16.2.1 Introduction to the Anterolateral Thigh Flap for Lower Extremity

Following the initial description by Song et al, ¹ the utility of the anterolateral thigh (ALT) flap (Fig. 16‑2) by reconstructive surgeons has increased tremendously. It is now considered the workhorse soft-tissue flap for reconstructive surgeries in various regions of the body. ^{2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8} The relatively consistent anatomy, minimum donor site morbidity, ability to reconstruct simple and composite soft-tissue defects, versatility, long pedicle, and satisfactory caliber of vessels are among the attributes that have led to the popularity of this flap and expanded its utility for both locoregional and free tissue transfer in different body regions including lower extremity reconstruction.

16.2.2 Attributes and Detriments

16.2.3 Flap Components

The ALT flap can be harvested as a cutaneous, fasciocutaneous, or musculocutaneous flap. It can also be harvested as a chimeric flap to include other tissues such as the rectus femoris, tensor fascia lata, or vastus lateralis muscles or even femoral bone, where the ALT flap itself is supplied by a separate perforator or even independent source vessel. The missing tissues at the recipient site will dictate the necessary size, thickness, and components of the ALT flap.

16.2.4 Anatomic Consideration

16.2.5 Anatomic Variations

The pattern and distribution of the vessels supplying the ALT cutaneous territory is variable and failure to understand these anatomic variations can lead to flap vascular compromise. The descending branch of the LCFA commonly arises from the LCFA but can originate from the deep femoral or common femoral arteries. A large-scale systematic review revealed that the majority of perforators to the ALT skin originate from the descending branch of the LCFA in 75 to 100% of cases. Origin from the transverse, ascending, and oblique branches has also been described with wide range of reported frequency. The same study revealed that septocutaneous perforators were present in about 20% of cases and ALT perforators were absent about 2% of the time. ⁹

16.2.6 Patient Positioning

The flap is usually harvested with the patient in a supine position, but can also be harvested with the patient in a semilateral or true lateral position. The lower extremity is circumferentially prepped. Harvesting the flap from the contralateral thigh allows for a two-team approach.

16.2.7 Flap Design

Routinely examine the patient in the preoperative area or in the operating room while awake to determine the location of the septum between the rectus femoris and vastus lateralis muscles. With a straight leg raise test, this septum may be palpated or even potentially visualized in patients with a thin body habitus. Otherwise, a line joining the ASIS and the superolateral border of the patella is marked and will represent the location of the septum, and potential location of septocutaneous perforators. Note that the septum is neither a straight line nor a fixed point, and its location could shift medially or laterally depending on the patient position on the table or if the lower extremity has undergone medial or lateral rotation. All markings will be more reliable with the patient supine and the lower extremity kept in neutral rotation.

A handheld audible Doppler is commonly used next to identify perforator signals, which are concentrated within a 3-cm-diameter circle centered over the midpoint of the septal line. The perforators themselves are most frequently found within the inferolateral quadrant of this circle. Musculocutaneous perforators, of course, will pierce the vastus lateralis muscle posterior to this line. When designing the chosen skin island, it is advisable to encompass more than one perforator, and to preferably shift the flap boundaries slightly posterior to the line joining the ASIS and superolateral patella so as to be able to capture both septocutaneous and musculocutaneous perforators, if present.

In patients with thicker thighs, identification of perforators with the audible Doppler examination can be misleading. Lin et al proposed a very reliable, simple, and accurate model (ABC model) to guide perforator location. ¹⁰ That is, there are usually one to three perforators in the ALT flap territory in predictable locations (A, B, or C). In an average person, perforator B is located near the midpoint, whereas perforators A and C are approximately 5 cm proximal or distal to perforator B. All three perforators are located approximately 1.4 cm lateral to the line joining the ASIS and superolateral patella, but again this can be highly variable.

A longitudinally oriented skin island is designed to incorporate the marked perforators. A skin island up to 35-cm long and 25-cm wide can be harvested on a single dominant perforator, but inclusion of more than one perforator is advisable. This will provide the surgeon the option of using more than one skin island, each based on a separate perforator, or just as a safety factor to prevent inadvertent flap twisting or devascularization.

Variations of the skin island design can place the perforator at centric or eccentric locations. Designing the skin island distally places the chosen perforator at an eccentric position proximally, and thereby increases the effective pedicle length when the flap is based on a proximal pedicle. When using the ALT as a distal-based pedicled flap for coverage of soft-tissue defects about the knee, the perfusion of the flap will be retrograde through communications with the superior lateral genicular system. In these circumstances, designing the skin island proximally on the ALT increases the effective distal pedicle length and enhances the arc of rotation and reach.

16.2.8 Flap Harvest

Suprafascial Approach

The medial flap boundary incision is made first and dissection is carried down to the level of the deep fascia (Fig. 16‑3 and Video 16.1). If additional soft-tissue bulk is necessary, the dissection could be beveled away from the flap to include more subcutaneous fat. The flap is then raised from medial to lateral in a suprafascial plane directly above the fascia lata, using cautery or tenotomy scissor until a skin perforator is identified piercing the fascia. Once perforators of adequate caliber are identified, the fascia is incised and opened medial to the perforators, and the remainder of the septum is opened to expose the descending branch of the LCFA. Dissection is then continued proximally toward the latter’s origin itself from the LCFA. While doing this, multiple motor branches will need to be carefully dissected away from the vascular pedicle and protected to avoid iatrogenic denervation of the thigh musculature, especially when the flap is used as a perforator flap without including part of the vastus lateralis muscle.

Video 16.1 ALT Flap for Lower Extremity Reconstruction.https://www-thieme-de.easyaccess1.lib.cuhk.edu.hk/de/q.htm?p=opn/cs/20/7/12265275-1a6625fc

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The extent of proximal pedicle dissection will be determined by the length and caliber of vessels required. When the ALT is used for locoregional reconstruction, a long pedicle is frequently needed to maximize reach. In these circumstances, the branch to the rectus femoris muscle can be safely divided to obtain an additional effective pedicle length. ^{11 ,​ 12} When the rectus femoris branch is divided, care should be taken to avoid extensive dissection around the rectus femoris muscle distally so the blood supply from minor distal pedicles can be maintained. The rectus femoris branch can also be divided if additional pedicle length is needed when using the ALT for free tissue transfer.

The lateral boundary incision is then made, and suprafascial dissection is continued from lateral to medial till the same perforators identified earlier are visualized. If the course of the perforator(s) is purely septocutaneous, they can easily be dissected down to the source vessel. If the perforators follow an intramuscular course, the usual tedious intramuscular dissection is performed with all muscular branches carefully ligated (muscle branches usually arise from the lateral and posterior surfaces of the perforators). A small cuff of fascia left around the perforator helps prevent pedicle twisting or avulsion, while also being something that can be held safely and maneuvered with forceps. Intramuscular dissection is usually carried out in a retrograde fashion back to the source vessel, but antegrade dissection is also possible.

When the flap is used as a sensate flap, the lateral cutaneous nerve of the thigh is included with the flap. The nerve is identified proximally below the fascial lata and additional length can be obtained by extending the dissection proximally toward the ASIS.

Suprafascial dissection is preferred when a thin flap is required. This allows also for preservation of sensory nerves in the thigh that traverse over the fascia. In addition, preserving the fascia may minimize donor site morbidity such as by preventing muscle herniation.

16.2.9 Pitfalls, Flap Modification, and Tips to Optimize Outcomes

Flap Thinning

When the ALT flap is used for pretibial, dorsum of the foot, ankle, or heel coverage, primary thinning of the flap can be considered especially in patients with excess subcutaneous fat. Thin flaps may have the ability to regain sensation quicker even when transferred as insensate flaps.

Flap thinning is performed while the flap is still being perfused before division of the pedicle to enable continuous monitoring of flap perfusion as well as obtaining adequate hemostasis. Preservation of a 2- to 3-cm soft-tissue cuff around the pedicle entrance into the flap is advised to maintain perfusion. To best accomplish this, the plane between the superficial and deep fat layers is first identified (Fig. 16‑4). The deep fat layer has larger fat lobules, while the superficial layer has smaller and more round lobules, the two usually separated by a thin fascial layer. Flap thinning requires removing the deep fat layer lobules until the superficial layer is reached. Further thinning can actually be performed up to the level of the subdermal plexus; however, flap survival after transfer may be more likely affected by how the flap is inset. Caution must then be observed if tension is excessive, or if a complex defect requires folding of the flap, as viability will be less reliable. Secondary flap thinning is a much easier and safer procedure, and should be a consideration until experience with primary flap thinning is reasonable.

16.2.10 Donor Site Management

Primary closure of the donor site is preferable, but obtaining a flap of adequate size always takes precedence. A skin island with width exceeding 8 to 9 cm at the mid-thigh level may preclude direct donor site closure, which otherwise could result in a thigh compartment syndrome. The donor site may still then be closed primarily at the superior and inferior aspects, but the middle portion may require a split-thickness skin grafting. Using a dermal regeneration template prior to skin grafting or tissue stretching devices will allow time for swelling to subside, which could permit even further or complete closure of the middle portion of the donor site. This may then avoid the risk of skin graft failure, particularly common after a suprafascial flap harvest, and definitely provide a better aesthetic outcome.

Alternatively, synchronous local advancement flaps based on other perforators (e.g., keystone or V-Y flaps) may facilitate complete primary donor site closure, but at the price of additional scarring of the thigh. Preoperative and postoperative thigh tissue expansion has also been described to avoid the need for a skin graft. ^{22 ,​ 23}

Another option, if a wider skin island is needed, is to select a long but narrow longitudinal design. This will require the preoperative identification of at least two major perforators within that design based on that same source vessel, so that the skin paddle can be split into two islands, each based on an individual perforator. The skin islands can then be inset side by side at the recipient site using the “kiss” principle to provide the necessary coverage width, while still allowing primary closure of the donor site. ²⁴

16.2.11 Case Examples

Case 1: Locoregional ALT flap

A 19-year-old woman had a right groin mass excised that proved to be a synovial sarcoma (Fig. 16‑5). Following neoadjuvant radiation, radical sarcoma excision resulted in a right groin defect requiring soft-tissue coverage. This was achieved by transposition of an ipsilateral island ALT flap.

Case 2: ALT Free Tissue Transfer

Following a motorcycle accident, this young man sustained a comminuted right tibia/fibula fracture with extensive soft-tissue degloving. Single vessel runoff remained, making this a Gustilo grade IIIC tibial fracture. Following plate and intramedullary rod fixation, the large defect was covered elsewhere with a latissimus dorsi free muscle flap that was unsuccessful. As a backup option for this now chronic wound, a contralateral ALT free flap was planned (Fig. 16‑6), not only to obtain another huge soft-tissue flap that was needed, but also to have a long pedicle with large caliber vessels that would reach the popliteal vessels outside the zone of injury and permit facile end-to-side microanastomoses. That proved to be successful, allowing limb salvage.

16.2.12 Postoperative Care Protocols

Extreme vigilance and attention to details are required to identify early flap compromise. Studies have shown that the most important factor in salvage of the failing free flap is early identification of any vascular compromise. Even pedicled flaps should undergo serial clinical examination by the surgical/nursing team (every 2–4 hours) starting in the recovery area for the first 24 hours. After the first 24 hours, the frequency of clinical examination varies based on individual cases.

Free flap monitoring typically follows a specified protocol of hourly clinical and, if nothing else is available, audible Doppler examination by a nursing staff specifically trained to care for free flap patients. Familiarity and experience of the nursing staff with the management of free flap patients has enabled care for this subset of patients on a general plastic surgery hospital floor. Admission to an intensive care unit is then rarely needed following lower extremity reconstructions with free flaps unless the general health of the patient and associated medical comorbidities require a higher level of care. Patients are maintained on strict bed rest for 5 days, followed by gradual resumption of lower extremity dangling.

16.2.13 Conclusion

The ALT perforator flap is a versatile flap often used in lower extremity reconstruction. The relatively constant anatomy, adequate pedicle length and caliber of vessels, ability to modify flap components based on the recipient site needs, minimal donor site morbidity, and excellent reported outcomes are among the reasons that have led to widespread adoption and utilization as both a pedicled and as a free flap, for challenges that so commonly present in the lower extremity.

16.3.1 Introduction to the Gracilis Muscle Free Flap

The advent of the realization of the clinical value of microvascular tissue transfers soon followed McLean and Buncke’s ¹ use of the omentum to cover a scalp defect, and Daniel and Taylor’s ² first successful composite tissue transfer. But imperfections of the latter’s groin flap such as anatomical inconsistencies rapidly led to the investigation for more pragmatic donor sites. The rebirth of muscle flaps around the same time frame as an important entity can be traced to Orticochea, ³ who raised large peninsular flaps from the thigh safely without delay maneuvers, with reliability ensured by inclusion of the underlying gracilis muscle. However, without microsurgical capabilities, this had to be a multistaged regional flap for coverage of an exposed ankle bone. ³ Quickly thereafter, the gracilis muscle (Fig. 16.7.) alone proved to be a reliable free flap donor site when Harii et al ⁴ showed its utility for functional restoration of facial paralysis. Musculocutaneous free flap versions that followed were not always completely viable if the skin paddle had a vertical axis, but Yousif et al ⁵ in cadaver studies proved this was because the “true” perforasome of the perforators from the dominant pedicle of the gracilis muscle had a transverse orientation in the upper thigh.

The gracilis muscle indeed deserves the appellation as a “workhorse flap,” as it has been found to solve all conceivable problems within the “skin and its contents,” the realm of the “true” reconstructive surgeon. Often preferable about the upper portion of the lower extremity as a local flap (see Chapter 14B: The Gracilis Local Muscle Flap), the gracilis muscle is extremely versatile also as a free flap. As a musculocutaneous version, the transverse myocutaneous gracilis (TMG) ⁶ or transverse upper gracilis (TUG) ^{5 ,​ 7 ,​ 8} free flap in the appropriate candidate is a secondary option for breast reconstruction. The gracilis muscle can be a dynamic transfer apropos for facial reanimation ^{4 ,​ 8 ,​ 9} or restoration of a myriad of upper extremity functions. ¹⁰ Although its small cross-sectional area limits potential power, ankle dorsiflexion has been achieved. ¹¹ More conventional roles in the lower extremity have been dictated when malleable fill is essential or coverage of small to moderate-sized defects needed. ¹² In the ubiquitous obese patient, this may be the best available thin flap that will not interfere with shoe wear and ambulation.

The gracilis muscle functions as a thigh adductor, knee and hip flexor, and medial hip rotator, ⁸ but only a minimal deficit is noted if absent, so it is considered expendable. ¹³ Potential donor site morbidity is minimal, and the resultant scarring on the medial thigh usually can be well hidden. ^{13 ,​ 14 ,​ 15} It should be reiterated that all these attributes and unlimited roles demand that a complete knowledge of this donor site be mastered by all who use it!

16.3.2 Attributes and Detriments

16.3.3 Anatomical Considerations

The gracilis muscle is found in the more posterior aspect of the medial thigh. It is the most superficial of the muscles of the adductor compartment, extending longitudinally for some 30 cm from its aponeurotic origin at the symphysis pubis and pubic arch to where its tendon inserts as part of the pes anserinus on the medial tibial condyle, where found inferior to the tendon of sartorius and above that of semitendinosus. ^{7 ,​ 8} The width of the muscle may be up to about 7 cm at the level of the major vascular hilum, ¹⁶ then tapers distally toward its long tendon, thereby overall forming a somewhat triangular shape (Fig. 16‑8).

The dominant vascular supply most commonly is considered to be the medial circumflex femoral artery (MCFA), ⁷ although others state it may be the adductor branch or even the first profunda perforator ^{16 ,​ 17} ; however, regardless of what it is, it always ultimately arises from the profunda femoris. ^{16 ,​ 18} The MCFA then courses medially between the adductor longus and magnus muscles before entering the anterolateral undersurface of the gracilis at a point about 10 cm (range: 5–14 cm ¹⁶ ) inferior to the pubic tubercle. ⁵ The artery caliber varies from 1.5 to 3 mm, ⁸ and venae comitantes that are usually larger are always present. The potential pedicle length is about 7 cm. ⁸ As with most muscles, minor pedicles may be found near the origin and insertion. For example, Tremp et al ¹⁹ describe a more proximal pedicle that was a deep branch of the MCFA. Cavadas et al ¹⁷ found a mean of 2.2 distal secondary pedicles that arose from the superficial femoral or descending genicular arteries, with the most proximal of these commonly entering near the midportion of the muscle. Since circulation to the entire muscle is routinely satisfactory via just its dominant pedicle in spite of these minor pedicles, this would be considered a type II muscle using the classification of Mathes and Nahai. ²⁰

Motor innervation of the gracilis muscle is via the anterior branch of the obturator nerve. ⁸ That takes an oblique course between the adductor longus and the magnus muscle before entering the gracilis muscle just superior to its dominant vascular hilum. Following the nerve proximally as far as the obturator foramen will allow harvest up to 13 cm in length. ⁸ After entry into the gracilis muscle, the nerve splits into branches, allowing segmental functional muscle transfers, making this a type I muscle according to the mode of innervation following the schema of Taylor et al. ²¹

16.3.4 Anatomical Variations and Potential Pitfalls

16.3.5 Flap Design

When possible, depending on the lower extremity defect, the patient most easily will be kept in a supine position, with the hip and knee flexed and thigh abducted for the easiest approach to the gracilis muscle. Except in the most obese patient, the course of the adductor longus muscle can be palpated from the pubic tubercle to the medial condyle of the femur. The gracilis muscle will be found posterior to a vertical line drawn between these two points. ²⁸ Since the vascular pedicle to the gracilis muscle enters on the anterolateral border of the muscle, the thigh chosen as the donor site must be determined by the location of the defect and recipient site so that a direct path to the latter without twisting is possible.

If a vertical oriented composite flap is required, the skin paddle should be planned in the upper two-thirds of the thigh below the aforementioned line, centered over the gracilis muscle, and of a width that allows primary donor site closure. For the lower extremity, a transverse elliptical design from the proximal thigh will rarely be necessary. However, if preferred, this should extend no more anteriorly than the hollow overlying the profunda femoris vessels, found just lateral to the anterior border of the adductor longus muscle. ⁶ The upper border of this ellipse should be a few centimeters below the groin crease so as not to distort it, continuing posteriorly to the gluteal crease to almost the ischial tuberosity. The lower border of this flap will correspond to the amount of skin that can be pinched together to also permit direct donor site closure. ⁶

16.3.6 Flap Harvest

For problems confined to the lower extremity, the supine position with the hip and knee flexed and thigh abducted is adequate for harvest and use of the gracilis muscle as a free flap. A bump under the knee will hold the leg steady. Since the gracilis muscle lies almost immediately posterior to the adductor longus muscle, which corresponds to a line drawn from the pubic tubercle to the medial condyle of the femur, a lengthy longitudinal incision just inferior to this line along the medial thigh, or instead a transverse incision paralleling the groin crease as if performing an upper thigh lift, will allow adequate exposure of almost the entire muscle. ¹⁹ However, the scar length can be better minimized by first making a short vertical incision just proximal to the knee joint in the more posterior aspect of the medial thigh (Fig. 16‑9 ²⁹ ; see Video 16.3 ). This approach is extended down through the deep fascia to expose the sartorius muscle fibers that can be seen to run parallel to the femur. If the greater saphenous vein is first seen in the subcutaneous tissues, the dissection should proceed more inferiorly, remembering that the gracilis muscle will be more posterior and just below the sartorius at this level. A circumferential finger dissection below the sartorius muscle permits retrieval of the gracilis tendon much like when grabbing the vas deferens during an inguinal herniorrhaphy.

A Penrose drain wrapped around the gracilis tendon when distracted medially and distally causes movement of the gracilis muscle that can be observed in the proximal thigh. This location is marked on the skin, as well as an arrow above it at about 10 cm distal to the pubic tubercle as a good estimate of where to anticipate the location of the medial circumflex femoral vessels (MCFV), the usual dominant pedicle. If a vertical musculocutaneous flap is planned, the skin paddle should be centered over the muscle now outlined. For the more typical situation just as a muscle flap, only a short longitudinal incision centered about this arrow, once through the deep fascia, allows access to the anterior border of the muscle. With medial muscle retraction, by careful dissection the exact location of the vascular hilum must be identified. The incision can then be extended proximally in a curvilinear fashion upward toward the groin crease to better expose the adductor longus muscle and aponeurotic origin of the gracilis muscle.

The gracilis muscle proximal and distal to the hilum of its vascular pedicle is carefully freed circumferentially from any fascial connections. A Penrose drain distally around the muscle will allow medial retraction for better exposure during lengthening of the vascular pedicle. Likewise, a vessel loop around the pedicle lateral to the hilum facilitates exposure of side branches. The anterior branch of the obturator nerve will be identified just above this point and preserved only if a dynamic muscle transfer is desired. The fascial adhesions of the adductor longus to the adductor magnus are released for several centimeters above and below where the pedicle is seen to go under the former. This allows gentle lateral retraction of the adductor longus muscle, thereby exposing branches to it arising vertically from the MCFV. These are carefully ligated individually, which upon doing so better defines the further course of the MCFV. More lateral dissection ceases when the pedicle is considered long enough. If an extended pedicle is required, the adductor longus muscle is freed by a lateral subfascial approach and retracted medially to expose the MCFV origin from the profunda femoris (see sections on “Anatomical Variations” for details).

Once pedicle dissection is completed, the proximal incision is extended distally only until blunt finger dissection around the more distal unexposed muscle is completely possible via the two incisions that have been made. Often this will expose a prominent secondary pedicle that will have to be ligated. A long silk suture is sewn to the tendon with its free ends then brought with a long gooseneck clamp through the distal subfascial tunnel so created into the proximal incision. The tendon is divided distally, and traction on the suture will bring the tendon and distal muscle into the proximal wound. Next, the aponeurotic origin at a level just below the symphysis pubis is taken down to create an island flap, only attached to the thigh by its vascular pedicle. When ready, the vascular pedicle is divided, and the flap transferred to whatever is the recipient site.

16.3.7 Postoperative Care Protocols

The gracilis muscle free flap requires no unique protocols for management. Institutional policies for monitoring, dressings, and subsequent ambulation should be followed as is the routine.

16.3.8 Conclusion

The gracilis muscle as a free flap for the lower extremity is adequate for small to moderately sized defects (Fig. 16‑10). Minimal bulk allows coverage of the foot and ankle (Fig. 16‑11), where especially after muscle atrophy use of shoe wear and subsequently ambulation will not be impeded. Since extremely malleable, fill or three-dimensional insetting is an asset. There is a limited role as a dynamic flap for the lower extremity. The anatomy and vascular supply of this muscle is consistent to allow an expeditious harvest. However, in the presence of severe atherosclerotic peripheral vascular disease, the arterial orifice may be extremely difficult to visualize or allow passage of sutures, so an alternative donor site should be considered for this subset of patients.

16.4.1 Introduction to the Versatile Latissimus Dorsi Muscle Free Flap

In the search for a more reliable method to ensure viability of a random-patterned axillary skin flap used for replacement of the chest skin after mastectomy, Tansini ¹ resorted to his own cadaver dissections to conclude that keeping the underlying latissimus dorsi (LD) muscle (Fig. 16.12) attached would be the answer. And so a “new procedure,” ¹ was born, the LD musculocutaneous flap as a local flap. But not until Olivari ² some seven decades later was this rediscovered. The near synchronous introduction of microvascular surgery led to the quest for more reliable donor sites, so as a logical progression, Maxwell et al ³ realized that this quite robust island flap with its large caliber and lengthy pedicle would also make an ideal free flap.

The function of the LD muscle is to extend, medially rotate, and adduct the humerus, ^{4 ,​ 5 ,​} s. Literatur as well as stabilize the pelvis during locomotion and hold the inferior angle of the scapula against the chest wall. ⁴ The synergistic action of some six other muscles in the shoulder girdle does not replace all these functions, as Lee and Mun ⁷ in a systematic review have shown that there is an overall impairment such as weakness in 40% of patients. However, most have little difficulties in daily life or work activities, ^{7 ,​ 8} a finding that explains why this muscle is even considered by Zenn and Jones ⁹ to be “the most expendable muscle in the body.” The numerous attributes of this large muscle explain its long-standing and widespread use as a local flap for the head and neck, breast, thorax, and upper arm. ^{6 ,​ 9} The very same characteristics have made it an ideal free flap for use throughout the lower extremity as well. The fact that Bartlett et al ⁵ in their cadaver dissections found no pedicle occlusive atherosclerosis makes the LD muscle a first consideration instead of using lower extremity free flap donor sites especially in the elderly or those with peripheral vascular disease, even though a different body region must be violated. To quote Serafin, ⁴ for all patients needing a free flap, the LD muscle is the “gold standard of donor composite tissue because of its dependability and applicability.” And so it is.