Diseño de nuevos métodos de cierre de la pared abdominal empleando materiales protésicos. Su importancia en la mejora de la resistencia mecánica a nivel de la línea media

Abstract

The midline laparotomy is one of the most common surgical techniques used to access the abdomen. Despite the benefits offered by the transverse opening (less pain, improved respiratory tolerance, etc.), the midline laparotomy still has several precise indications in digestive surgery, emergency surgery and vascular surgery. It can be quickly undertaken, can be extended proximally or distally depending on the specific needs of the situation and thus provides a broad surgical field in which to work. The midline procedure also provokes less bleeding than the transverse approach. Opening for a midline laparotomy is conducted along the linea alba. Although affected by anatomical variations, this can be a weak zone of the anterior abdominal wall. The incidence of hernia following laparotomy closure continues to be fairly high (2-16/20%), especially after a midline procedure. Thus, there is a need for a method of strengthening laparotomy closures especially in the higher risk procedures (midline or in obese patients) or in patients with compromised scarring (those with diabetes, jaundice, immunosuppression, malnutrition, cancer, etc.). This need prompts the design of improvements that rather than insisting on essentially technical variables (e.g., running vs interrupted suture; closure en masse vs by planes; absorbable vs nonabsorbable sutures), constitute new concepts within the context of the tissue wound-repair process. In this study, we demonstrate the improved scarring and mechanical strength of the abdominal wall achieved by incorporating a new polypropylene biomaterial between the cut edges of the incision made along the linea alba. The objective was to create a new pseudotendinous zone with sufficient scar tissue both in a vertical and horizontal plane to add tensile strength to the normal strength achieved by conventional closure by suture. Two prosthetic meshes were designed: a prosthesis V-shaped in cross-section with two sides and a rounded vertex and a T-shaped prosthesis with a vertical and a horizontal surface at right angles to each other. The horizontal arm of the T was coated with an expanded polytetrafluoroethylene (ePTFE) barrier sutured to it using CV4 thread of the same material. The experimental animal used was the New Zealand White rabbit of average weight 2500 g. The implants were performed along the linea alba after making a 7 cm-long laparotomy incision. The mesh strips were stitched to the facial edges of the incision using polypropylene 3/0 suture. Closures were always conducted by the same surgeon according to the Jenkins 4:1 suture thread:wound ratio. The following study groups were established: Control group – non-operated animals; Group I – animals with a simple polypropylene suture midline laparotomy closure; Group II – animals with a midline laparotomy closure including a V-mesh; and Group III - animals with a midline laparotomy closure including a T-mesh. The animals were sacrificed at 3 weeks, 6 weeks or 6 months, at which time specimens of host tissue/mesh were obtained for light microscopy, scanning electron microscopy and immunohistochemical staining for macrophages. The tensile strength of the tissue specimens was measured in an INSTRON tensiometer. Data were compared using the Mann Whitney U-test. Three weeks after laparotomy closure, the V-mesh in the group II animals appeared perfectly integrated within a host tissue rich in collagen and showing marked angiogenesis. In some animals, peritoneal adhesions to the vertex zone of the V were observed. Findings at 6 weeks were similar although more neoformed scar tissue and a greater extent of fibrosis were noted. At six months, the implant was filled with a more vascularized, compacted scar tissue. In group III, we observed the presence of scar tissue occupying the middle zone of the Tmesh at 3 weeks. The peritoneal-facing mesh surface was comprised of a typical mesothelium lining the ePTFE. Six months after implant, scar tissue appeared compacted and the peritoneal mesh surface was perfectly mesothelialized. Immunolabelled macrophages decreased in numbers over time with higher counts obtained for the T-mesh implants. In the biomechanical study, tensile strengths similar to the control unopened linea alba were recorded for the closures including a V- or T-mesh. Statistically significant differences were detected with respect to the simple running polypropylene suture. From three to six weeks, strength gains were recorded for both the V- and T-meshes. At 6 months, tensile strengths approached (V-mesh) or even surpassed (T-mesh) the values recorded for the intact linea alba, although differences were not significant. Our findings indicate that a midline laparotomy closure reinforced with a prosthetic material gives rise to similar tensile strengths to those recorded for the control, or intact, linea alba.