title: Effect of relaparotomy through previously integrated polypropylene and polytetrafluoroethylene experimental implants in the abdominal wall.
abstract: BACKGROUND
  The appearance of new pathologies affecting abdominal organs after implant of a prosthesis to repair an abdominal wall defect may necessitate reintervention. The aim of this study was to compare the behavior of two types of biomaterial widely used in clinical practice, polypropylene (PL) and polytetrafluoroethylene (ePTFE), after a second laparotomy involving the implant. The behavior, in terms of tensile resistance and integration with tissues, of intact prostheses was compared to that of prostheses subjected to opening and repair.
  
  
  METHODS
  A defect (7x5 cm) involving all tissue layers was created in the anterior abdominal wall of 24 male New Zealand rabbits. These defects were repaired with a reticular, macroporous PL mesh (Marlex, Bard Card., Madrid, Spain) or a laminar, micro/macroporous ePTFE prosthesis (Mycro Mesh, W.L. Gore, Flagstaff, AZ) of similar size to the defect. Four study groups were established: Intact PL/Intact ePTFE (n = 6 each): animals implanted with a PL or ePTFE prosthesis and sacrificed 90 days after implant; Repaired PL/Repaired ePTFE (n = 6 each): animals implanted with a PL or ePTFE prosthesis subjected to midlongitudinal relaparotomy through the center of the prosthesis 90 days postimplant, followed by repair with continuous polypropylene 4/0 suture. Animals in repaired groups were sacrificed 90 days after the second intervention. Specimens comprised of prosthesis and neoformed tissue were subjected to light and scanning electron microscopy. In addition, 2 cm-wide strips, consisting of the prosthesis and anchorage tissue, were subjected to biomechanical analysis using an Instron tensiometer (Instron, Canton, MA). The results obtained were statistically compared using the Mann-Whitney U-test.
  
  
  RESULTS
  The intact PL implants were fully infiltrated by dense, disorganized, well-vascularized scar tissue with fibers concentric to the mesh monofilaments. The appearance of the repaired PL prostheses was similar, with establishment of neoformed tissue in repaired areas of the prosthesis such that both cut edges of the prosthesis were joined together. In contrast, intact ePTFE prostheses were encapsulated by organized tissue with fibers running parallel to the surface of the biomaterial. Repaired ePTFE prostheses including sutured areas were similarly encapsulated. But the edges of the sutured middle area did not fuse. Tensile resistance values of intact and repaired PL prostheses were similar (intact, mean, 34.78 Newtons; repaired, mean, 34.74N, p>0.001). Tensile resistance values of intact ePTFE implants were significantly different to those of the repaired ePTFE prostheses (intact, mean, 22.64N; repaired, mean, 17.21N, p<0.001). Breakage of both types of PL specimen strips was restricted to recipient tissue while breakage of intact ePTFE specimens occurred in the areas of anchorage to the abdominal wall. Rupture of repaired ePTFE specimens took place in the sutured central areas of the prostheses.
  
  
  CONCLUSIONS
  We conclude that relaparotomy through an existing PL prosthesis previously integrated with the abdominal wall does not affect the tissue integration process or the tensile resistance of the implant. When the relaparotomy involves an ePTFE prosthesis, however, although the repair process itself is unaffected, significant loss in tensile strength is incurred. In addition, relaparotomy through both types of biomaterial is likely to result in the neoformation of adhesions in the areas of the prosthesis subjected to opening and repair but, in general, the number of adhesions formed in the presence of intact or repaired polypropylene implants was larger than that observed with the use of ePTFE.
authors.affiliation: Department of Morphological Sciences and Surgery, Faculty of Medicine, University of Alcalá de Henares, Madrid, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Bellón
authors.forename: L A
authors.initials: LA
authors.lastname: Contreras
authors.forename: J
authors.initials: J
authors.lastname: Buján
authors.forename: G
authors.initials: G
authors.lastname: Pascual
authors.forename: A
authors.initials: A
authors.lastname: Carrera-San Martín
mesh_terms: D000009:Abdominal Muscles / Q000601:surgery*; D000818:Animals; D001672:Biocompatible Materials; D002921:Cicatrix / Q000473:pathology; D020007:Implants, Experimental; D007813:Laparotomy; D008297:Male; D008855:Microscopy, Electron, Scanning; D011126:Polypropylenes; D011138:Polytetrafluoroethylene; D011475:Prosthesis Failure; D011817:Rabbits; D012086:Reoperation; D013526:Surgical Mesh; D013718:Tensile Strength; D000267:Tissue Adhesions / Q000473:pathology
chemical_list: D001672:Biocompatible Materials; D011126:Polypropylenes; D011138:Polytetrafluoroethylene