+ In 10 cases of flap necrosis less than 50%: 6/11 patients had superficial necrosis of the epidermis at the top of the flap and the edge of the flap after self-healing dressing change; 4/11 cases of necrosis of the entire epidermis at the top of the flap, removed, bandaged and skin grafted in half; + 1 case of flap necrosis over 50%, the necrotic flap is located in the epidermis along the flap axis in the middle and second half of the flap.