The Lateral Arm Flap
The lateral arm flap is a thin, innervated, fasciocutaneous flap with a constant
vascular anatomy. Although brief reports of the anatomy and clinical use of the flap
were available in 1982 (Song), the first comprehensive study was published by
Katsaros et al. in 1984. The vascular anatomy of this flap is based on the posterior
radial collateral artery (PRCA), a branch of the profunda brachii artery.
Another branch of this artery, the anterior radial collateral artery, is variable and
of small caliber, and does not contribute to the flap's vascular supply. The lower
lateral cutaneous nerve of the arm, arising from the radial nerve and piercing the
triceps muscle belly, innervates this flap. The posterior cutaneous nerve of the
forearm also arises from the radial nerve and courses through the flap, continuing
distally to supply the lateral border of the forearm. The PRCA provides at least four
fascial branches from 1 to 15 cm proximal to the lateral epicondyle, the largest of
which is located an average of 9.7 cm superior to the lateral epicondyle.
Technical Considerations
The lateral arm flap is suitable for coverage of soft tissue defects of the dorsal and
volar surfaces of the hand, forearm, foot, anterior tibial surfaces, and face. Because
the undersurface of the flap is fascial, it is an excellent choice for covering tendons or
for situations in which tendon reconstruction is anticipated. The flap is relatively thin
and often free of hair. For this reason, it may also be used for reconstructing intraoral
defects. Its color and thinness also make it useful for facial reconstruction. If a very
thin flap is required, as in reconstruction of a gliding surface, the fascia and its
vascular pedicle may be harvested without the overlying skin and fat. In this way, a
large fascial flap is available with primary closure of the donor defect. Because the
flap is innervated by the lower lateral cutaneous nerve, it may be used for sensory
cutaneous reconstruction. In many cases, a second team may simultaneously harvest
the flap, thus greatly reducing the operative time.
The major landmarks to be identified during flap harvest are the insertion of the
deltoid muscle upon the humerus and the lateral epicondyle of the humerus. The flap
lies midway between these two structures. Dissection may be accomplished with the
patient supine or in a lateral decubitus position. The shoulder may be adducted or
abducted. A narrow sterile tourniquet placed as high as possible about the arm
provides a bloodless field.
The posterior skin incision is made first, extending from the lateral epicondyle to the
insertion of the deltoid muscle. In the region of the cutaneous portion of the flap, the
incision is carried down through the deep fascia enveloping the triceps muscle. The
posterior flap is raised subfascially, tacking the triceps fascia to the skin island to
prevent the flap from shearing off and protecting the perforating cutaneous branches
of the PRCA within the surrounding fascia of the triceps. Dissection continues from
back to the anterior border of the triceps muscle. Here, the fascia dives deeply and
inserts into the humerus. It is within this two-leaved fascial envelope (the posterior
leaf is the triceps fascia and the anterior leaf is the biceps, brachialis, brachioradialis
fascia) that the PRCA lies. When the posterior dissection has been accomplished, the
cutaneous perforators will be visible, and one may then adjust the position of the
anterior incision to include these vessels in the fasciocutaneous portion of the flap.
To harvest the anterior half of the flap, an incision is made overlying the biceps
muscle and carried into the subfascial plane, again tacking the fascia to the skin
island. This dissection proceeds anterior to posterior to the insertion of the fascia into
the bone at the posterior border of the biceps, brachialis, and brachioradialis muscles.
At this point, the cutaneous flap, with its ascending cutaneous perforators, is tethered
by the fascia that inserts into the bone. The distal continuation of the PRCA is then
transected and ligated, and the two leaves of the fascia are released from their bony
insertion. Osseous perforators are ligated as the fascia is separated from the bone. If
bone is to be taken with the flap, the segment is outlined, encompassing the fascial
insertion. The pedicle is dissected proximally, and great care is taken to identify the
radial nerve that lies between the brachialis and brachioradialis muscles. Often the
posterior cutaneous nerve of the forearm is so intimately attached to the flap that
it cannot be separated and must be sacrificed. The dissection continues proximally
until the insertion of the deltoid muscle is reached. Here, the pedicle turns posteriorly
and the PRCA can be followed for a short distance as it travels toward the so-called
spiral groove on the posterior humeral surface. To obtain the maximal pedicle
length, the region of the spiral groove can be entered by dividing the fibers of
origin of the lateral head of the triceps from the humeral shaft. These fibers are
repaired at the conclusion of surgery. In practice, the greatest length of pedicle that
can be obtained is approximately 8 cm. At this level, the smallest outer diameter is
1 mm, but usually the diameter is between 1.5 mm and 2.0 mm. The paired venae
comitantes that accompany the PRCA provide the venous drainage.
Katsaros et al.1 have shown that a donor site of up to 6 cm in anteroposterior diameter
may be closed primarily. Donor sites of greater diameters need skin grafting for
closure. When multiple perforators are found to the proximal and distal portions of the
flap, the flap can be cut through in its central area, providing two islands that can be
folded to form lining and cover for facial defects, or placed side by side to form a
shorter, wider flap.
An area of numbness results along the lateral forearm, innervated by the posterior
cutaneous nerve of the forearm. This is usually tolerated well and decreases
progressively within the first 6 months after surgery.
From proximal to distal, the biceps, brachialis, brachioradialis, and extensor
carpi radialis longus arise from the anterior surface of the septum and humerus.
From the posterior surface of the septum the lateral head of the triceps arises
proximal to the spiral groove and the medial head distal to the groove.
PRS 2000
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lateral forearm skin is perfused by a rich anastomotic plexus consisting of terminal
branches of the posterior radial collateral artery
the presence of this vascular expansion suggests that the forearm extension need
not necessarily be confined to its prescribed axis, but could be volar or dorsal to it,
provided lower lateral arm skin is included.
a territorial overlap exists between the posterior radial collateral artery and the
interosseus recurrent artery - a rich anastomotic network rather than a single,
discrete vessel that continues beyond the elbow.
thus, for safety, a distally sited flap should at least incorporate skin over the lateral
epicondyle.
In the split-flap modification introduced by Katsaros, splitting should be
performed proximal to the epicondyle, where the pedicle is deep, but not distally,
where it is superficial.