If the necrotic areas are on the outside edge of a wound that is already open then I would use a debriding agent on those necrotic areas. Something like wound gel or nu gel or sorbsan. Use wet to dry with the gels if the wound is already dry only until the necrotic areas have been debrided, then d/c the gels. With the sorbsan, I have used this product on a stage 3 heel wd with great success. You just apply a thin layer of this soft fibrous dressing to the wound bed only, cover with dsd. Change daily at first to prevent infection. Good luck!