The Anterolateral Thigh Flap for Lower Extremity Reconstruction

ABSTRACT

The anterolateral thigh flap can be considered to be one of the workhorses of perforator flaps. Its ease of dissection together with the long and reliable pedicle make it extremely suitable as a free-skin flap. The versatility of the flap allows for multiple skin islands on one pedicle, “chimeric” type of flaps, and proximally and distally based local pedicled flaps as well. However, especially in the Caucasian patient, the flap can be rather thick, and the donor-site morbidity is not always accepted, which limits somewhat its popularity in lower extremity reconstruction, though in selected cases it proves to be an extremely useful adjunct to our reconstructive possibilities of the lower leg.

Since its introduction in 1984 by Song et al,¹ the anterolateral thigh flap has gained widespread popularity, especially in Asian countries, where it has replaced the radial forearm flap as being the workhorse in head and neck surgery. Popularity of the anterolateral thigh flap in Asia is reflected in the numerous reports from oriental authors. Though initially essentially used in head and neck reconstruction, the anterolateral thigh flap gained more and more appreciation in other reconstructive areas, in so far that Wei et al in their experience of over 2000 flaps consider it to be the “ideal” soft tissue flap.^2,3,4,5,6 Anterolateral thigh flaps have been introduced in breast,⁷ genital,⁸ and upper⁹ and lower^4,10,11 extremity reconstruction.

ANATOMY

Blood supply of the anterolateral thigh depends upon perforators from the descending branch of the circumflex femoral pedicle. Classically the descending branch originates out of the profunda femoris, together with the ascending and transverse branch, deep to the rectus femoris and sartorius muscles. It descends on the medial border of the vastus lateralis muscle, sometimes dividing in a lateral and medial branch. The lateral branch courses distally in the septum between vastus lateralis and rectus femoris muscle, where it gives off septocutaneous and musculocutaneous perforators, the latter piercing the vastus lateralis muscle. The medial branch descends under the rectus femoris muscle where it gives off perforators, which pierce this muscle to supply the anteromedial part of the thigh skin. Substantial anatomical variation does exist though in the origin and course of the different branches of the lateral circumflex pedicle. However, as long as one keeps to the principles of perforator flap surgery, careful retrograde dissection close to the vessel, this has little or no clinical implication. All ways lead to Rome. If necessary pedicle lengths up to 12 cm and more can be expected.²

The descending branch of the circumflex femoral artery is reported to anastomose with the lateral superior genicular artery or branches of the profunda femoris, which allows for the raising of a distally based anterolateral thigh flap with a pivot point 3 to 10 cm above the knee, to close defects around the knee joint.^12,13,14 Local V-Y advancement or propeller-type flaps, based on limited mobilization of one single perforator, can also be designed to allow for closure of more proximal upper leg defects.¹⁵ Dissecting out the descending branch allows for pedicled flaps, which will reach the genital region (Fig. 1), or even the lower abdomen.

Figure 1.

(A) Defect after resection of a recurrent vulvar carcinoma. (B) Two pedicled anterolateral thighs outlined on the thighs. (C) Late postoperative result.

SURGICAL TECHNIQUE

Most important perforators are to be expected in a 3-cm circle centered on the midpoint of a line connecting the anterior superior iliac spine and the lateral border of the patella. Color Doppler flowmetry has been shown to be a very reliable way, with a high predictive value, to localize the perforators.^16,17 On the other hand, Wei and Mardini¹⁸ proved that freestyle free flaps can be safely harvested based on simple audible Doppler ultrasonography, the idea being that every perforator with a clear audible Doppler signal supplies a certain size of skin island and can be traced back retrograde until sufficient pedicle length and/or vessel size is reached to provide for a safe anastomosis. The lateral circumflex pedicle can be followed up to the level of the superficial femoral vessel; some caution is warranted in the vascularly compromised patient where ligation of the profunda system could evoke ischemic insults.¹⁹ Though the exact amount of tissue each perforator will supply cannot be judged beforehand, in the anterolateral thigh region skin paddles up to 35 by 25 cm have been safely raised on one single perforator. On the other hand, chimeric type flaps can be raised including separate skin islands on different perforators and/or muscle on individual muscle branches.^20,21 To lengthen the pedicle the perforator can be eccentrically located at the more proximal edge of the flap.

Flap widths of up to 8 cm can usually be primary closed. Wider flaps need skin grafting of the donor area, though preexpansion or the use of local flaps has been advocated to allow for primary closure.^22,23

Dissecting the flap on top of the muscle fascia (Fig. 2A) makes it thinner and more pliable and avoids muscle herniation; identification of the perforators is slightly more troublesome though. It also allows for preservation of the sensory nerves that run on top of the muscle fascia. Dissection underneath the fascia allows for easier isolation of the perforators and spares the suprafascial plexus (Fig. 2B), and skin grafts heal better on the bare muscle in the larger flaps.

Figure 2.

(A) Suprafascial approach to the perforator, clearly outlining also the vascular network in the loose areolar tissue on top of the muscle fascia. (B) Dissection underneath the fascia on top of the muscle where dissection tends to be easier and the perforators bigger. A clear distinction can be made between the artery and its venae commitantes.

Several authors report successful thinning of the flap up to the subdermal plexus, resulting in a “superthin” skin flap of 2 to 4 mm.^24,25,26 Thinning is mostly restricted to the periphery of the flap, though, leaving a central core of at least 2 cm around the perforator intact, which as such only partially solves the problem. Studies on the arterial and venous anatomy within the fat layer of the flap suggest different types of branching of the perforator.²⁷ There seems to be a dual type of venous outflow within the flap, of which the dominant type does not coincide with the arterial anatomy. This also suggests that meticulous care should be taken in thinning of the flap. Our experience with thinning is rather disappointing, often resulting in flap suffering and partial necrosis, which was confirmed in the study by Alkureishi et al.²⁸ Rather, we prefer to thin the flap if necessary by extensive liposculpture in a second stage, 3 to 6 months later. This sometimes necessitates staged interventions in the thicker patient: first skin grafting the edges of the flap (Fig. 3) to allow for tension-free insetting, and later on eventually excising the excess skin and grafts after defatting of the flap by liposculpture.

Figure 3.

In the thicker flaps, instead of thinning them, one can also skin graft the edges to be able to close the defect without undue tension; the skin graft can later be excised after thinning of the flap by liposuction.

The pedicle can be raised including the distal part of the descending branch, or even part of the profunda femoris, which not only allows for an easier end-to-end rather than an end-to-side anastomosis, both venous and arterial, but also enables flow-through reconstructions in case of vascular lesions^29,30 (Fig. 4).

Figure 4.

(A) Including part of the distal descending branch allows for flow-through anastomoses, which not only allow for easier and safer end-to-end anastomoses without disrupting the vascularity to the distal leg but also allow for flow-through reconstructions in case of vascular lesions. (B) The anterolateral thigh flap with its T-type pedicle. (C) The “T” of the descending branch interpositioned in between proximal and distal posterior tibial artery and vein.

DISCUSSION

In the reconstruction of lower limb defects, the idea still prevails that muscle flaps are a prerequisite to cope with infection. There is little or no substantial evidence though to prove the superiority of muscle flaps compared with well-vascularized skin flaps. Clinical evidence supports the idea that skin flap coverage in itself is sufficient, if only adequate debridement and hemostasis, mechanical rinsing, and obliteration of dead spaces have been performed.

Essentially what we are looking for in the majority of cases of lower extremity reconstruction are thin, large, and well-vascularized skin flaps, with long pedicles of adequate size, nice texture match, and minimal donor site morbidity. The thickness of the flap has a substantial influence on the necessary width of skin to close the defect, as for each increment of 1 cm in a circumferential lesion, the necessary amount of skin changes by 6.3 cm. The success of the anterolateral thigh flap in head and neck surgery is probably also partially related to the fact that the patients tend to be emaciated, which allows for the harvesting of nice thin flaps on the thigh.

The anterolateral thigh flap has all the advantages of most perforator flaps: a large skin island, reliable and long pedicle, and depending on cultural biases, acceptable donor-site morbidity. On top of that, dissection is fairly easy; the anterolateral thigh flap became our preferred choice in humanitarian missions, where frequently surgery has to be performed under less than ideal circumstances, with no muscle relaxation, no bipolar coagulation, no hemoclips, and limited instrumentation, time, and resources (Fig. 5). Different chimeric types of flap can be conceived, and the large side branches of the circumflex femoral system allow for flow-through anastomoses. In the lower leg, the possibility of harvesting a flap on the same leg without further functional impairment offers an additional advantage. The pedicled flaps are very useful in the otherwise rather difficult to treat knee region and offer a nice alternative to the classical saphenous flap.

Figure 5.

(A) Chronic burn wound and contracture in a young Cambodian monk who used to walk barefoot through the streets, presented to us during one of our “cleft lip” humanitarian missions. (B) Early postoperative result after debridement showing release of the contracture and free anterolateral thigh coverage.

However, with the plethora of different type of flaps available, donor-site morbidity and the exact matching of the flap with the recipient site to increase functional and esthetic outcome become more important considerations (Fig. 6). With this, cultural differences come into the issue. Seemingly, Asian patients tend to be leaner than Western patients and are more willing to accept the scar and the eventual contour deformity on the thigh, which can occur even after primary closure. Moreover, defatting the flap seems to be more difficult than generally accepted.

Figure 6.

(A) Defect of the lower limb in a 37-year-old female after resection of a recurrent sarcoma of the lower limb. (B) Early postoperative result after coverage with a somewhat thicker free anterolateral thigh flap showing not only coverage but also nice contour and texture.

SUMMARY

Though as yet not as popular as in Oriental countries, the anterolateral thigh flap gained widespread acceptance in head and neck cancer surgery. Because of its ease of dissection, together with the other advantages of perforator flaps, it is a very useful adjunct in our armamentarium to treat lower limb defects, in those cases where the thigh panniculus is not too thick and the patient is willing to accept the scar.