The first step consists of coring out the entire fistu-lous tract from the external to the internal opening (Fig. 8a). The intersphincteric space is curetted. The gap through the external and internal sphincters is closed by separate stitches of absorbable material starting from the anal lumen (Fig. 8c). The mucosa and anoderm, depending on the level of the tract, are excised around the internal opening. A flap of mucosa is undermined (Fig. 8b). The size of the flap must have a base which is twice the width of the apex, but the length should be as short as possible to reduce the risk of ischemia. The flap is sutured to the lower edge of the mucosa (Fig. 8d). The suture line must lie distal to the previous muscle closure. The external wound is left open. If the wound below the pectineal line cannot be totally closed, the flap is sutured to the muscles below the previous opening . No stoma is necessary. The external wound should be cleaned at least twice daily with saline and some disinfectant solution. This technique preserves a greater amount of sphincter than any other: it minimises scar formation, avoids anatomic deformity such as keyhole deformity and does not require any intestinal diversion. If a recurrence of the fistula occurs, the procedure can be repeated later. When the anorectal mucosa is minimally inflamed and the Crohn's disease is under control, with or without a reduced amount of steroids, success rates from 40-60% can be expected [70-72]. In our experience of 42 patients treated with advancing flap technique, 23 patients (54.7%) were free of fis tula 1 year after the procedure. Functional results confirm that this technique does not change the median maximal resting pressure nor the resting pressure profile of the anal canal because the external sphincter is preserved and no keyhole deformity is created . After severe prior inflammation, extensive sub-mucosal and even transmural fibrosis can make construction of an advancement flap difficult. In some complicated fistulae, the technique should not be the primary treatment used. The situation should be simplified by earlier surgery so that there is only a single tract remaining. Finally, a previously drained supral-evator fistula extending close to the rectal wall will not leave enough residual tissue to support an advancement flap. Using the flap technique in this situation would lead to leakage at the suture and a recurrence of the fistula.
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