[Abstract] Objective To investigate the microsurgical repair methods and clinical results of soft tissue defects of the end phalanges of the thumb. Methods According to the different conditions of soft tissue defects of the end thumb, 5 flaps were used for repair, including 8 cases of dorsal retrograde fascial flap of the first metacarpal, 9 cases of dorsal retrograde insular flap of the ulnar side of the thumb, 13 cases of dorsal insular flap of the index finger, 2 cases of lateral insular flap of the finger artery, 3 cases of [nail flap, and 2 cases of simultaneous use of dorsal retrograde fascial flap of the first metacarpal and dorsal insular flap of the index finger. One case of thumb wound infection at 7 days postoperatively with [nail flap repair was controlled and the graft survived after reopening surgery, one case of dorsal insular flap of the index finger had poor blood supply on the second day, and blood flow was restored after prompt treatment, and one case of distal epidermal necrosis of the dorsal retrograde fascial flap of the first metacarpal was spontaneously healed after dressing change. The rest were viable. At follow-up from 6 to 24 months, two cases had slight restriction of interphalangeal joint function, while the other patients had good function and sensory function recovery between S1 and S3+. Conclusion The selection of an appropriate flap for the repair of soft tissue defects of the end thumb can achieve satisfactory clinical results. Soft tissue defects of the end thumb are not uncommon in clinical work, and with the development of microsurgical techniques, a variety of methods can be applied to treat them, but the choice of treatment needed for a specific case remains a key consideration for clinicians [1-4]. In our department, between January 2002 and January 2008, five flaps were used to repair this type of soft tissue defect according to the local condition of the patient, and are summarized below. Data and methods I. Clinical data There were 37 cases in this group, including 24 males and 13 females. Age ranged from 17 to 52 years old, with an average of 27.4 years old. Cause of injury: 5 cases of chainsaw injury, 24 cases of stamping injury, 8 cases of avulsion injury. Injury finger: 12 cases on the left side, 25 cases on the right side. The extent of injury: 6 fingers with apical tissue loss, 12 fingers with ventral tissue loss, 9 fingers with dorsal tissue loss, 5 fingers with lateral tissue loss, and 5 fingers with dehiscence injury. There were 10 cases of combined end phalangeal fractures and 16 cases of partial end phalangeal defects. The area of the defect: 1.0 cm × 1.5 cm to 3.0 cm × 6 cm. flap application: 8 cases of dorsal retrograde fascial flap of the first metacarpal, 9 cases of dorsal retrograde insular flap of the ulnar side of the thumb, 13 cases of dorsal insular flap of the index finger, 2 cases of lateral insular flap of the finger artery, 3 cases of [nail flap, 2 cases of simultaneous use of dorsal retrograde fascial flap of the first metacarpal and dorsal insular flap of the index finger. The flap area: 1.5 cm × 2.0 cm to 3.5 cm × 6 cm. 26 cases were repaired in an emergency and 11 cases were repaired in 7 to 30 days. The nail flap transplantation was performed as an elective repair. The thumb was thoroughly debrided, and the fracture was fixed with a kerf pin if there was a combined end phalangeal fracture. According to the size and location of the defect, the following five flaps are selected for repair; 1. Dorsal retrograde fascial flap of the first metacarpal: The flap is designed with the median line between the radial edge of the nail root of the thumb and the radial edge of the first metacarpal, with the proximal end of the flap reaching the carpometacarpal joint and the distal end reaching the proximal 1 cm of the interphalangeal joint of the thumb. The dorsal interphalangeal joint of the thumb is 1 cm proximal to the point of rotation. The skin was incised on the radial side of the proximal phalanx of the thumb, and the flap was transferred to the soft tissue defect area through the tunnel, and an end-to-end anastomosis was performed between the endothelial nerve and the broken end of the palmar phalanx of the thumb. Two cases in this group did not undergo nerve anastomosis. The donor area was free grafted with a medium-thickness skin flap. 2, retrograde island flap of the dorsal ulnar aspect of the thumb: the line connecting the ulnar aspect of the carpometacarpal joint and the ulnar aspect of the interphalangeal joint of the thumb was used as the axis, the proximal end of the flap could reach the carpometacarpal joint and the distal end could reach the metacarpophalangeal joint, the ulnar aspect of the metacarpophalangeal joint and the ulnar aspect of the interphalangeal joint could be used as rotation points, the tip should include the dorsal ulnar artery of the thumb, with about 1 cm of fascia, the flap was transferred to the soft tissue defect area through the tunnel, and the endothelial nerve of the flap was anastomosed to the thumb The flap was transferred to the soft tissue defect area through the open channel, and the endodermal nerve of the flap was anastomosed with the severed end of the palmar phalangeal nerve. Three cases in this group did not undergo nerve anastomosis. The donor area was free grafted with a medium-thick skin slice. 3. Dorsal island flap of the index finger: The flap was designed on the dorsal side of the proximal phalanx of the index finger, on both sides to the lateral midline. The axis of rotation is the line between the radial margin of the metacarpophalangeal joint and the snuff bottle, and the flap is lifted superficially in the peritendinous tissue of the extensor tendon, with the anatomical plane of the tip located in the superficial layer of the first interosseous dorsal muscle, which must contain the first dorsal metacarpal artery with 1.5 cm wide deep fascia, covering the thumb trauma after the transposition of the mondo. The donor area is transplanted with a full-thickness skin slice. 4.Lateral island flap of the finger artery: This flap is supplied by the finger artery and common finger artery. The flap is designed at the ulnar side of the middle finger near the middle joint (usually the flap should not exceed the distal interphalangeal joint), and the flap does not exceed the middle metacarpal line and dorsal midline of the middle finger on both sides. The flap contains the ulnar finger vascular nerve bundle, and the flap is lifted in the superficial layer of the tendon sheath, and the tip containing the vascular nerve bundle is freed to the level of the superficial palmar arch and transferred to the recipient area through a subcutaneous tunnel. The donor area is grafted with a medium-thick skin slice. 5, [nail flap: This flap is supplied by anastomosing the dorsalis pedis artery – the radial artery. The flap is designed on the ipsilateral [toe, and the [nail flap with the dorsalis pedis artery and the saphenous vein as the tip is cut in the usual way, severed and transplanted to the recipient area, with end-to-end anastomosis of the toe – finger nerve, the deep branch of the dorsalis pedis artery – radial artery, and the saphenous vein – cephalic vein. The donor area was implanted with skin. Results All the flaps in this group were found to be viable. In one case, the thumb wound was infected 7 days after surgery with a [nail flap, and the infection was controlled and the graft survived after 2 weeks of invasive surgery. 1 case showed a dorsal insular flap for repairing a distal radial aspect of the thumb, and the blood supply to the flap was poor on the second day after surgery. It healed spontaneously after dressing change. Postoperative follow-up ranged from 6 to 24 months, with a mean of 15 months. The flap had good blood flow, texture, and elasticity; one case had a mild flexion deformity of the interphalangeal joint of the thumb, with a flexion angle of about 15°; one case had a slightly limited flexion function of the thumb, with a maximum flexion of 40°, and the rest of the thumb had good function. The range of motion of the interphalangeal joints ranged from 15° to 70° (average 56°), and the range of motion of the metacarpophalangeal joints was normal. The thumb could be normal to the palm and to the fingers. The sensation of the flap was partially restored, and according to the 1954 British Medical Research Council criteria for recovery of sensory function, the anastomosis of the nerve reached S1 to S3, and the unanastomosis of the nerve reached S1 in 1 case, S2 in 3 cases, and S3 in 1 case. In those with their own nerve (lateral insular flap of the finger artery and dorsal insular flap of the index finger), the sensation was restored up to S3+, and the discrimination of the two points was between 5 and 9 mm, with an average of 7 mm. DISCUSSION The thumb accounts for 40% to 50% of the function of the entire hand, and any loss of tissue in any part of the thumb can result in loss of function of the entire hand, so careful repair is imperative. Soft tissue defects of less than 1 cm on the palmar side of the terminal phalanx of the thumb can be repaired by drug exchange or V-Y advancement flaps, while soft tissue defects larger than 1 cm generally require flap repair. The following characteristics of the end thumb need to be considered when choosing which flap to use for repair: (1) The length of the thumb should be restored as much as possible. The thumb requires a certain length for pinching, clenching, and finger-to-finger function to be coordinated with the other fingers; (2) the palmar side of the thumb has hard and tough skin and is rich in free nerve fibers and tactile vesicles; therefore, soft tissue defects on the palmar side should be restored with as much nerve function as possible; and (3) the thumb has only two joints, so it is crucial to maintain normal joint mobility. After flap transposition to repair the soft tissue defect, it is necessary to be able to make the interphalangeal joint move freely, otherwise it will lead to the limitation of joint function. In this group of cases, we chose five flaps, all of which are commonly used in clinical work and have a reliable blood supply. [The nail flap is generally used in patients with avulsions of the thumb containing nail loss at the end of the thumb with high cosmetic requirements. Compared with other flaps, this flap is more risky and the donor implants are often not easily survived, and even if they do survive, they are prone to breakage. In order to improve the success rate of free skin grafting, we improved the traditional packing and pressure method, and generally used closed negative pressure drainage to evenly pressurize the foot wound, with the negative pressure controlled between 150 and 250 KPa, and removed the negative pressure drainage device after 7 days, with better results. In recent years, for patients with emergency thumb end-joint dehiscence injuries, we have used the dorsal retrograde fascial flap of the first metacarpal and the dorsal island flap of the index finger to repair them after tiling, and their efficacy is satisfactory, and they can basically replace [the nail flap free graft, only the shape is not as good as [the nail flap. The lateral insular flap of the finger artery can directly provide the vascular nerve bundle of the flap, its location is hidden, and the color and texture of the flap are similar to that of the recipient area, so it has obvious advantages for the repair of soft tissue defects of the finger tip and the finger belly. However, the clinical application is somewhat limited because of the sensory dysfunction of the donor finger. The dorsal island flap of the index finger is widely used in clinical practice, but it should be used with caution for soft tissue defects at the tip of the thumb and on the radial side, where the tip is under greater tension. In the present case, one patient with flap vascular crisis and one patient with postoperative flexion dysfunction were repaired with the dorsal insular flap of the index finger. This flap contains a direct branch of the superficial branch of the radial nerve, so that sensation can be reestablished after flap survival, which is particularly useful in cases of soft tissue defects on the dorsal aspect of the thumb and in cases with partial defects of the malleolus. The blood supply of the retrograde dorsal insular flap is mainly from the dorsal ulnar artery of the thumb, which anastomoses with the dorsal branch of the innominate artery of the thumb at the proximal phalangeal neck, and the blood supply of the flap is very reliable as long as the communicating branch is not damaged. There are several superficial branches of the radial nerve within the flap cut, which can be easily anastomosed with the lateral palmar nerve dissection to restore sensation intraoperatively. The dorsal retrograde fascial flap of the first metacarpal is comparable in texture and color to the skin of the defect area [5], and the skin of the palmar side of the interphalangeal area can be used to repair the finger belly with a close skin pattern and good shape, and sensory function can be restored by nerve anastomosis. However, the dorsal thumb artery in this flap is small and has no anastomotic branch to communicate with the palmar innominate artery, so the blood supply is not as good as that of the retrograde insular flap on the dorsal ulnar side of the thumb. These two flaps have longer tips and can be used to repair defects at the tip of the terminal phalanx, the ventral aspect of the finger, and the ulnar or radial aspect. In this group of cases, when we cut the flap, the tip is usually with about 0.5 cm of skin tip and is transposed through the bright channel, which greatly reduces the chance of vascular compression at the tip and can effectively improve its venous return and increase the survival rate of the flap; the donor area is not directly sutured, and all implants are wrapped with pressure, which reduces the possibility of tiger’s mouth contracture and limited joint function in the thumb.