The present invention relates to a medical device for the treatment of anal fistulas, constituted by a single element having the shape of a prism. The prism, has a particular geometric shape, sharp edges for its entire length. Said device is made of biomaterial and is characterized by having full thickness (solid body) so as not to be collapsible. This ensures primary stability and intimate contact with the walls of the fistula, These are the biomechanical conditions necessary for the integration of the device in diseased tissue. The device can also be characterized by the fact of having notches in its full thickness, safeguarding the body of the same. Their function is anti-extrusion, remaining closed during insertion in the fistula and opening if under any pressure to prevent extrusion. Solid body/full thickness alternative geometric shapes have been proposed that are all characterized by the presence of sharp edges, and the full thickness of the anti extrusion notches