Background: Anal fistula is by definition the communication between the rectum or anal canal with the perineal region, which may be epithelialized and has cryptoglandular origin in 90% of cases. There are a large number of techniques for successfully treating trans-sphincteric fistulas of 20-50%, including primary sphincteroplasty, but it is not clear whether the material used would influence the outcome. Aim: To analyze the efficacy of polydioxanone and polypropylene wire in primary post-fistulotomy sphincteroplasty in the treatment of trans-sphincteric fistulas in rats. Methods:Thirty Wistar rats had transfixation of the anal sphincter with steel wire, which remained for 30 days for the development of the anal fistula. After this period, it was removed and four groups were formed: A (control) without treatment; B (fistulotomy) submitted to such procedure and curettage only; C (polidioxanone) in which sphincteroplasty was performed after fistulotomy with polydioxanone wire; D (polypropylene) submitted to the same treatment as group C, but with polypropylene wire. After 30 days, euthanasia and removal of the specimens were performed for qualitative histopathological analysis, measurement of the area between the muscular cables edges and evaluation of the degree of local fibrosis. Results: There was persistence of the anal fistula in all animals of group A. There were no significant differences between groups B, C and D regarding the distance of the muscular cables (p=0.078) and the degree of fibrosis caused by the different treatments (p=0.373). Conclusions:There was no difference between polydioxanone and polypropylene wires in post-fistulotomy primary sphincteroplasty, and this technique was not superior to simple fistulotomy in relation to the distance of the muscular cables nor did it present differences in relation to the degree of local fibrosis.

Rationale  Fistulotomy followed by primary sphincteroplasty is one of the therapeutic options in transsphincteric fistulae; however, it was not known which suture would present a better result. Objective  To compare polypropylene and polyglactin sutures in primary sphincteroplasty in rats subjected to fistulotomy. Method  Thirty Wistar rats were subjected to peritoneal anesthesia with ketamine and xylazine, followed by transfixation of the anal sphincter with steel thread, which remained for 30 days to develop the anal fistula. After this period, the steel thread was removed and four groups were formed: A – Control ( n = 5), without treatment; B – Fistulotomy ( n = 5), performed fistulotomy only; C – Polypropylene ( n = 10), in which fistulotomy was performed followed by primary sphincteroplasty with polypropylene suture; D – Polyglactin ( n = 10), in which fistulotomy was performed followed by primary sphincteroplasty with polyglactin suture; after 30 days the animals were anesthetized again and submitted to euthanasia by deepening the anesthetic plane to remove the specimens, analyzing fistula closure, muscle fiber distance, and inflammatory process. Results  The fistula persisted in all animals of the control group and in none of the other groups; the distances between the muscle fibers were 1620 μm, 4665 μm, and 2520 μm, respectively in Groups B, C, and D ( p = 0.067); in relation to fibrosis, the means were 2.4, 2.8, and 3.6, respectively in Groups B, C, and D, showing greater fibrosis in the latter group ( p = 0.041). Conclusion  There was no persistence of the fistula in any of the treated animals; there was no difference in the distance between the muscle fibers between the groups subjected to primary sphincteroplasty with polypropylene or polyglactin, or between these groups and the one treated only by fistulotomy. There was greater fibrosis in animals treated with primary sphincteroplasty with polyglactin.

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