Is the Use of Blood Platelets Effective in the Treatment of Difficult Fistulas Related to the Anal Sphincter?

Rationale: Closure of the internal opening is the most accepted standard procedure in the treatment of peri-anal fistulas. The mucosal advancement flap is considered as golden standard. In one out of the three patients mucosal flap repair fails. Possible causal factors are incomplete clearance of pus and debris, incomplete closure of the internal opening, inappropriate host response in patients with risk factors like smoking or diabetes. Platelet derived growth factors may facilitate closure of the internal opening, especially in patients with impaired wound healing. Objective: The use of autologous platelet rich plasma (PRP) as an adjunct to the staged mucosal advancement flap to achieve a better closure rate of complex peri-anal fistula's. Study design: Randomized, multicenter trial. Study population: Patients with complex cryptoglandular peri-anal fistula's. Intervention: Injection of PRP in the curretted fistula track under the mucosal flap. Main study parameters/endpoints: * Recurrence rate * Post-operative pain * Continence * Quality of life. Nature and extent of the burden and risks associated with participation, group relatedness: Because autologous blood is used, no extra risk are expected.