Online Atlas of Microsurgery

An atlas of microsurgery techniques and principles.

The Anterolateral thigh (ALT) flap

Anatomic considerations

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 thin fascial flap. It can be made up to 8 x 25 centimeters, or larger if the donor area is grafted.
Yes - lateral femoral cutaneous nerve of the thigh.
Blood supply:
Descending branch of lateral femoral circumflex artery.
1.5 to 2.5 millimeters
Slightly larger than artery when taken to the origin.
Pedicle length:
Up to 7 centimeters or longer, depending on how the flap is designed and where the perforator(s) enter the flap.
Marking the ALT Flap

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 of the perforator vessel or vessels can be variable. Most ALT flaps, in our experience, require dissection of musculocutaneous perforator(s) and are infrequently supplied solely by septocutaneous perforators. Perforator dissection can be difficult and tedious to the inexperienced microsurgeon.


Arterial inflow to the anterolateral thigh flap is supplied by the descending branch of the lateral femoral circumflex artery. This branch arises from the profunda femoral trunk. The lateral femoral circumflex 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 (on the surface of the vastus intermedius) - often deep in the septal plane, and on occasion enters the substance of the vastus lateralis muscle as it travels distally. The septal plane can be used to identify the artery and flap perforator blood supply. In most cases, the descending branch distributes musculocutaneous perforators to the flap.

The ascending branch from the lateral femoral circumflex, supplies the TFL flap. It can also supply a perforator to the upper part of the anterolateral thigh. This upper perforator is useful as a lifeboat when the normal ALT perforators are inadequate.

Vascular Anatomy of the ALT Flap

Vascular anatomy of the lateral thigh. The ALT flap is nourished by perforating branches (PBS) from the descending branch (DB) of the lateral femoral circumflex (LFC) vessels.
(PF) profunda femoral
(AB) ascending branch
(*) perforator through TFL muscle to skin.

Anatomy of the Thigh Muslces and ALT Flap

The anterolateral thigh flap lies on the axis of the septum dividing the vastus lateralis and the rectus femoris muscles.

Anatomy of the Thigh Muslces and ALT Flap

The flap is outlined on the axis of the anterior superior iliac spine and the lateral patella. Perforators can be marked with a pencil Doppler to help design the outline of the flap.

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 veins accompany the artery and then merge into one at profunda femoral vein junction. 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.

Marking the ALT Flap

The maximum width of the flap is judge with a pinch test. Donor sites that can not be primarily closed are skin grafted.

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. The flap design can be adjusted depending on findings of a Doppler exam.

The Flap is Outline

The anterior flap is raised and perforators are identified to the flap and spared.

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.

The Anterior Flap is Dissected

The posterior flap is elevated and the perforators to the flap are surrounded. The dominant perforator(s) is chosen.

The posterior flap is elevated toward the septum, again 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.

Dissection of the Posterior Flap

The perforators usually travel through muscle and must be dissected free. A bipolar cautery can be used.

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 trans muscular 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 microvascular clamps to determine inflow dominance.

The Perforator and Pedicle are Dissected

The pedicle can be traced to the origin to gain length.

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.

The Perforator and Pedicle are Dissected

The flap can be harvested with just fascia and a small amount of overlying fat to create a thin fascial flap.

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.


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