Podiatry surgical complications

On Feb 5th a patient was seen at the hospital and had an amputation through metatarsal (28805) and form skin pedicle flap (15574) since then complications arose and she was readmitted on 2/25 and is requiring weekly debridements. It is my understanding the readmission (99221) can be billed with a 78 modifier showing complication, but what about the debridements? Apparently the surgical wound opened up and now is an ulcer. The doctor is using diagnoses non healing surgical wound since the 2/5 surgery. Please help!