In 1984, Song and coworkers described the thigh as a donor site for three new flaps, which they raised from its posterior, anteromedial, and anterolateral aspect [509]. Of these three flaps, the anterolateral thigh flap became most popular, especially in head and neck reconstruction. Although originally described as a fasciocutaneous flap which is nourished by a septocutaneous perforator of the descending branch of the lateral circumflex femoral artery, the design of the flap significantly depends on the course and location of the cutaneous vessels, the anatomy of which can vary considerably. Because of the fact that the perforator often takes its course through the vastus lateralis muscle instead of running strictly along the intermuscular septum, parts of the vastus lateralis muscle have to be included into the flap in these cases. Besides the possibility of raising large skin paddles on a single perforating vessel, the vastus lateralis muscle can be transferred as a muscle-only flap, being safely perfused by the descending branch. Thus, a number of flap raising possibilities arise at the anterolateral thigh, offering a wide spectrum of flaps to be harvested. In one of the first large clinical series, Zhou et al. described successful transplantation of this flap in 32 patients, most of them having defects in the region of the face and scalp [635]. Based on a single perforator, a flap design was described reaching in length from the distal end of the tensor fasciae latae muscle to a level 7 cm above the patella and in width from the medial edge of the rectus femoris muscle to the lateral intermuscular septum. According to Koshima and coworkers, who reported on 22 reconstructions of head and neck defects, the flaps can have up to 25 cm in length and 18 cm in width [288]. Two years later, the same author combined the anterolateral thigh flap with neighboring skin-, myocutaneous-, and bone flaps using the lateral circumflex femoral system to treat massive composite defects of the head and neck, performing an additional anastomosis at the distal end of the descending branch [299]. In 1995, the usefulness of the anterolateral thigh flap to cover defects in the lower extremity was demonstrated by Pribaz and coworkers, especially because of the possibility to harvest and transfer the flap in epidural anesthesia [420]. An important variation of designing the anterolateral thigh flap was introduced by Kimura et al. in 1996, who performed a primary radical thinning procedure, only leaving a small cuff of fatty tissue around the perforator [281]. With this procedure, ultrathin flaps could be created, being very useful to cover superficial skin defects [73, 281, 584, 620]. To improve intraoral defect coverage, Wolff et al. performed additionally de-epithelialization of the thinned flaps to create a mucosa-like flap surface [606]. In the following years, the exceptional wide spectrum of indications and the high reliability of the flap were reported especially from authors of the Asian countries. In 2002, Wei et al. published a series of 672 anterolateral thigh flaps with a total flap failure in only 12 patients [584]. An even larger number of 1284 patients were presented by Gedebou and Wei in the same year, who described the anterolateral thigh flap as one of the most useful soft tissue flaps, especially in head and neck reconstruction [162].

The vastus lateralis muscle first was used as a pedicled regional flap to treat trochanteric pressure sores [59, 124, 208, 371] and to repair defects at the gluteal region [1] and knee [522]. In 1987, Drimmer and Krasna described myocutaneous vastus lateralis flaps in four patients to treat decubiti at the gluteal region [127]; later, Rojviroy et al. used this pedicled myocutaneous flap to cover trochanteric pressure in paraplegic patients [444]. The first microsurgical transfer of the vastus lateralis muscle flap to the oral cavity was reported by Wolff in 1992 [598], who covered intraoral defects using myofascial and myocutaneous flaps. In further clinical series, the same author described the usefulness of the muscle in combination with one or more skin paddles for reconstruction in the head and neck including the skull base and perforating defects of the cheek [591, 602, 605, 606]. Because muscle flap raising can be carried out independently from cutaneous vessels, flat and fascial covered flaps can be created from the distal half of the vastus lateralis, giving the possibility to obtain vascular pedicles of up to 15 cm.

The vastus lateralis represents the largest portion of the quadriceps femoris muscle and is localized between the vastus intermedius, biceps, and rectus femoris muscle. Its origin is from the intertrochanteric line, the greater trochanter, gluteal tuberosity, and the lateral intermuscular septum. Together with the other muscles of the quadriceps group, its tendon builds the patellar ligament and thus is a strong extensor of the leg [445, 588]. Together with the gluteus maximus muscle, the vastus lateralis forms the “vastogluteal muscle sling,” leading to an extension, external rotation, and adduction of the leg [573]. The muscle, which has a dimension of about 10 × 25 cm, is innervated by motor branches of the femoral nerve. This nerve enters the muscle at its medial border in the proximal and intermedial segments and follows the course of the main dominant vascular pedicle. The vascular supply of the vastus lateralis muscle comes from the descending branch of the lateral circumflex femoral artery and its two venae comitantes, having a diameter of 1.5–2.5 mm (artery) and 1.8–3.3 mm (veins) [598]. According to Mathes and Nahai, the muscle has type I pattern of circulation, providing perfusion of the whole muscle from this dominant vascular pedicle [346, 347]. Additional minor pedicles reach the muscle far proximally (transverse branch of the lateral circumflex femoral artery) and distally (lateral superior genicular artery), having no significance for microvascular transfer. After its spring off from the lateral circumflex femoral artery, the descending branch reaches the medial rim of the vastus lateralis muscle in its proximal segment and courses distally to communicate with the superior genicular artery. Because the whole muscle is nourished by side branches of the artery, muscle flaps can be raised from each portion of the vastus lateralis. The vascular pedicle can easily be exposed in the triangle which is built by the tensor fasciae latae, vastus lateralis, and rectus femoris muscle in the proximal third of the thigh. Here, the pedicle has a length of 6–8 cm before entering the vastus lateralis muscle. When used as a rotation flap, the proximally based muscle can reach the trochanteric, gluteal, perineal, and lower abdominal region. As a distally based flap, the lower third of the muscle which is supplied by the distal minor pedicle can be used for defect coverage around the knee [522].

In addition to providing blood supply to the vastus lateralis muscle, the descending branch also gives off myo- or septocutaneous branches, providing the anatomical basis for the myocutaneous vastus lateralis- or septocutaneous anterolateral thigh flap. These flaps, which can be considered as one entity, only differ from each other in the amount of muscle tissue that is included during flap raising. Depending on the course of the cutaneous vessels, a portion of the medial edge of the vastus lateralis muscle has to be removed to form a protecting cuff around myocutaneously running vessels. According to the results of previous anatomical investigations, the dominant cutaneous vessel of the anterolateral thigh was found to have a myocutaneous course in 80–90%. Since the myocutaneous vessel traverses the muscle close to its medial edge, a small cuff of muscle must be included, however, the function of the vastus lateralis can be completely preserved. For extended and deep defects, larger portions of the vastus lateralis muscle, having the same size as the skin paddle, can be harvested, so that voluminous myocutaneous vastus lateralis flaps are created. In only 10–20%, the dominant cutaneous vessel is having a direct course to the skin, running along the lateral intermuscular septum between the rectus femoris and vastus lateralis muscle and piercing the fascia lata without traversing through the vastus lateralis muscle. These anterolateral thigh flaps are raised without any muscle tissue and thus are offering thin and pliable skin paddles, being well suited for reconstructions in the head and neck area including the oral cavity.

In a number of anatomical investigations and clinical series, the vascular anatomy of the anterolateral thigh was found to be variable, making it necessary always first to expose the cutaneous vessel before the location of the skin paddle can be determined definitively. The dominant cutaneous vessel can be found within a 4 cm radius at the midpoint of a line between the anterior superior iliac spine and the lateral border of the patella in nearly all cases [346, 598]. To facilitate exposure of the cutaneous perforator, preoperative mapping using an audible Doppler is generally recommended [316, 318]. Although the definite course of this dominant cutaneous vessel can only be explored during flap raising, a myocutaneous pattern can be expected if the Doppler signal is detected not directly over the palpable groove between the rectus and vastus lateralis muscle, but 2–4 cm lateral to the septum above the medial portion of the muscle. Once the exact location of the perforator is defined, the skin paddle can be outlined over the middle third of the lateral thigh between the medial border of the rectus femoris and the lateral border of the vastus lateralis muscle, having a dimension of up to 12 × 30 cm [346]. Depending on the exact location of the main cutaneous perforator, the length of the vascular pedicle varies, being 12 cm in average [497]. Apart from this main perforator, the descending branch is giving off 1–3 additional cutaneous branches, reaching the skin more distally to the main perforator. Whereas the most distally located of these additional vessels are not reliable for skin perfusion, a second perforator can be found in about 90% of all cases 4–9 cm distal to the main perforator, making it possible to build a second independent skin paddle. Like the dominant perforator, this additional cutaneous vessel is having a myocutaneous course in 80–90%, piercing the muscle in a distance of 2–5 cm from its medial rim. The variations of the course of the cutaneous perforators were described in detail by Sieh, who found vertical musculocutaneous perforators in 57% and horizontal myocutaneous perforators in 27%, whereas vertical septocutaneous perforators were found only in 11% and horizontal septocutaneous perforators in 5% of all of their 36 clinical cases [497]. The length of the cutaneous perforating vessels varied between 3.6 and 7.7 cm. In his more than 100 clinical cases, Lee observed a single perforator in 18%, double perforators in 54%, and triple perforators in 28%, most of them originating from the descending branch (70%), whereas the transverse branch was the origin in 9% and both the descending and transverse branch in 22% [314].

Sensory innervation of the perforator flap skin paddle can be established by anastomozing branches of the lateral cutaneous femoral nerve [598]; Ribuffo et al. described, in an anatomical and clinical study, that a superior nerve branch innervates 25%, whereas a medial branch innervates 60% of the vascular territory, so that a selection can be made according to the location and size of the skin paddle without sacrifice of the whole lateral cutaneous femoral nerve [433].

The vascular anatomy of the cutaneous perforators of the lateral thigh was found to give a suitable basis for primary flap thinning procedures, which were first described by Kimura and Satoh in 1996 [281]. In their first five cases, they removed the subcutaneous fatty tissue uniformly from the whole flap except for the region around the perforator, obtaining a flap thickness of only 3–4 mm.

Further experience with primary thinning has shown that the radical removal of fatty tissue does not impair flap perfusion, if the subdermal vascular plexus is preserved and attention is paid to the vascular territory of the corresponding flap vessels [290]. Although Ross and coworkers found a higher complication rate in their clinical series [447] and Alkureishi et al. could experimentally find a reduced dye perfusion of the thinned flaps [6], the literature generally reports low complication rates [6, 172, 290, 584, 606]. All authors agree, however, that flap thinning must be performed with a high degree of technical skill and exact knowledge of the vascular anatomy. A prerequisite for successful thinning is the preservation of the subdermal vascular plexus, which means that the minimal flap thickness should not be less than 3–4 mm. Under these conditions, the size of the vascular territory of a thinned flap corresponds to conventional flaps [290, 393, 584]. Whereas Kimura et al. (1996) emphasized that the vessel anatomy of the anterolateral thigh flap is especially suited for flap thinning [281], if the perforator courses directly to the skin, other authors performed additional dissection through the vastus lateralis muscle in the case of a myocutaneous vessel course to obtain thinned flaps [65, 162, 584, 606] Using this technique it is possible to raise voluminous, extensive flaps as well as very thin small flaps from the same donor region.

Since its first description by Song in 1984 [509], the anterolateral thigh has developed as one of the most preferred donor sites for soft tissue reconstruction, especially in the head and neck area. With a failure rate of less than 2%, Wei and coworkers performed reconstruction in 660 cases, most of them having defects in the head and neck region. Irrespective of whether the skin vessels were septo- or myocutaneous, they could raise versatile soft tissue flaps in which thickness and volume could be adjusted to the extent of the defect [584]. Similar results were provided by Xu and coworkers, who performed a retrospective analysis of almost 900 cases [616]. According to their experience, the anterolateral thigh could replace most of the other donor sites for soft tissue free flaps. Besides the exceptional great experience of Wei’s group, similar results are reported by a number of other authors, describing success rates of about 95% with a wide indicational spectrum, reaching from perforator-based ultrathin skin flaps to myocutaneous vastus lateralis and extensive chimeric flaps, which include parts of the surrounding muscles and even segments of the iliac crest [299]. The donor site can be closed primarily, if the width of the flap does not exceed about 8 cm, and there are no significant functional or aesthetic impairments at the lower leg even after harvesting a large portion of the vastus lateralis muscle.

In a systematic review, 42 relevant articles describing the donor site morbidity after harvesting the ALT flap were analyzed by Collins and coworkers, who found a paresthesia of the lateral thigh as the most common complication in 24%, musculoskeletal dysfunction and hypertrophic scars in about 5%, and pain, seroma, and infection in 2–3%. Very rarely severe complications like a compartment syndrome and partial muscle necrosis were described [105]. However, when raising flaps from the anterolateral thigh, the surgeon must be aware of possible variations in vascular anatomy. Besides the variability of the course and location of the main cutaneous perforator, the absence of any cutaneous branches is possible in seldom cases [288, 308, 584, 591] and was described to occur in up to 5.4% [277]. Although the branching pattern of the skin vessels in a series of 74 clinical cases could be classified into eight categories, no variation was found making flap raising impossible. In this series, 2.3 perforators per case were found, 82% of them having a myocutaneous course, branching off at different levels from the descending branch, from the lateral circumflex femoral artery, from the transverse branch, or directly from the profunda femoris artery [17, 277]. Because the veins which accompany the nutrient artery can show different backflow strength, venous return should be checked before anastomosis. The necessity of a second venous anastomosis in ALT flaps was investigated by Chen and coworkers, who found a higher number of revisions in flaps with only one venous anastomosis, but no difference in flap survival due to successful revisions [87]. In a clinical study of 115 flap raising procedures at the anterolateral thigh, the descending branch was found to be absent in 22.6%, being replaced by the medial descending branch or other strong muscle branches [17]. Although in this study the anatomical course of the descending branch could be classified into six different categories, flap elevation was possible in all cases because at least one cutaneous perforator was observed regularly. For intraoral defect coverage, the thickness of the flap can be disadvantageous, especially in myocutaneous flaps carrying a large portion of muscle tissue. In these cases, muscle or fatty tissue has to be primarily removed without injuring the cutaneous vessel, but these thinning procedures should only be carried out by experienced surgeons having an exact knowledge of the vascular anatomy. Because of the neurogenic muscle atrophy and secondary shrinkage, purely muscular flaps have only a limited indication for intraoral soft tissue replacement [595]. The width of the skin paddle in myocutaneous flaps is limited to about 8–10 cm; in males, sometimes a strong hair growth can be observed at the lateral thigh. Apart from some loss of sensation, the donor site morbidity is low, but can increase when wider flaps needing a split thickness skin graft for closure of the donor site or flaps including significant parts of the vastus lateralis muscle have been harvested [278].