The medial side of the forearm flap (from Dai Zixing's "Flap Internal Superstition 483") was first introduced by Chinese scholar Yang Guofan as the donor site for the lateral side of the forearm. It is one of the two flap donor sites created by Chinese scholars and widely recognized abroad (the other being the anterolateral thigh flap). Currently, Chinese scholars have conducted in-depth research on the donor area of the radial artery, discovering many ways to reduce the damage to the donor site on the radial side of the forearm, such as: 1. Radial artery retrograde island flap without skin; 2. Radial artery styloid perforator flap; 3. Radial artery snuffbox perforator flap, etc. The appearance of distally pedicled fasciocutaneous flaps and fascial flaps supplied by the perforators of the radial artery has simultaneously overcome these two major defects. Currently, in clinical applications in hand surgery, distally pedicled perforator flaps have almost completely replaced the radial artery retrograde island flap. The radial artery flap refers to a series of flaps located on the radial side of the forearm with the radial artery-vein bundle as the vascular pedicle. In 1981, Yang Guofan first reported the clinical application of free transplantation of the forearm flap with the radial artery as the vascular pedicle. Subsequently, Wang Wei, Lu Xiehua, and others successively reported the clinical use of reverse island flaps of the forearm for repairing hand wounds. Foreign scholars refer to the forearm radial side flaps and their reverse island flaps with the radial artery-vein bundle as the vascular pedicle as the "People's Republic of China Flap". In 1985, Zheng Yuan'an reported the experience of using a reverse composite island flap with a piece of radius bone from the forearm flap for primary thumb reconstruction, expanding the scope of application of the radial artery flap. The radial artery flap is an axial flap nourished by the main artery and its branches. Its anatomical basis is that the artery gives off numerous branches, forming a rich vascular network and anastomotic branches that nourish the entire forearm skin. The main advantages of the flap lie in the fine caliber of the vessels, deep position, long surgical variation, simple surgical operation, good texture and color of the flap, abundant subcutaneous fat, and even thickness that makes it easy to shape. Its biggest disadvantage is that harvesting the flap not only sacrifices an important artery with minimal loss but also leaves noticeable scars on the forearm, affecting aesthetics. The author believes that when selecting and using this flap, strict control of indications should be exercised, and excellent cosmetic and functional repair of the donor site should be advocated, suggesting that after the flap is harvested, the radial artery defect should be repaired with a vein graft. [Anatomical Use] After branching from the brachial artery in the elbow fossa, the radial artery runs downward along the lateral side of the brachioradialis muscle, within the deep surface of the brachioradialis muscle. Its medial edge consists of the upper third of the pronator teres muscle and the lower two-thirds of the flexor carpi radialis muscle. The anterior side of the artery, from top to bottom, sequentially includes the supinator muscle, flexor digitorum superficialis, flexor pollicis longus, and abductor pollicis brevis muscles. According to its positional relationship with the brachioradialis muscle, the radial artery can be divided into two parts: the upper two-thirds are covered by the brachioradialis muscle, with an average length of 11.7 cm, known as the covered portion; the lower one-third is superficial, directly located under the skin, covered only by the superficial and deep fascia, with an average length of 10 cm, known as the exposed portion. The outer diameter of the radial artery at its origin averages 2.7 mm, and at the junction between the covered and exposed portions in the middle of the forearm, the outer diameter is 2.3 mm. Both the proximal and distal ends of the new radial artery flap can be used as recipient areas for anastomosis. Except for the two major branches, the radial collateral artery at the proximal end and the superficial palmar branch at the distal end, the blood supply of the flap is mainly formed by many cutaneous and muscular branches given off from both sides during the course of the forearm. Among them, the cutaneous branches of the covered portion number 0-10; the cutaneous branches of the exposed portion number 4-18, averaging 9.0 branches. The outer diameters of these cutaneous branches range from 0.1-1.1 mm, with most being 0.2-0.5 mm. They form a rich vascular network in the subcutaneous tissue of the forearm and have extensive anastomoses with the cutaneous branches of the ulnar artery, interosseous artery, and lower end of the brachial artery, allowing the incision range of the flap to far exceed the range supplied by the cutaneous branches of the radial artery. The maximum area of the flap can reach 35 cm x 15 mm. During the transplantation of a retrograde island flap, the flap relies on the arterial arch of the palm for retrograde blood supply. The radial artery has two constant accompanying veins, and the return veins of the flap can choose either the cephalic vein or the accompanying veins of the radial artery. The cephalic vein is the main superficial vein for the return flow of the flap. It originates from the radial side of the back of the hand, ascends along the radial side of the forearm accompanied by the superficial radial nerve, and has branches entering the median cubital vein at the elbow fossa. In the middle of the forearm, the diameter of the cephalic vein averages 2.8 mm. The flap transplantation mostly uses the cephalic vein as the return vein. The radial artery has two accompanying veins, with multiple bridging anastomotic branches between the two veins. The average outer diameter of the accompanying veins of the radial artery is 1.3 mm. When performing free transplantation of the flap, the vein usually anastomosed is the cephalic vein, and choosing to anastomose the accompanying veins of the radial artery also allows the flap to survive. During the transplantation of a retrograde island flap, venous return relies on the "maze return" of the bridging anastomotic branches of the accompanying veins of the radial artery. The lateral cutaneous nerve of the forearm is one of the terminal branches of the musculocutaneous nerve. It emerges from the deep fascia laterally to the biceps brachii muscle in the elbow fossa, located beneath the cephalic vein. Its upper end has an average diameter of 3.0 mm and can serve as the sensory nerve for the flap. [Indications] The forearm flap has constant vessels, long pedicles, fine calibers, and is difficult to anastomose, making it one of the most commonly used flaps in clinical free transplantation. Due to its poor skin color and relatively hard texture, it is suitable for repairing soft tissue defects in the face and neck and tracheal reconstruction. 1. Organ reconstruction, such as total nasal reconstruction, penis reconstruction, tongue reconstruction, and orbital reconstruction. 2. Reconstruction of hard tissue defects in the oral and maxillofacial region, including soft tissue defects after tumor resection in the facial region, traumatic scar deformities, and repair of soft tissue defects in the floor of the mouth. 3. Repair of large-scale skin and soft tissue defects in the hand caused by trauma. When there is no good donor site available, this flap can be used for severe contractures or normal repairs in the hand, as well as for correction of thumb contracture. 4. Thumb reconstruction, where the forward island flap combined with iliac bone grafting can be used for thumb reconstruction. 5. It can be used as a serial flap, carrying other flaps for transplantation. [Surgical Techniques] 1. Free Flap Transplantation 1. Flap Design: Draw a longitudinal axis line from the midpoint of the elbow fossa to the point of radial artery pulsation at the wrist. Since the branches of the radial artery in the exposed part are significantly fewer than in the covered part, when performing free transplantation of the forearm flap, the lower end of the radial artery should be taken as the transverse axis of the flap. The size of the flap to be excised depends on the size of the wound in the recipient area and can include all the skin of the forearm, extending up to just below the elbow. 2. Flap Excision: The surgery is performed under tourniquet control. Make appropriate division incisions on the radial and ulnar sides of the flap according to the design line. Perform blunt dissection toward the midline between the deep fascia and the muscle membrane. Dissect the ulnar side up to the tendon of the extensor carpi radialis muscle and the radial side up to the tendon of the brachioradialis muscle, taking care not to injure the tiny branches coming off the radial artery. The radial artery and vein must remain superficially covered by the flap. Carefully ligate the muscular branches coming off the radial artery. Cut and ligate the ulnar side veins, cephalic vein, radial artery, and accompanying veins at the distal end of the flap. At this point, a forearm flap with the distal radial artery and vein and the tail vein pedicle is created. Before releasing the tourniquet, observe the blood circulation of the flap to ensure that the blood supply to the flap is good before cutting the vascular pedicle and indeed ligating the donor area vessels. 2. Retrograde Island Flap 1. Flap Design: When transferring a retrograde island flap to repair hand wounds, the rotation axis of the flap should be located at the point of radial artery pulsation. Design a tennis racket-shaped flap according to the size of the wound. Before cutting the proximal end of the radial artery-vein bundle, the blood supply must be occluded with a vascular clamp to observe the blood supply situation of the hand and the forearm retrograde flap. If there are no abnormalities, the proximal end of the radial artery-vein bundle can then be cut and properly ligated. The flap can then be transferred through a subcutaneous tunnel to the recipient area for repair. If the volume of the flap is too large and it is difficult to pass through the tunnel, the skin can be directly incised, and appropriate separation can be performed to reduce the tension of the pedicle. The donor area is repaired with intermediate-thickness skin grafts. 2. Flap Excision: The surgery is performed under a tourniquet. First, make an incision at the base of the flap on the radial side of the flexor carpi radialis muscle to expose the radial artery and vein. Identify the direction of the radial artery and cut the skin according to the flap design down to the deep fascia and perform sharp dissection towards the center of the flap from both sides. When approaching the gap between the brachioradialis muscle and the flexor carpi radialis muscle, dissect under the muscle membrane to avoid damaging the large branches coming off the radial artery. Ligate the branches of the radial artery going to the deeper tissues. Once the entire flap is completely freed, clamp the proximal radial artery and vein with a vascular clamp, release the tourniquet, and observe the blood supply to the hand and the flap, as well as the pulse of the distal radial artery. If there are no abnormalities, ligate and cut the vessel bundle near the proximal edge of the flap to form an island flap with the distal radial artery and vein as the pedicle, which can be retrogradely rotated to repair hand wounds. 3. Posterior Arm Radial Osteocutaneous Flap for Thumb Reconstruction Besides supplying the skin through cutaneous branches, the radial artery also supplies muscular and periosteal branches to the deep muscles and radius. By taking a forearm radial side osteocutaneous flap with the distal radial artery and vein as the pedicle and performing a retrograde transfer, the thumb can be reconstructed. 1. Flap Design: About 3 cm above the wrist crease, design a trapezoidal flap with the radial artery as the center, with the upper base being 5 cm and the lower base being 6 cm. The width of the flap should be greater than the size of the reconstructed thumb. 2. Surgical Steps: Make an incision at the base of the posterior arm flap to expose the radial artery. Cut the designed flap according to the plan, retract the brachioradialis muscle radially to expose the radius, and determine the range of the radius segment to be excised. During the procedure, take care to protect the nutrient vessels of the radial vein entering the radius. When excising the radius segment, do not strip the periosteum to ensure the integrity of the bone flap-periosteum-flap complex. Ligate and cut the radial artery distally to form a forearm osteocutaneous flap with the proximal radial artery and vein as the vascular pedicle. Perform a retrograde transfer of the osteocutaneous flap for early thumb reconstruction. Connect the lateral cutaneous nerve of the flap to the digital nerve of the residual thumb to restore the sensory function of the reconstructed thumb. Repair the wound in the donor area with a free skin graft.