The Efficacy of Human Placenta Mesenchymal Stem Cells Derived Exosomes Injection for Treatment of Complex Anal Fistula in Colorectal Surgery Department of Imam Khomeini Hospital Complex: A Non-randomized Clinical Trial.

The goal of this clinical trial is to learn if human placenta mesenchymal stem cells (MSC)-derived exosomes work to treat complex perianal fistula in adults without Crohn's disease. The safety of this treatment will also be learned. The main questions it aims to answer are:

• Does treatment with MSC-derived exosomes lower the number of fistula recurrences in participants?
• Is treatment with MSC-derived exosomes safe? We will compare treatment with MSC-derived exosomes to the routine treatment which is fistulotomy (surgery to close the fistula) alone to see if MSC-derived exosomes work better to treat complex fistula.

Participants will:

• Undergo fistulotomy plus MSC-derived exosome injections or fistulotomy alone.
• Visit the clinic the week after surgery and then every 4 weeks for checkups and tests