Effect of relaparotomy through previously integrated polypropylene and polytetrafluoroethylene experimental implants in the abdominal wall

Background: The appearance of new pathologies affecting abdominal organs af ter implant of a prosthesis to repair an abdominal wall defect may necessit ate reintervention. The aim of this study was to compare the behavior of tw o types of biomaterial widely used in clinical practice, polypropylene (PL) and polytetrafluoroethylene (ePTFE), after a second laparotomy involving t he implant, The behavior, in terms of tensile resistance and integration wi th tissues, of intact prostheses was compared to that of prostheses subject ed to opening and repair. Methods: A defect (7 x 5 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 P L or ePTFE prosthesis and sacrificed 90 days after implant; Repaired PL/Rep aired ePTFE (n=6 each): animals implanted with a PL or ePTFE prosthesis sub jected 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,disorganize d, well-vascularized scar tissue with fibers concentric to the mesh monofil aments. The appearance of the repaired FL prostheses was similar, with esta blishment 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 incl uding sutured areas were similarly encapsulated. But the edges of the sutur ed middle area did not fuse. Tensile resistance values of intact and repair ed PL prostheses were similar (intact, mean, 34.78 Newtons; repaired, mean, 34.74N, p > 0.001). Tensile resistance values of intact ePTFE implants wer e 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 prosthesi s previously integrated with the abdominal wall does not affect the tissue integration process or the tensile resistance of the implant. When the rela parotomy 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 resu lt in the neoformation of adhesions in the areas of the prosthesis subjecte d to opening and repair but, in general, the number of adhesions formed in the presence of intact or repaired polypropylene implants was larger than t hat observed with the use of ePTFE. (J Am Coll Surg 1999;188:466-472. (C) 1 999 by the American College of Surgeons).