**Region:** Lower Extremity # Anterolateral Thigh (ALT) Flap ## Anatomy - Pedicle: descending branch of the lateral femoral circumflex artery (LFCA) with venae comitantes. Caliber approximately 2–3 mm (artery); vein slightly larger. Pedicle length approximately 8 cm (variable; more distal perforator → longer pedicle). Distally communicates with the superior genicular artery above the patella. Venous drainage via venae comitantes accompanying LFCA. - Course: LFCA arises from the proximal profunda femoris artery and divides into ascending, transverse, and descending branches. The descending branch travels deep to rectus femoris in the intermuscular septum between rectus femoris and vastus lateralis, then inferiorly toward the knee; perforators exit along its course to skin/subcutis. - Perforator pattern: majority musculocutaneous (≈80%), coursing through vastus lateralis. Septocutaneous perforators, when present, are more frequent proximally and are preferred for simpler dissection. Primary perforator (“B”) typically at midpoint of line ASIS → lateral patella, most often 1.5 cm posterior to that midpoint and usually within a 3‑cm radius. “A” and “C” perforators are commonly 5 cm proximal and 5 cm distal to B, respectively. If perfusion is a concern, two or more perforators can be harvested; multiple independent skin islands may be designed around separate perforators. - Nerves: lateral femoral cutaneous nerve (LFCN; L2–L3) emerges from deep fascia approximately 10 cm below ASIS and may be included to create a sensate flap. During pedicle mobilization, nerve branches to vastus lateralis lie adjacent to the pedicle and may require division (can be repaired during donor closure). Preserve LFCA branch to rectus femoris and its nerve when possible. - Included tissues: skin, subcutaneous tissue, fascia (fasciocutaneous flap is typical). Can be harvested as myocutaneous (includes vastus lateralis), chimeric (with rectus femoris and/or tensor fascia lata), adipofascial, or superthin (suprafascial dissection and postoperative thinning except for a 2‑cm radius around perforator). Thickness variable — can be excessively thick in obese patients; consider adipofascial flap or alternative donor site if >2 cm subcutaneous fat is problematic (AMT guidance). - Arc of rotation / common variants: flap used as free tissue transfer (scalp → lower extremity) or pedicled for abdominal, perineal, lower extremity defects. Reversed pedicle variant for knee defects possible. Common anatomic variability: absence or paucity of ALT perforators (≈4.3% of thighs may have no ALT perforators in Western populations; when absent, AMT perforators commonly present). ## Dissection Steps 1. Positioning, markings, landmarks. - Position: supine for most indications; toes pointed anteriorly (secure feet together) to facilitate septum identification and consistent landmarks. - Landmarks/markings: draw line connecting anterior superior iliac spine (ASIS) to lateral patella; mark midpoint. Primary (B) perforator typically lies within a 3‑cm radius of midpoint, most commonly 1.5 cm posterior to the midpoint. Mark A and C perforators 5 cm proximal and distal to B, respectively. Draw skin island as a lenticular ellipse skewed so ~1/3 of flap anterior to ASIS–lateral patella axis and ~2/3 posterior. Use handheld Doppler to localize perforator signals pre-incision. 2. Plane, perforator identification. - Initial incision: anterior border of planned flap first. Dissect subfascially (or suprafascially if attempting superthin flap) over rectus femoris toward intermuscular septum between rectus femoris and vastus lateralis. - Identify septum and open it carefully (retract rectus femoris medially). Locate descending branch of LFCA in the septum posterior to rectus femoris. - Use Doppler/visualization to confirm perforator(s). Prefer septocutaneous perforator when available; if musculocutaneous, select a large perforator with favorable intramuscular course. - If suprafascial (superthin) technique chosen, take care to maintain a 2‑cm radius of fat around perforator for perfusion. 3. Pedicle dissection: exposure, control, division; transfer/inset; perfusion checks. - After choosing perforator(s), elevate posterior portion of skin paddle medially toward perforator. - For musculocutaneous perforators: dissect perforator through vastus lateralis muscle to its origin from descending LFCA; take care to avoid traction or thermal injury. - Expose and skeletonize descending branch of LFCA as needed to obtain desired pedicle length. Pedicle can be followed proximally toward profunda femoris to lengthen reach. - Clip/ligate descending branch distal to flap. Preserve LFCA branch to rectus femoris and its nerve. Note nerve branches to vastus lateralis adjacent to pedicle — may be divided and repaired later. - If perforators absent or inadequate: options are (1) explore medial thigh for AMT perforators (arising from rectus femoris branch) or (2) convert to myocutaneous flap by including a portion of vastus lateralis. - Transfer: harvest pedicle on clamps/ligaclips and divide after recipient site preparation. Perform microvascular anastomoses per recipient requirements. Assess perfusion clinically (capillary refill, bleeding edges) and with Doppler as available. If perfusion concerns exist, consider additional perforators or conversion to muscle‑containing flap. 4. Donor-site closure techniques. - Primary closure feasible when width <8 cm; practical upper limits vary by patient habitus (often 8–10 cm). For widths >8–10 cm expect need for skin graft. - “Purse‑stringing” (absorbable running dermal suture 2–0 or 3–0) can reduce skin defect size and may avoid grafting. - Place closed‑suction drain in donor site. If skin graft required, use VAC over an interface dressing. Full‑thickness grafting possible using excess flap skin when available. ## Indications and Contraindications - Indications: - Broad utility: resurfacing of cutaneous and soft‑tissue defects from scalp to lower extremity. - Head and neck reconstruction, scalp reconstruction, phalloplasty, abdominal wall soft‑tissue defect (pedicled or free), perineal reconstruction (pedicled), distal third leg wounds, and cutaneous defects anywhere requiring thin fasciocutaneous tissue (axilla, upper/lower extremity, back, chest). - Need for large skin paddle and two‑team approach favors ALT. - Need for sensate reconstruction: include lateral femoral cutaneous nerve when indicated. - Thin vs bulky: select adipofascial or alternate flap (radial forearm, medial sural artery flap) in obese patients or when thinner coverage required. - Contraindications: - Relative: prior surgery or scarring of donor site that disrupts LFCA or perforators; severe peripheral vascular disease (consider CTA if concern); very thick subcutaneous tissue (>2 cm) may make flap too bulky. - Absolute: absent pedicle anatomy that cannot be remedied by AMT or muscle inclusion (rare) — proceed to alternate donor site. ## Postoperative Care - Monitoring: - Clinical monitoring (skin color, turgor, capillary refill) and handheld Doppler of perforator/arterial flow as standard practice (explicit schedules not specified in supplied texts). - Place closed‑suction drains beneath donor site; leave in place per usual drain output criteria. - Warming: standard care to avoid hypothermia; no specific protocol in provided sources. - Antithrombotic practice: not specified in supplied texts; follow institutional microvascular protocols. - Positioning/splinting: supine positioning pre/intraop; postoperative positioning depends on recipient site. For pedicled thigh use (e.g., knee), plan limb positioning to avoid pedicle kinking. - Mobilization/diet/analgesia: not specified in supplied texts — follow institutional ERAS/microvascular protocols. - Return-to-OR thresholds and time windows: not specifically delineated in supplied materials. The texts emphasize intraoperative decision points (harvest additional perforators or convert to muscle flap when perfusion is inadequate). ## Complications (rates & management) - Reported complications (no rates provided in supplied ALT chapter): - Vascular: venous congestion, arterial insufficiency (thrombosis), partial or total flap loss. - Tissue: infection, fat necrosis. - Donor‑site: inability to close primarily → skin graft requirement; contour deformity; potential functional deficit if extensive vastus lateralis sacrificed (texts note acceptable functional outcomes when vastus lateralis sacrificed with preservation of other quadriceps). - Management algorithms described in sources: - Inadequate perforator/pedicle anatomy at harvest: (1) explore medial thigh for AMT perforators (AMT perforators frequently present when ALT perforators absent); (2) include vastus lateralis muscle (myocutaneous flap) to secure perfusion. - When perfusion concern intraoperatively: harvest two or more perforators if possible or enlarge pedicle dissection. - Donor‑site seroma prevention: closed‑suction drains; limited undermining when closing. - Distal flap tip ischemia risk mitigation: consider superthin technique precautions (preserve 2‑cm radius around perforator) and avoid overly long distal extension; if distal perfusion tenuous intraop, modify design or include additional perforators. - Specific numeric complication frequencies: not reported in the supplied ALT chapter. ## Key Clinical Pearls - Primary perforator (B) location: mark ASIS → lateral patella line; B typically at midpoint and most often 1.5 cm posterior to midpoint (usually within a 3‑cm radius). A and C typically 5 cm proximal and distal to B. - Perforator type: expect musculocutaneous perforators ≈80% of the time; plan for intramuscular dissection through vastus lateralis; if a septocutaneous perforator is present (commonly proximal), prefer it for simpler harvest. - Pedicle facts: LFCA descending branch caliber ≈2–3 mm; pedicle length ≈8 cm (variable, longer when perforator is more distal). - Donor closure planning: design flap width ≤8 cm for routine primary closure; widths >8–10 cm typically require skin grafting. Use purse‑string dermal running suture (2–0 or 3–0 absorbable) to reduce graft size when needed. - Sensation: LFCN can be included for sensate flap; LFCN emerges ≈10 cm below ASIS — identify and include when sensate reconstruction desired. - Intraoperative rescue options: if ALT perforators are absent or diminutive, either (a) explore AMT territory (reciprocal dominance between ALT and AMT perforators) or (b) convert to a myocutaneous flap including vastus lateralis. - Superthin technique precaution: when raising suprafascial/superthin ALT, preserve at least a 2‑cm radius of tissue around perforator for safety.