Anterolateral Thigh Flap
The first anterolateral thigh (ALT) flap using septocutaneous vessels was described by Song et al in 1984, and its clinical application was popularized by Koshima in 1993. The traits that make the ALT flap particularly suited for reconstruction are its reliable blood supply, minimal donor-site morbidity (even if the motor branch to the vastus lateralis muscle is sacrificed), its thinness, and its long and rather large pedicle. Hence, this flap is often used for reconstructive procedures despite some anatomic variability. Multiple variations of this flap exist, which include the fasciocutaneous flap, myocutaneous flap, adipofascial flap, and chimeric flap.
In recent years, the ALT flap has become well established as the workhorse flap for soft-tissue reconstruction in Asian populations for different regions of the body, such as the head and neck, chest, trunk, and extremities. However, in Western populations, the ALT flap is sometimes hairier and thicker than in Asian populations, which makes this option less popular.
In 2008, Schaverian et al reported on the vascular anatomy of the ALT flap, which was well investigated using 3- and 4-dimensional computed tomographic (CT) angiography and venography. This study further defined the vascular anatomy of the flap that makes flap-thinning procedures possible and more reliable in their clinical application.
Indications
The ALT flap is suitable for most upper limb defects requiring a relatively thin flap. No major artery of the limb is sacrificed, because the pedicle of the ALT flap is the descending or transverse branch of the lateral circumflex femoral artery (LCFA). A cutaneous flap as thin as 5 mm can be harvested after a thinning procedure, and flaps as large as 22 × 32 cm have been used successfully. It is possible to cover exposed bone and tendon simultaneously by using one flap. An ALT adipofascial flap provides defect coverage and gliding surface simultaneously, especially for defects in the distal hand, for which thin soft-tissue coverage is appropriate. Although a split-thickness skin graft is needed for resurfacing the adipofascial layer, reconstruction by an adipofascial flap can be accomplished in one stage. Because of the rich vascularity of the muscle, a musculocutaneous flap can be used for the reconstruction of infected wound after débridement to eliminate the possibility of further infection, while providing coverage of soft-tissue defects. Based on the perforator concept, the ALT flap can achieve more than one defect reconstruction at the same time by means of flap splitting because of the possibility of multiple perforators per flap.
Contraindications
Absolute contraindications to the ALT flap harvest include previous surgery or injury to the upper thigh that compromised the pedicle.
Relative contraindications include morbid obesity, which can make the flap too thick and compromise the vascularity.
Examination/Imaging
Preoperative examinations of the donor site include confirming previous surgery or injury to the upper thigh and recognizing the location of the perforators by using a handheld Doppler flowmeter.
Angiography or MR angiography may be necessary in patients suspected of vascular insufficiency at the recipient site.
Relevant Anatomy
The anterolateral thigh flap is largely supplied by the musculocutaneous (87%) or septocutaneous (13%) perforators of the descending branch of the lateral circumflex femoral artery (LCFA). Less commonly, the blood supply may occasionally be based on the trans-verse branch of the LCFA, in cases where the descending branch is absent or small.
The LCFA branches off the profunda femoris artery proximally and courses obliquely along the intermuscular septum between the rectus femoris and vastus lateralis muscles. Deep within the rectus femoris muscle, the LCFA divides into the ascending, transverse, and descending branches ( Fig. 42.1 ). Thirty-four percent of patients have an extra vessel in the ALT flap from the oblique branch of the LCFA, in the plane between the rectus femoris and the vastus lateralis. The descending branch usually courses inferiorly along the medial border of the vastus lateralis and gives off one or two dominant perforators (with a diameter of 0.3 mm to 0.8 mm) to supply the overlying fat and skin paddle of the thigh. The terminals of these lateral perforators also nourish the lateral femoral cutaneous nerve.
Most commonly (70% of patients), the descending branch does not divide, continues inferiorly along the intermuscular septum, and connects with the lateral superior genicular artery or profunda femoris artery ~ 3–10 cm above the patella.
The diameter of the LCFA ranges from 1.5 to 4 mm, and the average length of the descending branch is 7.6 cm, ranging from 4 cm to 14 cm. The descending branch may be dissected to be longer by ligating the transverse and rectus femoris branches. Routinely, two venae comitantes exist with the descending branch, measuring between 1.5 and 4.5 mm in diameter, which allow venous drainage of the flap.
The sensory nerve (lateral femoral cutaneous nerve) of ALT flap pierces the muscle fascia 10 cm below the inguinal ligament medial to the tensor fasciae latae muscle. The motor nerve innervates the vastus lateralis muscle.
Surgical Technique
Position
Under general anesthesia, the patient is placed in the supine position with the affected arm on a hand table.
A tourniquet is applied to the proximal arm at a pressure of 250 mm Hg.
The lower extremity (donor site) is disinfected and draped well.
Exposure
The ALT flap can be approached using either a medial or lateral incision. More than 50% of perforators are located at the midpoint of the line between the anterior superior iliac spine (ASIS) and the superior lateral border of the patella ( Fig. 42.2 ). The pedicle of the ALT flap courses between the rectus femoris and vastus lateralis muscles.
Pearls
Flap Characteristics
Versatility in design, including multiple variations
Ability to provide sensory innervation (via suprafascial dissection)
Harvest Technique
Ease of harvest with relatively consistent anatomy
Decreased operative time with a two-team approach
Donor-Site Morbidity
Lack of significant donor-site morbidity even if the motor nerve to vastus lateralis is sacrificed
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