**Region:** Lower Extremity # Gastrocnemius Flap ## Anatomy - Pedicle: named artery (typical diameter/length if present), venae comitantes; course from origin to flap/skin paddle; perforator pattern (number, location, intramuscular vs septocutaneous), choke vessels/adjacent angiosomes. - Each head is supplied by a single dominant pedicle from the popliteal artery: the medial sural artery for the medial head and the lateral sural artery for the lateral head (type I Mathes & Nahai) (Mericli; Shokrollahi). - Reported pedicle measurements (reported values vary by series): medial sural artery length reported as 5.1 cm (average) and lateral sural artery 4.8 cm (Mericli). Other series report a medial sural pedicle length ≈ 2.6 cm with arterial/venous caliber ≈ 1.4 mm (Shokrollahi). Each artery runs with paired venae comitantes that drain to the popliteal system (Mericli; Shokrollahi). - Course: popliteal artery → medial/lateral sural arteries → deep surface of gastrocnemius head; vessels enter on deep surface with accompanying motor branches (Mericli). - Skin supply: musculocutaneous perforators are concentrated in the proximal part of the muscle and provide the principal cutaneous blood supply; these perforators are more numerous proximally and are mainly musculocutaneous (not large septocutaneous) — explains the preference for muscle-only flap with split-thickness grafting or very proximal skin paddles when a myocutaneous flap is attempted (Mericli; Shokrollahi). - Choke/linking vessels: communications exist between the medial sural territory and adjacent cutaneous vasculature (posteriorly > anteriorly); distal cutaneous supply is tenuous (Mericli). - Nerves: sensory and motor branches relevant to flap harvest and sensate reconstruction. - Motor: medial and lateral sural motor branches (branches of the tibial nerve) enter the deep surface of each head with the sural vascular pedicle; nerves are typically ≈ 5 cm in length to the muscle entry point and can be divided when raising a pedicled flap to avoid contraction (Mericli). - Sensory: sural nerve courses in the septum between heads with the lesser (short) saphenous vein — identify and preserve when possible (Shokrollahi; Mericli). - Important adjacent nerve: common peroneal nerve runs posterior/medial to the biceps femoris and crosses near the lateral head origin — at risk during lateral head dissection; avoid injuring or strangulating it when rotating the lateral flap (Mericli; Shokrollahi). - Included tissues: skin/subcutaneous/fascia/muscle; thickness profile; arc of rotation; common variants/anomalies. - Typical harvests: muscle-only hemigastrocnemius (medial or lateral head) is the standard; myocutaneous variants are possible but often require skin grafting or wider donor closure (Mericli; Shokrollahi). - Distal tendon: the muscle is commonly detached from the Achilles with retention of a distal tendinous cuff to aid inset — recommended cuff ≈ 1 cm (Mericli; Shokrollahi; Sbitany). - Size/shape: medial head is generally larger and longer (medial head length ≈ 15 cm; lateral ≈ 12 cm reported averages) and therefore preferred for reach and bulk (Mericli). - Arc of rotation: medial head routinely reaches anterior knee, popliteal fossa, and proximal/mid tibia; reach can be increased by freeing origin from femoral condyle and/or by scoring deep/superficial fascia to expand surface area (Mericli; Shokrollahi; Sbitany). - Common variants/limitations: both heads are independent and can be used together for large defects but sacrificing both is not routinely recommended because of functional loss; inferiorly based reverse flap variants have been described but proximal pedicle is dominant and reverse use is not routinely recommended (Shokrollahi). ## Dissection Steps 1. Positioning, markings, landmarks. - Position: most commonly supine with the knee flexed; for medial head harvest place hip abducted and foot “frog‑leg” to expose medial posterior calf. Prone or lateral positions are alternatives depending on defect and surgeon preference (Mericli; Sbitany; Shokrollahi). - Markings: mark the popliteal crease/transverse line where sural branches emerge; mark the longitudinal midline raphe between medial and lateral heads or a posterior paramidline incision line just medial to midline for medial harvest (options per surgeon — see below) (Mericli; Shokrollahi; Sbitany). - Incision length: longitudinal incision commonly 10–15 cm for exposure of the muscle belly and proximal pedicle when needed (Sbitany). 2. Plane (suprafascial/subfascial), perforator identification (handheld/IO Doppler). - Skin/subcutaneous/fascia: incise skin and subcutaneous tissue; divide superficial fascia to expose the superficial posterior compartment. For myocutaneous harvest include fascia and proximal fascia/perimuscle fat to capture musculocutaneous perforators (Mericli; Shokrollahi). - Identify superficial landmarks intraop: plantarflexion against resistance highlights muscle contour and helps assess reach; identify and preserve saphenous vein for medial harvest and lesser saphenous/sural nerve in the midline septum (Sbitany; Mericli; Shokrollahi). - Dissection plane: elevate posterior/superficial fascia off gastrocnemius (largely avascular areolar plane). Then enter the deep plane between gastrocnemius and soleus to free the deep surface (sharp/blunt) — plantaris tendon lies in this plane and should be preserved if present (Sbitany; Shokrollahi). - Perforator identification: routine Doppler for gastrocnemius muscle harvest is not required for muscle-only flaps; when designing a myocutaneous paddle focus on proximal perforators (use Doppler to include proximal musculocutaneous perforators) (Mericli). 3. Pedicle dissection: exposure, control, division; transfer/inset; perfusion checks. - Separation of heads: identify raphe between heads (midline streak of fat or muscle fiber direction) and separate the half to be elevated by sharp/cautery dissection; ligate small inter‑head perforators as encountered (Sbitany; Shokrollahi). - Distal tendon division: transect muscle from Achilles tendon leaving ≈ 1 cm distal cuff of tendon on the flap (Sbitany; Mericli; Shokrollahi). Sbitany specifies transection one fingerbreadth above the confluence forming the Achilles. - Proximal mobilization: elevate muscle distal→proximal until flap can inset without tension. Visualization of the sural vessels is optional; often stop proximal dissection once adequate rotation achieved to minimize pedicle risk. If more reach is needed, dissect to the sural vessels and skeletonize pedicle, or divide muscle origin from femoral condyle (if origin detached, continuously inspect pedicle for tension) (Sbitany; Shokrollahi). - Protect neurovascular structures: identify and protect sural nerve and lesser saphenous vein in midline; avoid injury to common peroneal during lateral head work (Mericli; Shokrollahi). - Transfer and tunneling: pass flap through a relaxed subcutaneous tunnel or open the bridge; ensure tunnel is wide and fascia relaxed — incise fascial underside of the bridge if tight. Externalize flap if congestion suspected (Sbitany; Shokrollahi). - Inset and skin coverage: most commonly place the previous posterior/superficial muscle surface outward as it accepts skin graft reliably; secure muscle circumferentially to wound edges and suture distal tendon cuff as an anchoring point (Sbitany; Mericli). - Perfusion checks: clinical inspection of color, bleeding, turgor and absence of tension/kinking of pedicle; check pedicle region after inset for stretch; no specific implantable monitoring protocols detailed in sources — use frequent clinical checks and address any pedicle kinking immediately (Sbitany; Mericli). 4. Donor-site closure techniques. - Muscle-only harvest: donor site can usually be closed primarily over a closed suction drain (Mericli; Shokrollahi). - Myocutaneous harvest: skin paddle wider than about 6 cm commonly requires skin grafting and may preclude primary closure; layered closure with drainage if a flap with smaller paddle is used (Mericli; Shokrollahi). - Wound care: consider negative-pressure dressings to secure split-thickness grafts to the muscle (Sbitany; Shokrollahi). ## Indications and Contraindications - Indications: common reconstructive scenarios; size limits; need for thin vs bulky; sensate needs. - Primary indications: soft-tissue defects around the knee, popliteal fossa, and proximal (superior) third of the tibia — commonly for trauma, post‑arthroplasty wound breakdown with exposed hardware, oncologic resections, infections, necrotizing fasciitis, and contracture releases (Sbitany; Mericli; Shokrollahi). - Typical defect coverage: medial hemigastrocnemius reliably covers anterior knee, the inferior half of the knee joint, popliteal fossa, and proximal tibia. Larger/ high knee defects may need alternative or combined flaps — both heads can be used for larger defects but this sacrifices more calf function (Shokrollahi; Mericli). - Bulk: muscle-only flap provides well‑vascularized bulk for dead space and hardware coverage and is later skin‑grafted; myocutaneous variant is bulkier and donor site morbidity often limits its use (Mericli). - Sensate reconstruction: motor branches are typically divided; flap is not commonly used as sensate flap. - Contraindications: vascular disease, prior surgery/radiation (relative/absolute), comorbidity risks. - Relative/absolute: significant disease of popliteal or sural vessels (documented PVD) is a relative contraindication — preoperative CTA/angiography recommended if PVD suspected (Sbitany; Mericli). - Prior surgery, trauma, or radiation that has disrupted the popliteal/sural axis or local soft tissue may preclude reliable pedicle; prior damage to the sural nerve/lesser saphenous territory increases risk (Sbitany; Shokrollahi). - Lateral head harvest: avoid when risk to common peroneal nerve is unacceptable (Mericli). ## Postoperative Care - Monitoring schedule/method (clinical, Doppler, implantable probe), warming, antithrombotic practice, positioning/splinting, drains, mobilization, diet/analgesia. - Immediate monitoring: frequent clinical checks (color, turgor, capillary bleeding through graft or muscle) — no specific Doppler protocol described for pedicled gastrocnemius in the cited texts; assess pedicle region for stretch/kinking after inset (Sbitany; Mericli). - Immobilization/positioning: place limb in a knee immobilizer to reduce muscle stretch and edema. Immobilization typically maintained for about 2 weeks; early knee flexion and ambulation start at ~2 weeks if healing allows (Sbitany). - Weight-bearing: non‑weight bearing or limited weight bearing as indicated by overall reconstruction and orthopedic requirements; use crutches/walker per surgeon (Sbitany). - Dressings and graft care: skin graft over muscle protected for 5–7 days with either negative‑pressure therapy or bolster dressing (Sbitany). - Drains: closed suction drains at donor site recommended; remove per standard output criteria (Mericli; Shokrollahi). - Antithrombotic/medical optimization: standard VTE prophylaxis per institutional protocols; if venous insufficiency or DVT history, consider preop venous imaging as indicated (Sbitany). - Return-to-OR thresholds and time windows. - Immediate return to OR: any expanding hematoma, loss of flap bulk/rapid ischemia signs, severe venous congestion that does not resolve after bedside measures (limb adjustment, relieving tunnel) — evacuate hematoma immediately to prevent pedicle compression (Sbitany; Shokrollahi). - Early return: infection with purulence or early flap compromise — re‑elevation, washout, and irrigation indicated promptly (Sbitany). - Delayed reconstruction: complete flap loss often mandates a secondary free flap reconstructive plan (Sbitany). ## Complications (rates & management) - Venous congestion, arterial thrombosis, partial/total loss, infection, fat necrosis; include percent/frequency if present. - Reported numeric complication rates are not provided in the cited chapters. Listed complications and management are: - Hematoma: may compress pedicle and cause venous outflow obstruction → immediate evacuation in the OR; control bleeding and reassess flap perfusion (Sbitany; Shokrollahi). - Venous congestion: if present, check for tunnel tightness or pedicle kinking; release/ open tunnel or externalize muscle; re-explore if congestion persists (Sbitany). - Arterial insufficiency/thrombosis: rare for pedicled gastrocnemius; if suspected, urgent re‑exploration and pedicle assessment required. - Infection: prevent with adequate debridement prior to flap; treat established infection with re‑elevation, aggressive washout, debridement, and targeted antibiotics (Sbitany). - Partial/total flap loss: if total loss occurs, options include planning a free flap for reconstruction; partial loss may require debridement and secondary closure or grafting (Sbitany). - Donor-site problems: seroma/hematoma — manage with evacuation/drainage; contour deformity and weakness are possible but harvesting one head generally spares adequate plantarflexion in most patients (Shokrollahi; Mericli). - Functional deficit: sacrificing a single head seldom causes significant gait impairment; simultaneous sacrifice of both heads is generally avoided (Shokrollahi). - Management algorithms (re-exploration, leeching, thrombolysis): what, when, how. - Hematoma/active bleeding → immediate return to OR for evacuation and hemostasis (immediate). - Venous congestion due to external compression/tight tunnel → bedside release/opening of tunnel; if unresolved, return to OR for exploration (urgent). - Infection → re-elevation and aggressive washout with debridement; culture-directed antibiotics (urgent). - Arterial thrombosis/acute ischemia → urgent re‑exploration; restore inflow if possible (urgent). - Complete flap loss → plan secondary reconstruction (timing depends on infection/soft tissue bed; often after debridement and bed optimization) (Sbitany). ## Key Clinical Pearls - Retain a distal tendinous cuff of ≈ 1 cm on the flap when dividing from the Achilles — useful for secure inset and offsets tension from muscle fibers (Mericli; Shokrollahi; Sbitany). - Medial head is the workhorse: larger, longer (medial ≈ 15 cm vs lateral ≈ 12 cm), greater arc of rotation, and avoids common peroneal nerve risk — preferentially use medial head when possible (Mericli). - Stop proximal dissection once the flap reaches the defect without tension; routine skeletonization to the sural pedicle is unnecessary and increases risk — only dissect to pedicle when increased reach is required (Sbitany; Shokrollahi). - If tunneling, ensure the skin/fascial bridge is lax — incise underlying fascia or convert to open transfer if any compression or congestion is suspected (Sbitany). - For myocutaneous designs, keep skin paddle width ≤ ~6 cm if you want primary donor closure; otherwise expect to graft donor site (Mericli). - Scoring the deep and superficial fascia over the muscle increases surface area and can improve the ability to cover wider defects and graft take (Mericli). - Preoperative vascular imaging (CTA/angiography) is reserved for patients with suspected peripheral vascular disease, prior popliteal injury, or when pedicle patency is in question (Sbitany). - Hematoma is a surgical emergency for pedicled gastrocnemius flaps — evacuate immediately to avoid pedicle compression and flap loss (Sbitany; Shokrollahi).