Fig. 1

a Pictures of the treated wound in the patient with annular avulsion and anal retraction in lithotomy position (the arrow shows the edge of the anus). b 14 days after surgery, 12 × 8 cm skin necrosis, prowl separation area approximately 85 × 65 cm, the purulent exudate in the space, and the original fixed anus shortened (the arrow shows skin necrosis). c The necrotic tissue was resected, fully revealing the wound, and the abscess cavity was washed. d Resecting partial subcutaneous fat, interrupted suture of the flap and perianal skin, anal formation, vacuum assisted closure (VAC) coverage of the wound surface (the arrow shows the anus). e: 24 days after surgery, incision with silk thread, anal retracted, wound infection present (the arrow shows the anus). f A piece of free full thickness skin after excision, suture fixed near the anal side, the anus and wound isolated, the anus was reshaped, and the wound covered with VAC (the arrow shows the anus). g 34 days after surgery, the clean wound surface, fresh granulation, the prowl separation closed, incision healing in the shaped anus. The wound blocked by skin grafting. h The wound covered with VAC. i 48 days after surgery, wound and perianal skin healed (the arrow shows the anus)