The Anterolateral Thigh (ALT) Flap: Comprehensive Surgical Guide for Design, Harvest, Donor-Site Closure, and Inset in Partial Glossectomy Reconstruction

Authors: Thomas S. Lee, MD; Eli Gordin, MD; Chris Kandl, MD

Published: 1/20/2026

 

1. INTRODUCTION

The anterolateral thigh (ALT) flap is a workhorse in head and neck reconstruction owing to its long pedicle, adjustable thickness, option for sensate harvest, and low donor-site morbidity. This manuscript accompanies Dr. Lee’s surgical video and follows his operative sequence while integrating pearls from Drs. Gordin and Kandl, as well as evidence from large clinical series and cadaveric studies [2–11]. We provide a practical, literature-aligned, stepwise guide for flap design, harvest, donor-site closure, and inset for partial glossectomy.

 

2. ALT FLAP DESIGN

2.1 Patient Positioning and the AP Line

Position the patient supine with the patella oriented straight upward to avoid external rotation that would shift perforator projection on the skin. A stack of towels can be placed beneath the ipsilateral hip to maintain neutral alignment. Dr. Yu recommends taping the feet together to prevent lateral rotation [3]. 

 

Draw a straight line from the anterior superior iliac spine (ASIS) to the superolateral corner of the patella (the AP line); this serves as the reference axis for perforator prediction [3].  You can also attempt to palpate for the groove between the rectus femoris and vatus lateralis muscles.

 

2.2 ABC Perforator System

In an updated study, Lin, Rabie and Yu described a reproducible map for three reliable perforator sites (A, B, C) along the ASIS–lateral patella line. The B point lies at the midpoint, approximately 1.5 cm lateral to the AP line. The A point is 5 cm proximal to B; the C point is 5 cm distal to B. 

 

In a series of 124 flaps designed without Doppler using this system, intraoperative locations corresponded closely to predictions. Western series demonstrate similar spacing, with the B perforator included in ~87–93% of viable ALT flaps. The A perforator is present in ~49–53% and the C perforator in ~59–63% [3,4]. This supports designing the skin paddle around the B perforator whenever feasible.

 

Figure 1. Right Leg.  AP line connects anterior superior iliac spine and lateral patella.  B point is located at its halfway point and 1.5 – 2cm lateral to the AP line.  There are usually 3 perforators at A, B & C.  A point is 5cm proximal and C point is 5cm distal to the B point. B point perforator is most commonly included in 90% of ALT flaps. Adapted from Reference 3 (Lin et al).

 

2.3 Perforator Types (Septocutaneous vs Musculocutaneous)

In Wei’s experience with 672 ALT flaps, cutaneous vessels were predominantly musculocutaneous (~87.1%) and less commonly septocutaneous (~12.9%). Both courses are reliable when dissected retrograde to the descending branch of the lateral circumflex femoral artery (DB‑LCFA) [2].

 

2.4 Perforator Origin Types (Yu Classification)

Three perforator origin patterns are clinically relevant. Correctly identifying the source vessel is critical to a successful harvest. 

Type I, present in ~90% of cases, features perforators arising from the DB‑LCFA. In the remaining ~10%, variations may complicate ALT use. 

In Type II, the B perforator arises from the transverse branch; in these cases, the flap should be based to include the transverse branch. Type II occurred in ~4%. 

In Type III, the B perforator originates from the profunda femoris. These perforators tend to be of small caliber with short pedicles and are typically unsuitable for free transfer; Yu recommends abandoning the ipsilateral ALT Type III and harvesting from the contralateral thigh instead [4]. In all cases, confirm that the perforator traces back to the DB‑LCFA or the transverse branch and adjust flap design accordingly.

 Figure 2. Three types of anatomic variations of the anterolateral thigh (ALT) flap pedicle. In type I, cutaneous perforators (Pr. A, B, and C) originate from the descending branch (DB). In type II, the cutaneous perforator (Pr. B) originates from the transverse branch (TB). In type III, the cutaneous perforator (Pr. B) originates from the profundus femoris artery (PFA) directly. SFA,superficial femoral artery; LCFA, lateral circumflex femoris artery; AB, ascending branch. From reference 4 (Yu).

 

2.5 Western Thickness Planning

ALT thickness in Western patients correlates with BMI. At the B level, mean thickness is ~13 mm in men and ~20 mm in women; the A level is ~20% thicker than B, and the C level is ~18% thinner than B. Select the C level when thinner tissue is required for intraoral lining, and the A level when greater bulk is desired (e.g., total glossectomy or external contour) [4]. ALTskin flap designed closer to the knee (near C point) will have greater flap vessel reach and may serve as another important decision factor in flap design. 

 

3. HARVEST TECHNIQUE 

3.1 Skin Flap Design & Anterior Incision First

 

• Ensure leg is not externally rotated by placing a stack of towel under ipsilateral hip or by binding the feet together. Identify the B point at the halfway point between ASIS and lateral patella. Design your ALT flap to incorporate the B point.

• A common variation is to shift the B point to 1.5cm – 2cm lateral to the AP line.  While ensuring that the leg is not externally rotated, and palpating for the muscle groove between RF and VL may help you avoid designing your flap too medially. 

 

• Begin with the anterior/medial incision only. Deepen through subcutaneous fat to the glistening fascia lata.

 

 

3.2 Subfascial Dissection 

 

• Enter the subfascial plane ideally directly overlying the rectus femoris. You can aim near the center of the patella with this subfascial incision. This exposes the rectus femoris (RF) and vastus lateralis (VL) while protecting perforators beneath the planned skin paddle [1].

 

3.3 Identifying the Rectus femoris muscle & vastus lateralis muscle

• Look for RF muscle fibers.  RF fibers form a chevron/V toward the ASIS and align with the knee center; VL fibers run more obliquely. If you are directly over the RF–VL septum, the fibers may appear to converge into a V that points toward the knee.

 

• When initially exposing and identifying muscle, it is best to do it either proximal or distal to where the perforators are located to minimize the risk of accidentally injuring them. 
• The septum can also present as a fat pad (in high BMI patients); perforators typically emerge either within the septum (septocutaneous) or more laterally as it travels through the vastus lateralis muscle (musculocutaneous) [1,4].
• Once RF is identified, dissect along its undersurface and medially retract the muscle. Avoid disrupting the RF–VL septum until perforators are clearly identified 

 

• With the RF medially retracted, expose along proximal thigh to identify descending branch and confirm presence of a branch that runs to the undersurface of RF, further confirming correct identification of RF. 

 

 

• Look for descending branch of LCFA. 

 

• Also, look for transverse branch in case you have type II perforators.  

3.3 Perforator-First Retrograde Dissection

 

• Identify the perforator. If musculocutaneous, it must be dissected through the vastus lateralis muscle.  Dissect superficial to perforator vessels under loupe magnification (e.g., 3.5×) and follow the perforator retrograde to the DB‑LCFA, preserving a ~1 cm muscle cuff along its deep aspect to prevent kinking.  Avoid dissecting deep to the perforators until you can clearly see how the vessels travel as the vessel travels in a tortuous fashion.  
• Confirm that it is Type I perforators that originate from descending branch.
• Type II perforators that originates from transverse branch may require longer intramuscular dissection to the transverse branch and corresponding adjustment of the skin paddle to include that branch.
• Type III perforators from the profunda femoris are generally unsuitable for free transfer due to inadequate caliber and pedicle length [1,4].

3.4 DB‑LCFA Pedicle Dissection

 

• Expose the DB‑LCFA on the surface of the vastus intermedius/VL. Dissect perforators proximally to the descending branch and also distally towards skin flap to see where the perforators enter the skin flap.  

• Once the locations where the perforators enter the skin flap have been identified, create a posterior skin flap incision and connect it to deeper soft tissue cuts. Ensure that the perforators are located within the final skin flap design.
• 
• Once retrograde dissection to proximal descending branch has been performed, look for distal run off. Clip it 2–3 mm distal from the perforator takeoff point [1,2].

3.5 Motor Nerve to the Vastus Lateralis (MNVL): 

Motor nerve to the vastus lateralis is in close proximity to the flap vessels and its relationship to the vessels can vary greatly.  Rozen described three problematic relationships between the MNVL and the vascular pedicle: (1) a motor branch traversing the main pedicle; (2) a branch crossing a perforator ; and (3) a branch passing between adjacent perforators—collectively seen in ~28% of thighs [7]. Casey reported that ~7% of clinical cases required major modification due to nerve position [8]. Revenaugh’s cadaveric study confirmed 3–6 primary branches with extensive arborization and variable relationships to the DB‑LCFA and perforators, supporting selective sacrifice when necessary [9]. 

 

Functionally, selective division of a VL motor branch has not been associated with persistent donor weakness; prospective series demonstrate that subjective weakness resolves by approximately 6 months [10]. Similarly, VL muscle harvest has not produced clinically significant long-term dysfunction [10]. Collectively, these studies highlight the importance of prioritizing preservation of flap vasculature; selective sacrifice of the VL motor nerve is acceptable when required, as it is rarely associated with meaningful postoperative donor-site morbidity. With that said, motor branches to other quadriceps muscle should be preserved. 

3.6 Thinning and Shaping

 

Before harvesting the flap, debulk the flap if necessary by tapering subcutaneous fat while preserving the subdermal plexus (leave 1–2 mm) and protecting the perforator. In thick thighs, the perforator can be dissected 1–2 cm distally into the fat to facilitate safer debulking without compromising inflow [5]. Select the A/B/C level to match thickness requirements [4,5].

 

3.7 Flap harvest

Once head & neck site is ready and the neck vessels have been identified, harvest the ALT flap.  The flap vessels are harvested distal to the branch to RF. 

Flap is irrigated with heparinized saline. 

 

4. DONOR-SITE CLOSURE

 

4.1 Primary Closure Feasibility

Primary closure depends on flap width, tissue laxity, BMI, and proximity to the knee; there is no universal cutoff. Yu reported primary closure in ~94% of cases in a Western cohort [4]. 

 

4.2 When Skin Grafting Is Required

Kimata correlated greater morbidity (gait limitation/knee restriction) with grafted donor sites, wider flaps, and designs closer to the knee. Anticipate increased aftercare if grafting is unavoidable and, when feasible, avoid designing the skin paddle close to the knee [11]. In some reconstructions, however, a more distal design may provide additional pedicle reach and can be appropriate depending on recipient site needs. [1]

 

If skin grafting is required, the senior authors (Lee and Kandl) prefer a split-thickness skin graft (STSG) harvested from the ipsilateral thigh, secured with negative-pressure wound therapy (NPWT). A critical step is ensuring an airtight seal at the graft site to prevent loss of vacuum and subsequent Jackson-Pratt (JP) drain leakage. Following maximal primary closure of the leg incision, attention is directed to the graft recipient site. A circumferential, running, buried Vicryl suture is placed through the subdermal layer and secured to the underlying muscular wound bed. The STSG is then applied and the NPWT dressing is maintained for seven days.

 

4.3 Seroma Prevention and Aftercare

Besides using drain suction, Dr. Gordin recommends applying early compression (ACE wrap) [5]. Needle aspiration may be required for seroma. In Hanasono’s prospective series of 220 ALT flaps, reported complications were: seroma 5%, dehiscence 2%, hematoma 1%, and infection 1%—overall low rates [10]. 

 

4.4 Muscle and Nerve Handling

Avoid forced muscle closure that may increase compartment pressures although this is very rare. Re-approximate small VL cuffs when feasible. Expect lateral femoral cutaneous nerve (LFCN) numbness postoperatively; clinically significant donor extremity motor dysfunction is rare [1,10]. 

 

5. INSET FOR PARTIAL GLOSSECTOMY 

 

5.1 Goals

Recreate functional tongue bulk (anticipate ~50% volume loss after radiation therapy) and achieve a watertight closure to protect the neck from salivary contamination and fistula formation. The reconstructed tongue bulk should ideally allow the patient to contact the palate to optimize swallowing function [1].

 

5.2 Pedicle Routing and Protection

 

Before you can inset the flap, you should pass the flap vessels into the neck first. 

 

• Create a tunnel located lingual to the mandible to ensure that flap vessels do not get bitten down by remaining teeth.  The tunnel should be wide enough for at least two fingers,  
• Pass the pedicle using a ½” Penrose drain and confirm non-twisted orientation. After restoring flap perfusion, ensure that neck drains are located away from the pedicle, and maintain gentle vessel loops.  

5.3 Posterior Closure First (Pre-reperfusion)

Complete inset along the deep and posterior aspects of the defect before reperfusion (ideally within 1.5–2 hours of ischemia). This avoids edema-limited visualization and facilitates precise suturing [1].

5.4 Circumdental Suspension

When securing skin flap along the lingual gingiva, use circumdental sutures that wrap around teeth to resist gravitational descent of the skin flap which may lead to salivary fistula [1].  

Dr. Gordin prefers to use PDS sutures for circumdental sutures as it offers greater elasticity and may provide greater watertight closure as tissues swell [5]. 

5.5 Final Checks

Ensure a watertight seal at the flap–tongue–floor-of-mouth junctions and adjacent to remaining native mandible or teeth as these locations are prone to salivary leaks.  

Once vessel anastomosis is complete, confirm adequate Doppler signals.  Drs. Lee and Kandl prefer to use vein doppler couplers (Flow coupler system, Synovis MCA).  

If significant flap swelling is present, lace a bite block for approximately 5 days to prevent dental trauma to native tongue or flap [1].  Dr. Gordin prefers to use a soft bite block with rolled up moistened 4x4s [5].

 

6 Surgeon-Specific Pearls

 

In this section, Dr. Gordin and Dr. Kandl share their insights and their surgical pearls [5,6].

 

Dr. Chris Kandl:

• When designing the ALT flap, Dr. Kandl places a B perforator approximately 2 cm lateral to the AP line.
• He does not routinely use a Doppler to locate perforators and favors the harmonic scalpel for muscle dissection. He has not noticed significant hematoma issues when harmonic scalpel is used. [6]

 

Dr. Eli Gordin:

• While Dr. Gordin uses the classic ASIS–superolateral patella line for orientation, he places greater emphasis on palpating the cleft between the rectus femoris (RF) and vastus lateralis (VL) just lateral to the AP line’s midpoint. In many patients, this intermuscular groove deviates several centimeters from bony landmarks. Prioritizing palpation helps prevent incisions too close to the septum and reduces the risk of disrupting perforators.
• A key teaching point in his practice is avoiding Doppler signals anterior (medial) to the AP line, as these represent rectus perforators rather than true ALT perforators. He frequently observes that residents and new fellows are unaware of this pitfall. In addition, he notes a predictable distribution: septocutaneous perforators are more often found proximal to the midpoint of the line near A point, while musculocutaneous perforators predominately appear distally at C point. 
• For backup options, he highlights both transverse/TFL perforators and, less conventionally, rectus-based perforators that can be traced proximally to the lateral femoral circumflex system. Though disorienting, the rectus-based option is reliable when no VL‑based perforator is present.
• He makes his entire initial skin incision anterior to the septum and over the rectus femoris. This preserves all perforator options while dissection proceeds and ensures commitment to no specific flap design until perforator and oncologic requirements are fully known. He performs a full 360° perforator dissection prior to making any posterior skin incision.
• He similarly prefers subfascial dissection.  Suprafascial perforator identification is possible but requires significantly more time and increases perforator injury risk. In thicker thighs, he prefers first identifying the perforator at the fascia and then dissecting it distally 1–2 cm into the fat to enable safe thinning.
• Immediately after the skin incision, he sharply opens the fascia lata along the incision line using monopolar cautery, disregarding all but the largest rectus perforators. He bevels slightly anteriorly for smaller flaps to avoid encroaching on the septum and then rapidly exposes the underside of the fascia lata. Peeling it laterally allows perforators to come into view without dissecting between RF and VL prematurely. This maneuver preserves muscle-to-muscle tension, improving subfascial visualization.
• Regarding nerve management, Dr. Gordin routinely divides the nerve to vastus lateralis in most cases, except in small flaps, without observing functional deficits. He cautions, however, that branches to vastus intermedius or other quadriceps may travel along the undersurface of the DB‑LCFA; inadvertently dividing these may lead to postoperative weakness. 
• He frequently harvests the VL motor nerve as a graft for facial nerve reconstruction or other applications, preferring it to sural nerve due to lower morbidity.  
• Once the perforator is visualized distally, Dr. Gordin opens the investing fascia of the vastus lateralis to facilitate intramuscular dissection.  He prefers to dissect perforators retrograde rather than seeking a DB‑LCFA branch across the muscle. Perforators may loop in unpredictable paths or travel long intramuscular distances before emerging; therefore, assumptions about straight trajectories are unreliable.
• For proximal exposure, he favors a Gelpi self-retaining retractor to maintain separation between RF and VL without requiring an assistant. He notes that distal DB‑LCFA branches can be used for flow-through purposes when a second flap is required. In addition, he often follows the venae comitantes proximally to a common Y-junction, enabling anastomosis using a single coupler that captures both veins simultaneously.
• For closure, Dr. Gordin mentions that he does not routinely reapproximate the vastus lateralis or suture RF to the fascia lata and notices no major issues postoperatively. He finds no reliable skin flap width threshold predicting primary closure feasibility: some patients tolerate closure of defects up to 18 cm, while others require negative-pressure therapy for as little as 7 cm. Seroma is the complication he encounters most frequently; he manages this with repeated needle aspiration and ACE compression, which he applies immediately postoperatively.
• For flap inset, he places a traction suture through both the flap and the tongue tip, allowing both to be retracted simultaneously. This improves visualization, facilitates suture passage, and distributes flap tissue evenly. He prefers 3‑0 PDS for circumdental suspension due to its elasticity and sealing performance relative to Vicryl. For small or vasospastic vessels, he applies papaverine to the Gelfoam around the pedicle. For a bite block, he prefers a soft bite block fashioned from rolled moistened 4×4 gauze rather than a rigid surgical bite block. [5]

 

7. REFERENCES
8. Lee TS. ALT flap operative technique (user provided).
9. Wei FC, Jain V, Celik N, Chen HC, Chuang DCC, Lin CH. Have we found an ideal soft-tissue flap? Experience with 672 ALT flaps. Plast Reconstr Surg. 2002;109(7):2219–2226.
10. Lin SJ, Rabie A, Yu P. Designing the ALT flap without preoperative Doppler or imaging. J Reconstr Microsurg. 2010;26(1):67–72.
11. Yu P. Characteristics of the ALT flap in a Western population and its application in head and neck reconstruction. Head Neck. 2004;26:759–769.
12. Gordin E. ALT design and harvest pearls (user provided).
13. Kandl C. ALT technique (user provided).
14. Rozen WM, le Roux CM, Ashton MW, Grinsell D. The unfavorable anatomy of VL motor nerves: a cause of donor-site morbidity after ALT harvest. Plast Reconstr Surg. 2009;123:1505–1509.
15. Casey WJ III, Rebecca AM, Smith AA, Craft RO, Hayden RE, Buchel EW. Vastus lateralis motor nerve can adversely affect ALT harvest. Plast Reconstr Surg. 2007;120:196–201.
16. Revenaugh PC, Knott PD, McBride JM, Fritz MA. Motor nerve to the vastus lateralis. Arch Facial Plast Surg. 2012;14:365–368.
17. Hanasono MM, Skoracki RJ, Yu P. Donor-site morbidity after ALT flap harvest in 220 patients (prospective). Plast Reconstr Surg. 2010;125:209–214.
18. Kimata Y, Uchiyama K, Ebihara S, et al. Donor-site complications and morbidity after ALT flap. Plast Reconstr Surg. 2000;106:584–589.