Treatment of Lower Transsphincteric Perianal Fistula: Fistulotomy With Marsupialization vs Open Wound

This is a multi-center triple blinded randomized clinical trial in which we'll compare two techniques for the treatment of simple low transsphincteric perianal fistulas. 40 patients will undergo a fistulotomy with marsupialization and 40 patients will undergo a fistulotomy with open wound. There will be an inclussion visit in which personal information will be recorded and the consent will be signed. Randomization will be done after inclusion, following a balanced blocks model. Information of the surgery technic won't be available for the investigator. The patients will have a journal in which they'll write their postoperative symptoms. Follow up will be done at weeks 2, 4 and 6 by the main investigator of each center. Data will be based in clinical examination, patient's diary and medical records. Statistical analysis of the primary outcome will be based in a superiority analysis using the Mantel-Cox test, or in case needed, a multivariate Cox regression analysis. The secondary outcomes will be analyzed by comparing times, percentages, mean or median with parametric or non parametric tests as it corresponds.