Interposition Layer in Fistula Repair (Dartos Flap)

If the suture line created when the channel is closed lines up with the skin's suture line, the two lines can open into each other during healing, letting urine reach the skin — in other words, a fistula forms.

• An interposition layer separates these two lines and places living, well-supplied tissue between them.

• The dartos flap — a thin, well-vascularized layer beneath the penile skin. The most commonly used option.
• Tunica vaginalis — a layer prepared from the covering of the testis; comes up when tissue is insufficient.
• Adjacent subcutaneous tissue — in limited repairs.

An interposition layer is not used only in fistula repair — it is also applied in the primary hypospadias repair, and it is the main technical precaution that reduces the chance of a fistula. It is worth asking, at the pre-operative consultation, "will you be using an interposition layer?"