The Anterolateral Thigh (ALT) Flap
The alt Flap
A skin, fat and fascia flap it can be thinned free of fascia. Or the skin and fat can be removed to make it a fascial flap. It can be made up to 8 x 25 centimeters, or larger if the donor area is grafted.
Innervation: Yes - lateral femoral cutaneous nerve of the thigh.
Blood supply: Descending branch of lateral femoral circumflex artery.
Artery: 1.5 to 2.5 millimeters
Vein(s): Slightly larger than artery when taken to the origin.
Pedicle length: Up to 7 centimeters.
In the right patient, the skin and subcutaneous fat of the anterolateral thigh can be quite thin, making this flap a potentially large donor site of supple and sometimes sensate fasciocutaneous tissue. The skin paddle can be as large as 8 by 25 centimeters with primary closure attainable. Wider flaps can be harvested if the surgeon is prepared to skin graft the donor area. The flap has a large caliber pedicle, but the anatomy can be variable. Most flaps in our experience require dissection of musculocutaneous perforators and are infrequently supplied solely by the septocutaneous branches. Musculocutaneous perforators nourish over 80 percent of flaps making this perforator flap dissection potentially difficult and tedious.
Anatomy
The anterolateral thigh flap lies on the axis of the septum dividing the vastus lateralis and the rectus femoris muscles. This is depicted by the flap outline in the figure below on the left. Arterial inflow is supplied by the descending branch of the lateral femoral circumflex artery (middle and right figures below). This branch arises from the profunda femoral trunk. The lateral femoral circumflex artery distributes both ascending and descending branches, the latter supplying the perforators to the anterolateral thigh flap. This descending branch travels deep within the space between the rectus femoris muscle and the vastus lateralis muscle - often deep in the septal plane, but on occasion within the substance of the vastus lateralis muscle or the rectus femoris muscle. This septal plane can be used to identify the artery and flap blood supply if the septum is accompanied by at least one septocutaneous perforatorating artery and vein. In most cases, the descending branch distributes musculotcutaneous perforators to the flap. When it runs its entire course inferiorly in the substance of the muscle, flap dissection can be difficult.
Anatomy of the Thigh
The pedicle can be as long as 7 or 8 centimeters. Depending on the point of ligation, the artery size can vary from 1 to 3 millimeters in size, with the major draining vein running slightly larger. Usually two vena accompany the artery that then merge into one at their apex. The flap can be innervated by a major branch of the lateral cutaneous nerve of the thigh. This branch enters the flap at the superior aspect, and can be traced proximally to provide length.
Flap Dissection
The axis of the surface of the septum between the rectus femoris and the vastus lateralis is marked by a line connecting the anterior superior iliac spine and the lateral patella. This line is divided into thirds for purposes of outlining the flap.
Design and marking the alt flap
The junction of the proximal and middle third is often the site of a perforator that pierces the tensor fascia lata. This point can be incorporated in the flap to keep the TFL perforator as a "lifeboat" in the rare circumstance when the distal perforators are of poor quality or injured during dissection. The junction of the middle and distal third is marked and is also incorporated into the flap. This area defined by the middle third of the axis line generally encompasses all perforating vessels, with a pencil Doppler exam helping to reassure the surgeon that perforators are present. The flap design can be adjusted depending on findings of the Doppler exam.
the flap is outlined
The anterior flap is elevated first, noting any vessels perforating the substance of the rectus femoris. Vessels approaching or near the septum are preserved until the posterior flap is elevated and the nourishing vessels to the flap have been identified with certainty.
Below, two perforators are found. The superior perforator clearly arises out of the rectus femoris muscle. The inferior perforator appears to arise either via the septum or through the vastus lateralis muscle. Both are preserved for the time being.
Anterior Perforators Dissected
The posterior flap is elevated toward the septum, agian checking for major perforating vessels, this time through the vastus lateralis. Here the lower perforator can be seen to travel through the vastus. It should be dissected toward the descending branch of the LCFA. The septum is identified and any septal perforators are noted. If there are, and they are large, they can be used to perfuse the flap.
posterior perforators dissected
If one or two good quality perforators are visualized in the septum, then the anterior elevation can continue until the septum is isolated both medially and laterally. If the blood supply is entirely septal, the descending branch of the lateral femoral circumflex artery is found at the base of the septum between the rectus femoris and vastus lateralis and traced proximally. When a flap perfuses from a transmusclular perforator, then this perforator is traced through the muscle to the descending branch. The size of the perforator will determine whether an additional vessel is needed. Vessels can be temporarily clamped with micro clamps to determine inflow dominance.
posterior perforators dissected
The flap is isolated
The entire flap can then be isolated on the dominant perforator(s) and the descending branch of the lateral circumflex femoral vessels.
For closure, skin and subcutaneous tissue flaps are elevated medially and laterally at a level superficial to the fascia. These flaps are closed with interrupted suture and the skin is then approximated. Although light circumferential pressure can be applied to the thigh post-operatively, we do use a closed suction drain.
Flap variations
Anterolateral thigh adipofascial flap: the flap is harvested without the skin paddle. A thin layer of fat below Scarpa's fascia is preserved with the deep fascia to create a thin fat and fascial flap.
Anterolateral thigh fascial flap: the muscular fascia and pedicle are harvested, and no skin or fat is removed.
Post-Operative Care
Seroma forms rarely, but can be a nuisance post-operatively. The patient is allowed to ambulate as soon as clinically indicated for the flap reconstruction. The drain is usually pulled before discharge.
Bibliography
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Kimata Y, Uchiyama K, Ebihara S, Nakatsuka T, Harii K: Anatomic variations and technical problems of the anterolateral thigh flap: a report of 74 cases. Plast Reconstr Surg 102:1517, 1998
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