The Anterolateral Thigh Flap

In selected patients, the skin and subcutaneous fat of the anterolateral thigh can be quite thin, making this flap a potentially large donor site of supple and 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.  It is not recommended for the inexperienced microsurgeon.

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 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.  If no septocutaneous perforators are present, the superior portion of the septal plane that meets the tensor fascia lata muscle can be used to find the lateral femoral circumflex vessels of the descending branch.  In 80% of cases, the descending branch distributes musculotcutaneous perforators to the flap.  When it runs its entire course inferiorly in the substance of the rectus femoris muscle, flap dissection can be difficult.   

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 2 millimeters in size, with the major draining vein running slightly larger.  Usually two venae accompany the artery.

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.  The junction of the proximal and middle third is often the site of a perforator that pierces the tensor fascia lata.  We mark this and incorporate this point in the flap.  The TFL perforator can be 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.  We do not as a rule  use a pencil Doppler probe to try to identify perforators.  We have found this is sometimes not accurate and the method of incorporation of the middle third of the septal axis is extremely reliable.  The flap can later be shortened after harvesting when direct visualization of perforators can be done. 

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 posterior flap can be elevated to the septum usually without interference from major perforating vessels in the vastus lateralis.  The septum is identified and any septal perforators are noted.  

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.  The lateral femoral circumflex artery and vein can then be isolated as the proximal pedicle.  

If no septal vessels are found, the perforators through the rectus femoris must be traced within and through the muscle to the descending branch of the lateral femoral circumflex artery.  The vessels are then isolated as above to the origin on the lateral femoral circumflex artery and vein and the flap is ready to be transferred.

The branch through the TFL, with or without TFL muscle, can be isolated to augment the blood supply, but is usually ligated and divided to enhance the mobility of the proximal pedicle.  The ascending branch likewise is divided and the flap is isolated on the lateral femoral circumflex 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. 

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 reconstruction.

Bibliography

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