateful to the Dean, Seth G. S. Medical College and K.E.M. Hospital. Parel, Bombay 400 012, for allowing us the use of the experimental laboratory and to the staff. of the laboratory-Mr. S. S. Jethegaokar, Mr. M.S. Kule and others for their kind co-operation and also to the VIFOR Laboratory, Bombay. for supplying the nylon mesh.