Advancement flap technique for a rare complex anal fistula with synovial cyst at the ischial tuberosity.

"Declarations Conflict of interestAll authors have nothing to disclose. Ethical approvalAll procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consentInformed consent was obtained from the participant included in the study. Consent for publicationAll authors agree to publish. Patient signed informed consent and was willing to submit the information. Conflict of interest All authors have nothing to disclose."

"Funding Funded by National Natural Science Foundation of China (82174373); Xinglin scholar (tracking plan) of Shanghai University of traditional Chinese medicine; General project of Shanghai Municipal Health Commission (202040161)."