Skin, fat and fascia. A portion of the humerus can be used to make this an osteocutaneous flap.
Innervation: posterior cutaneous nerve of the forearm.
Blood supply: posterior radial collateral artery.
Artery: Small caliber, often less than 1.5 mm.
Vein(s): The venae are typically paired and the dominant is similar in size to the artery..
Pedicle length: Short. It does not reach proximal to the proximal edge of the flap unless the flap is designed very distally.
The lateral arm flap provides a consistent vascular pedicle for resurfacing defects necessitating fat and skin coverage. Although a small nerve is present with the pedicle, this supplies sensation to the lateral forearm. The flap can be designed very distally as a lateral forearm flap, making the pedicle much longer. However, if a short pedicle is needed, using the lateral forearm results in a very small caliber lumen artery and vein.
The flap is supplied by the radial collateral artery. It originates from the brachial artery and wraps posteriorly around the humerus, descending on the lateral aspect of the humerus and then branching into an anterior and posterior segments. The posterior branch supplies the lateral arm and lateral forearm flaps.
The vascular anatomy of the lateral arm flap. The flap is supplied by the posterior branch of the radial collateral artery. This branch hugs the humerus as it descends at the base of the lateral intermuscular septum.
The flap is designed on the axis of the humerus. Anteriorly, is the biceps, brachialis and brachioradialis muscles. Posteriorly is the triceps. The radial nerve comes into play when the pedicle is dissected proximally, toward the deltoid insertion. The nerve courses posterior to the humerus from its origin at the brachial plexus. It then courses over the lateral aspect of the humerus, from posterior to anterior. A posterior cutaneous nerve of the forearm branches off the nerve and joins the vascular pedicle of the flap. Identifying this nerve with the pedicle and tracing it proximally allows for straight forward identification of the radial nerve.
Anatomy of the lateral arm flap. The radial nerve travels across the proximal base of the flap. It sends a sensory branch with the pedicle of the flap that supplies the distal lateral arm.
The patient is inducted under anesthesia in the supine position with the arm on an arm table. The entire arm is prepped to the axilla and including the shoulder. A sterile tourniquet may be used for the procedure and must be placed high up in the arm. If the tourniquet interferes with proximal dissection (which it usually does), it must be deflated at the latter part of flap harvest.
The axis of the humerus is marked from the deltoid insertion to the lateral epicondyle. The lateral arm flap is designed with its longitudinal axis on this marking. The skin of the arm is pinched to judge the maximum with of the flap is a large paddle is needed. Usually, four to five centimeters are the widest a flap can be. The flap can be quite long however, from the deltoid insertion to distal to the lateral epicondyle. Alternatively, a lateral forearm flap can be marked using the distal think skin around the lateral epicondyle, as shown in the diagram.
Marking the flap outline. The axis of the flap lies over the lateral intermuscular septum. The more distal the flap is made, the thinner the skin. It can be based very distally, as a lateral forearm flap.
The lateral arm or forearm dissection is essentially the same. The posterior flap is elevated deep to the muscular fascial over the triceps. As the flap is elevated toward the septum, small muscular perforators are encountered that are coagulated with the bipolar forceps or are ligated with hemoclips. The pedicle and septum are identified together. And exposed from distal to proximal.
Posterior flap elevation is performed first. The flap is elevated deep to the muscular fascia. The fascial is peeled anteriorly until the septum is encountered.
The anterior flap is elevated. The fascia is slightly more adherent here to the muscle. Then the flap can be elevated from distal to proximal. The artery and vein at the distal aspect are ligated and divided. Then, staying deep to these vessels, the septum is divided freeing the flap from the humerus. As the dissection proceeds more proximally, the distance between the vessels and the humerus increases, and the dissection is easier. The the radial nerve comes into view proximally.
The anterior aspect of the flap is then elevated until the septum, and then the flap can be raised from distal to proximal. The septal attachment to the humerus is released as the flap is elevated.
To gain more pedicle length and a wider caliber of vessels, the incision can be elongated by extending it proximally. The triceps and brachialis muscles are retracted to identify the proximal pedicle and to ligate branches. Care should be taken not to put retraction pressure on the radial nerve.
The flap Is isolated on the arterial pedicle. Proximal exposure begins to get difficult as the artery travels around the humerus.
The lateral arm flap can also be harvested as an osteocutaneous flap. The wedge of bone with periosteal cuff is harvested under the septum and septal pedicle. A narrow portion of bone approximately 1 to 1.5 centimeters wide can be harvested.
An osteocutaneous lateral arm flap can be elevated by removing corticocancellous bone from the distal humerus. A 1.5 centimeter wide plug can easily be harvested.
Lateral Arm Fascial Flap: The flap can be harvested without a skin paddle, on the deep fascia only, creating a thin fascial flap.
Lateral Arm Osteocutaneous Flap: see above.
The incision can be closed with absorbable sutures, usually over a suction drain. A soft dressing is placed and the patient is allowed to use the arm post-operatively as tolerated.