This prospective pilot study includes 6 patients suffering from chronic anal fissure. All patients were previously treated with different local applications of glyceryl trinitrate or topical Xylocaine gel. Some patients took oral analgesics as a concomitant therapy for additional pain control. None of the patient received neither topical calcium channel blockers nor Botulinum toxin injection due to the unavailability.

The primary outcome measured is "time to complete cessation of anal pain". The secondary outcome includes the healing of chronic anal fissure defined as "time to complete epithelization".

The study was approved by the Ethics Committee of the First Surgical Clinic, Faculty of Medicine, and University of Belgrade. The study was performed in accordance with the Declaration of Helsinki and current Good Clinical Practices. All patients gave the written informed consent prior to the participation.

Physical examination and the detail medical history has been taken by an experienced colorectal surgeon. Pain assessment is quantified using the visual analog scale (VAS) before the treatment and during each postoperative outpatient visit. Bowel continence has been also assessed using Wexner fecal incontinence score prior to the treatment and during each postoperative outpatient visit. The liposuction procedure has been performed performed under the combination of local anesthesia and moderate sedation/general anesthesia. The mixture of 180 mL saline solution, 1mL Epinephrine (1:10,000) and 20 mL of 2% lidocaine is injected in the subcutaneous layer of the abdominal wall to allow the tumescence and to decrease the blood loss. The manual liposuction procedure has been carried out through two or three small incisions using Sforza harvester (Tulip® medical products, San Diego, USA). Approximately 150-200 mL of raw lipoaspirate is obtained from each patient. The harvest site is then covered with a pressure dressing for 10 days to reduce swelling and hematoma. The closed system PureGraft® 250mL (PureGraft®, Solana Beach, California, USA) has been used used to collect the specimen. The specimen is transferred within 15 min to the BelPrime Clinic laboratory where the Celution® 800/CRS system (Cytori Therapeutics, Inc. San Diego, California, USA) is applied to process the lipoaspirate in order to obtain ADRCs. The Celution® 800/CRS system is a closed automated medical device that helps to separate blood and fat. The system will then digests fat using the proprietary enzyme reagent Celase 835/CRS (Cytori Therapeutics, Inc. San Diego, California, USA) to release the stromal vascular fraction (SVF). SVF is subsequently concentrated by a short centrifugation and then automated wash cycles to obtain the ADRC fraction. This 90 to 120-minute process provides approximately 5mL of pellet. A few drops of the obtained pellet were immediately used for cell counting (ChemoMetec A/S DK-3450, Allerod, Denmark).

The second procedure has been performed in lithotomy position. Intravenous prophylactic antibiotic (1gm Metronidazol) are administered. After the careful and gentle anal examination, anal fissure is first curetted using a small size curette. The pellet is divided into two parts. The first 2mL of the pellet is mixed with 8mL of the lipid part of the lipoaspirate purified by Puregraft® 50 system. This solution (10mL) is injected subcutaneously into the edge of the fissure using the criss-cross lattice technique by Tulip® 1,2 mm injector. The rest of the pellet, (approximately 2-5mL), is infiltrated directly into the fissure base (internal anal sphincter) using a 20G needle. No laxatives or stool softener is prescribed. Patients have been discharged from the hospital a few hours after the procedure.

Patients are followed up weekly by telephone interview during the first 2 months, then monthly up to 12 months after the procedure. The outpatient visits are scheduled monthly until 9 months to ensure the healing of anal fissure. Visual analogue scale (VAS) score and Wexner fecal incontinence score \[31\] are also recorded.