A 38-year-old male foreign worker was admitted due to a crush injury on both sides of the 1st web space area. There were severe soft tissue defect and comminuted fracture of the 1st metacarpal and proximal phalanx on X-ray. Initially, exploration, debridement, and Kirschner wire (K-wire) fixation were performed. There was no neurovascular injury.

After 3 days, to address the skin and bone defects, a free osteocutaneous lateral arm flap was performed. A 12×4-cm skin paddle and a 1×3-cm segment of the proximal humerus were harvested. The arterial anastomosis was performed on the dorsal branch of radial artery and the branch of cephalic vein was anastomosed to both commitant veins. The bone fragments were aligned and stabilized using plate and screws.

Four months after the surgery, he was able to maintain his index finger close to normal shape, and he was able to grab objects by flexing the metacarpophalangeal joint. Fig. 1 illustrates the preoperative, intraoperative, and postoperative processes.

A 38-year-old male patient was admitted due to a crush injury and incomplete amputation injury of the index finger. He had severe skin and tissue crush injury at the radial side of the midportion of the index finger and also had severe bone loss in the middle and proximal phalangeal bones. Initially, debridement, wound closure, and fracture fixation were performed, but skin necrosis progressed gradually. To address the skin and bone defects, a free osteocutaneous lateral arm flap was performed. A 6×8-cm skin paddle and a 1×3-cm segment of the proximal humerus were harvested. The arterial anastomosis was performed on the radial digital artery of the index finger. The bone fragments were aligned and stabilized using metal plates and K-wires. Five months after the surgery, he was able to maintain his index finger close to normal shape, and he was able to grab objects by flexing the metacarpophalangeal joint. Fig. 2 illustrates the preoperative, intraoperative, and postoperative processes.

The technique of the lateral arm flap follows the procedure described by Katsaros et al. [2]. The flap is supplied by the posterior radial collateral artery that branches from the brachial artery. The flap design is centered over the axis of the humerus, drawing a line connecting the deltoid insertion and lateral epicondyle. Anteriorly are the biceps, brachialis, and brachioradialis muscles, while posteriorly, the triceps. It is safer to elevate the flap starting from the posterior side to make the dissection plane easier to locate. Since the fascia of the triceps muscle is very thin, it is easy to lose the dissection plane in this area, especially for those less experienced with the procedure. When the dissection plane is not clearly identifiable, the incision should be extended to the tendon part of the triceps muscle. Once the tendon is slightly incised, it can be identified, and the skin, subcutaneous tissue, and fascia should be sutured using stay sutures. The dissection is then continued towards the anterior side, just above the tendon. Using forceps, retract the triceps muscle posteriorly while pulling the stay sutures holding the flap anteriorly to proceed with the dissection towards the anterior side. During this process, numerous vessels supplying the triceps muscle can be identified; these should be ligated or cauterized. As the dissection continues, the intermuscular septum between the triceps and the anterior muscles can be visualized. At this point, the surgeon should palpate the lateral aspect of the humerus with their fingers to reidentify the location of the vascular pedicle and proceed with deeper dissection.

When the dissection reaches the attachment site of the humerus and the intermuscular septum, the vascular pedicle can be identified near the surface of the bone. Leave approximately 2 to 3 mm of the triceps muscle attached to the humerus and proceed with posterior dissection. Since this dissection area often becomes a source of postoperative hematoma, thorough hemostasis should be ensured after flap elevation [3,4].

Dissect the triceps muscle sufficiently to allow the elevation of the required size of bone and complete the posterior dissection. The anterior dissection is performed in the same manner as the posterior dissection. During dissection, nerves responsible for the sensory innervation of the forearm can be identified in the subcutaneous tissue and should be preserved if possible. The feasibility of nerve preservation depends on the individual’s anatomical structure. When the intermuscular septum is encountered during posterior dissection, the dissection direction should be redirected towards the humerus. Care must be taken when retracting the anterior muscles with forceps, as the radial nerve may be damaged by the forceps.

Upon reaching the lateral border of the humerus, retain approximately 2 mm of muscle attached to the humerus and elevate the muscle as needed to expose the bone. Before harvesting the bone, continue the dissection proximally until vessels of a size similar to those at the recipient site are identified. Special caution is required during proximal dissection, as the radial nerve becomes exposed. At the point where the radial nerve is exposed, the vascular pedicle typically has a diameter of 1–2 mm; proceeding further proximally may reveal cases where only a single accompanying vein is present. To ensure adequate blood supply, the inclusion of a bone segment between 3 and 6 cm above the lateral epicondyle is recommended.

After completely dissecting the vascular pedicle, harvest the required amount of bone. Since the lateral border of the humerus is thin and sharp, precise measurements of the harvesting site are necessary to avoid harvesting only cortical bone. After harvesting the bone, ensure that the distal end of the vascular pedicle is properly ligated and confirmed. The elbow region has abundant vascular connections, and inadequate hemostasis above this area can result in postoperative hematomas due to bleeding.

If there is no tension at the donor site, primary closure is possible. However, if the tension is excessive, there is a risk of compartment syndrome, so skin grafting is recommended.