1. Clinical data General data There were 16 cases in this group, 12 males and 4 females. The age ranged from 19 to 49 years. Causes of injury: 8 cases of cutting injury, 5 cases of avulsion injury, 3 cases of rolling injury. Injury site: 1 case of forearm, 1 case of palmar dorsum, 1 case of heel, 1 case of nose, and 12 cases of fingers. Among them, there were 7 cases of skin and fascia defects, 4 cases of muscle (tendon) and skin defects, 2 cases of (soft) bone and skin defects, and 3 cases of tendon, bone and skin defects. The defect area was 1.6cm×1.2cm～20cm×6.5cm. Surgical methods: (1) Thorough debridement: The disconnected tissue and the affected area were carefully debrided to remove the lifeless tissue. If necessary, microscopic debridement should be performed. Look for healthy arteries and veins to ensure their suturability. (2) Repair of severed bone, muscle, tendon, and nerve tissues: the fracture is fixed by restoring the fracture with kerchief stitches, the muscle and tendon tissues are closed with muscle sutures, and the severed nerve is closed with “9-0” silk sutures under the microscope. (3) Reconstruction of blood circulation: ① For arteries existing in the severed body, suturing with “9-0” to “12-0” silk sutures under the microscope according to the caliber of the vessel and the artery in the affected area. If necessary, vascular transfer and vascular bridging methods can be used. The number of venous sutures is determined by the size of the dissected tissue and the specific situation during surgery. If the tissue volume is small, usually 1 to 2 sutures are closed; if the tissue volume is large, 3 to 4 sutures are closed, and sutures are needed for those with accompanying deep veins. ②For the arteries that do not exist in the severed body, arteriovenous bridging is taken for replantation. If the amount of tissue is small and arteriovenous bridging is difficult, as many sutures as possible can be taken to reconstruct the blood circulation. Postoperative treatment (1) The patient should be kept in bed in a quiet state for 7 to 10 d. The room temperature should be maintained at 25℃ frequently. (2) Use anticoagulation and antispasmodic drugs: routinely use low molecular dextrose 1000ml, 24h maintenance drip, for about 7d. Small dose heparin therapy 5-7d, gradually reduce the amount. If necessary, use 30mg of poppyine injection, intramuscular injection once/6h. (3) The use of antibacterial drugs: use as appropriate according to the severity of tissue damage and the severity of contamination, etc. Avoid the use of antibiotics that are more irritating to blood vessels. Results There were 16 cases in this group, 15 cases completely survived. 1 case with 20% skin necrosis survived by secondary flap repair. The postoperative follow-up ranged from 3 to 12 months, and the shape and function were satisfactory. 2. Discussion (1) The survival rate is very low if the composite tissue block is only sutured in situ when it is severed. If the tissue block is large, the possibility of survival is minimal. If the stage I surgery fails or if the tissue block with in situ suture survives, the stage II surgery such as skin grafting, flap grafting, bone grafting, etc. is still needed, which undoubtedly increases the patient’s injury and pain. Therefore, the best method is to adopt microsurgical techniques for tissue block replantation to achieve stage I survival. (2) Composite tissue block severance can be divided into skin-fascia type, muscle (tendon) skin type, (soft) bone skin type and tendon bone skin type. According to the situation of blood vessels in the tissue block, it can be divided into arterial type and total venous type. In this group of 16 cases, 7 cases were cutaneous fascial type, 4 cases were myofascial (tendon) skin type, 2 cases were (soft) bone skin type, and 3 cases were tendon bone skin type. Among them, 14 cases were arterial type and 2 cases were total venous type. 14 cases of arterial type were successfully replanted by direct suturing, bridging and vascular transfer of well-known arteries or small arteries. In one case of total venous type, arterial-venous grafting was used to bridge the artery and vein, which was also successful. In another case, the dorsal tendon-bony-skin composite tissue block of the middle finger was severed with a size of 1.5 cm×1.5 cm, and the artery on one side of the finger was severely damaged, so it was not possible to perform venous bridging surgery, so only the vein was sutured for reimplantation. The case was followed up for 6 months and the finger bone healed well with good shape and function. Analysis of this case shows that firstly, the finger site is more resistant to hypoxia and can maintain blood circulation with a small amount of blood supply; secondly, the amount of tissue in this case is small and the relative oxygen consumption is low, so even if only two veins are sutured, most of them can survive.