**Region:** Lower Extremity # Posterior Thigh Flap ## Anatomy - Pedicle: descending branch of the inferior gluteal artery (axial fasciocutaneous pedicle). Mean arterial caliber reported as 1.33 mm (gluteal-thigh literature). The descending branch: - Origin: typically from the inferior gluteal artery; less than 10% of cases it may arise from the profunda femoris, medial circumflex femoral, or lateral circumflex femoral. - Course: leaves pelvis below piriformis → runs deep to gluteus maximus → exits into posterior thigh at the midpoint of the inferior gluteal border (midpoint between greater trochanter and ischial tuberosity) → courses subfascially in the midline of the posterior thigh, staying above and between biceps femoris (lateral) and semitendinosus (medial) toward the knee. - Venae comitantes: paired venous channels accompany the artery and drain into the deep venous system; preservation of venous drainage (skin bridge or subcutaneous base) is important to prevent congestion. - Perforator pattern: - Multiple cutaneous perforators along the course of the descending branch supply skin/subcutaneous tissues. - Perforators are encountered throughout the midline posterior thigh; pedicle is often visible in the mid- and distal thirds during dissection. - A superficial plexus of gluteal perforators also contributes to posterior thigh vascularity (not typically the main pedicle for this flap). - Flap dimensions reported: can be designed up to ~12–15 cm width and up to ~30 cm length; practically, primary donor-site closure usually feasible up to approximately 10–12 cm width depending on body habitus; flap may be extended to just above the popliteal fossa (numbers per source). - Nerves: - Posterior femoral cutaneous nerve (posterior cutaneous nerve of the thigh) travels in the same connective tissue sheath as the descending branch in approximately 72% of cases → allows harvest of a sensate flap when nerve included. - Sciatic nerve lies superior and lateral to the dissection field and must be identified and preserved. - Pudendal vessels lie superior/medial to the ischial tuberosity and should be respected during inset in perineal reconstruction. - Included tissues and variants: - Standard flap: skin, subcutaneous tissue, fascia (fasciocutaneous). - Can be islanded or harvested with a proximal skin/subcutaneous base left intact to enhance venous outflow. - May include a portion of gluteus maximus (myocutaneous variant) when additional bulk or arc is required (take inferior portion of gluteus maximus to level of piriformis if needed). - Can be deepithelialized proximally or distally to fill dead space (e.g., pelvic outlet, ischial pressure-sore padding) or tunneled subcutaneously for perineal defects. - Arc of rotation: reliably reaches ischial tuberosity, perineum (vulvar/perianal/posterior vaginal), sacrum, lateral hip/thigh; can be tunneled subcutaneously to anterior/perineal defects. - Common anatomic note: descending branch typically exits under gluteus maximus at the midpoint of the inferior gluteal border; pedicle lies between hamstring muscles. ## Dissection Steps 1. Positioning, markings, landmarks. - Position: prone for harvest (or lithotomy if simultaneous inset to anterior/perineal defect is planned). Mark gluteal crease; identify midpoint between greater trochanter and ischial tuberosity (locates pedicle exit). Draw axis from that exit point to center of popliteal fossa to mark flap long axis. - Skin paddle sizing: can extend to just above popliteal fossa; practical width for primary closure ~10–12 cm (wider flaps may require grafting). Use handheld Doppler to localize descending branch/perforators pre- and intraoperatively. 2. Plane and perforator identification. - Elevation plane: subfascial (deep to deep fascia/fascia lata) is safest and recommended. Avoid suprafascial dissection which risks injuring the pedicle. - Perforator identification: start distally and elevate the flap from distal → proximal in the subfascial plane, identifying cutaneous perforators and following toward the descending branch. Use Doppler to confirm pedicle location if needed. - Preserve medial or lateral skin bridges or a proximal subcutaneous base if venous drainage is a concern. 3. Pedicle dissection: exposure, control, division; transfer/inset; perfusion checks. - Dissection approach: elevate flap from distal to proximal. As you approach the mid-thigh, the pedicle is typically visualized in the mid- to distal-third. Continue dissection proximally to the inferior margin of gluteus maximus to include the pedicle. - Control: divide and ligate deep femoral perforators encountered during proximal elevation. If additional length is required, the inferior portion of gluteus maximus may be detached to follow the descending branch more proximally toward the inferior gluteal artery (convert to a gluteal-thigh flap). - Division: if an island pedicle is desired, make the proximal incision below the gluteal crease and finish pedicle dissection; otherwise leave a skin/subcutaneous base proximally for venous drainage. - Transfer/inset: rotate or transpose flap into defect (may be tunneled subcutaneously for perineal defects). Deepithelialize proximal or distal ends when bulk is required to fill dead space (e.g., pelvic outlet, ischial pad). - Perfusion checks: intraoperative visual assessment of flap color, capillary refill; use of Doppler to confirm arterial signal on pedicle/perforators. Ensure no twisting or kinking of pedicle during inset. 4. Donor-site closure techniques. - Suprafascial undermining medially and laterally as needed to allow tension-free layered linear closure over one or more closed-suction drains. - If primary closure is not tension-free, plan for split-thickness skin grafting. - Place at least one closed-suction drain beneath the flap/donor site to prevent seroma. ## Indications and Contraindications - Indications: - Ischial pressure sore coverage. - Perineal reconstruction (vulvar, perianal, posterior/lateral vaginal defects). - Sacral defects, lateral thigh/hip reconstruction. - Pelvic outlet filling after abdominoperineal resection (flap can be tunneled to perineum). - Sensate reconstruction when posterior femoral cutaneous nerve included. - Size and tissue considerations: - Flap can be designed up to ~12–15 cm wide and up to ~30 cm long (reported ranges); practical primary closure typically achievable up to ~10–12 cm width; larger defects may require graft closure of donor site. - Choose fasciocutaneous versus myocutaneous variant depending on need for bulk/padding. - Contraindications / relative limitations: - Previous surgery that transected the descending branch or inferior gluteal vasculature (e.g., prior large gluteus-maximus rotation flap, inferior gluteal artery perforator flap) may preclude use. - Obesity: thick posterior thigh makes rotation difficult without pedicle skeletonization and increases technical difficulty. - Ambulatory patients: extensive release of gluteus maximus should be avoided (limits functional morbidity); myocutaneous harvest of substantial gluteus maximus is not preferred in ambulatory patients. ## Postoperative Care - Monitoring and drains: - Place closed-suction drains beneath flap and donor site; remove per standard drain output criteria (not further specified in source). - Clinical monitoring: serial flap checks for color, capillary refill, turgor; handheld Doppler may be used to confirm pedicle flow. - Positioning and pressure management: - For ischial/perineal reconstructions, strict offloading of the reconstructed area (wheelchair mapping and pressure-redistribution plan) is critical before allowing prolonged sitting; counsel patients with spinal cord injury accordingly. - If flap was harvested prone and inset requires anterior access, reposition patient supine for inset as dictated by operative plan. - Mobilization and wound care: - Supine/lithotomy positioning may be used intraoperatively for combined procedures; postoperative ambulation dependent on reconstruction and surgeon preference (not specified numerically in sources). - Maintain drains until acceptable output; wound care per standard layered closure protocols. - Analgesia, antithrombotic practice: - Specific regimen not detailed in the available sources; follow institutional protocols. - Return-to-OR thresholds and time windows: - Not specified in source texts. Use standard reconstructive thresholds for suspected arterial insufficiency, venous congestion, or expanding hematoma (immediate re-exploration for compromised perfusion per institutional practice). ## Complications (rates & management) - Reported complication rates: numeric flap-specific complication rates were not provided in the posterior-thigh–specific sources reviewed. - Typical complications and their intraoperative / postoperative management as described in source material: - Venous congestion / inadequate venous drainage: - Preventive measures: preserve a proximal skin/subcutaneous bridge when possible; avoid excessive skeletonization without planning for venous outflow. - Management options in text: leaving broader base for venous drainage rather than complete islanding when venous return is a concern. - Pedicle injury: - Prevention: perform dissection in subfascial plane; use Doppler to localize pedicle; avoid suprafascial dissection. - Management: if pedicle transection occurs, consider alternative reconstructive options (not further detailed in sources). - Donor-site seroma/hematoma: - Prevention/management: place closed-suction drain(s) beneath flap and donor site; layered closure. - Wound closure tension / dehiscence: - Prevention: limit flap width based on pinch test/skin laxity; undersurface undermining as needed; if tension anticipated, plan skin grafting. - Ischial pressure-sore recurrence / flap breakdown: - Prevention: ensure adequate padding (deepithelialized distal bulk), optimize offloading and wheelchair mapping; close coordination with rehabilitation team. - Donor-site morbidity: - Functional morbidity is limited compared with muscular flaps; if gluteus maximus is partially harvested, ambulatory patients may be affected—avoid extensive gluteus maximus release in ambulatory patients. - Management: standard wound care, possible skin grafting if primary closure fails. ## Key Clinical Pearls - Preop marking: locate pedicle exit point at midpoint between greater trochanter and ischial tuberosity; draw axis to the center of the popliteal fossa. Use handheld Doppler to confirm perforators/pedicle. - Elevation plane: perform the dissection in the subfascial plane (deep to fascia lata) — suprafascial dissection risks pedicle injury. - Direction of harvest: elevate flap from distal → proximal; the pedicle is commonly visualized in the mid- to distal-third of the posterior thigh. - Venous drainage: if venous outflow is a concern, preserve a proximal skin/subcutaneous bridge rather than creating an islanded flap; medial or lateral skin bridges help venous drainage. - Sensate flap: include the posterior femoral cutaneous nerve when possible — it is within the pedicle sheath in ~72% of cases. - Bulk and dead-space management: deepithelialize distal and/or proximal limbs of the flap to provide padding for ischial defects or to fill pelvic outlets. - Pedicle extension: if additional length is required, follow the descending branch proximally into the inferior gluteal artery (convert to a gluteal–thigh flap) but avoid extensive release of gluteus maximus in ambulatory patients. - Donor-site closure: plan flap width with a pinch test; practical primary closure usually possible up to ~10–12 cm width (generally up to ~12–15 cm reported in literature); place closed-suction drains and limit undermining to protect lymphatics.