Tissue interposition flaps are frequently used to achieve better surgical outcomes for the repair of vesicovaginal fistulas (VVF). Research on the use of tissue interposition flaps in VVF repair is a broad area where a very wide range of natural and synthetic materials have been used in clinical studies that vary from case studies to randomized controlled trials. In this study, we systematically reviewed all synthetic and autologous interposition flaps used in VVF repair in terms of surgical outcomes and biomaterial properties.

We searched the literature using OVID Medline and PubMed databases for this study. The review included autologous and synthetic interposition flaps which are used for VVF repair. The inclusion criteria were as follows: 1- the patient was diagnosed as VVF; 2- tissue interposition flap used in at least one of the study groups; 3- studies with more than 10 patients; 4- objective and/or subject outcome measures were clearly defined. Study characteristics were recorded and data on the fistula size and location, number of patients, study groups, complexity and follow-up durations were extracted from each study independently by two authors (Table 1).

A total 23 articles that met the inclusion criteria were included in the review. Three of them were prospective randomized studies 2 were prospective and the rest were retrospective case series. In three of the six articles comparing the groups with and without interposition flaps, the success rates of cases using interposition flaps are higher than those without. 
Ten different types of autologous interposition flaps (Martius, omental, peritoneal, urachal, abdominis muscle, gracilis muscle, ileal segment, bladder wall, rotational bladder and singapore flaps) and seven different kinds of synthetic interposition flaps (Fibrin glue, cyanoarclic glue, small intestinal submucosa, acellular collagen matrix, oxidized cellulose, gelatin matrix and platelet rich plasma) have been used in VVF repair surgeries. Of these flaps, studies have met our inclusion criteria for seven autologous flaps and two synthetic flaps with 979 and 73 patients having received autologous and synthetic flaps, respectively.   The most commonly used autologous and synthetic interposition flaps were Martius Flap and the Fibrin glue, respectively. Surgical success rates have been reported between 60-100% for autologous flaps and 70-100% for synthetic flaps. Autologous flaps are commonly used in fistulas of 1-7.5 cm in size, while synthetic flaps are widely used in fistulas of 5 mm-2.5 cm in size. In the articles reviewed, the duration of follow-up after VVF repair ranged from 3 to 66 months. The fistula characteristics were highly variable with regards to their size, location, previous surgeries and other complicating factors among the studies. The aetiology of VVF was mainly gynecologic in the included studies and in 13 of the studies patients with radiation-induced fistulas were included. Standardized reporting of the postoperative complications were performed in only three of the studies.
With regards to synthetic interposition flaps, all were approved by the U.S. Food & Drug Administration (FDA) for human use as regulatory Class II medical devices and none of them were purpose designed for the intended use. The material characteristics of the synthetic interposition flaps are given in the table (Table 2).

The use of  tissue interposition flaps in VVF repair is common especially in complex and large fistulas. Autologous interposition flaps appear to be the standard of care at the moment and synthetic interposition flaps were investigated in prospective clinical trials in limited number of selected cases. Evidence levels of clinical studies evaluating the effectiveness of interposition flaps were overall low. The current methodological weakness in the surgical literature on the treatment of VVF causes a great deal of uncertainty about how evidence-based management of VVF treatment should be performed. Without eliminating these uncertainties, the results obtained from new techniques and new materials developed cannot be presented with strong evidence. Synthetic interposition flaps offer the advantage of being ready to use without any donor site morbidity. They can also potentially be more efficient however this needs to be investigated in prospective, controlled clinical studies with well defined fistula characteristics.

Autologous interposition flaps are commonly used in VVF repair with high success rates despite low level of clinical evidence. There have been trials on several synthetic flaps, none of which has gained widespread clinical use. Purpose designed synthetic novel materials can potentially improve clinical outcomes for patients with VVF.