Flap reconstruction of the lower extremity

INTRODUCTION — Following initial limb management to manage any fractures, bone loss, or neurovascular injuries, a combination of reconstructive techniques may be required to provide optimal closure of lower extremity wounds, and surgeries may need to be staged. Lower extremity dysfunction and loss of the form may be due to a variety of etiologies, including trauma, nonhealing wounds, infection, malignancy, degenerative disease, or congenital deformities.

The principles of flap reconstruction of the lower extremities are reviewed. The discussion focuses largely on the management of the severely traumatized lower extremity; however, the basic concepts that guide reconstruction are similar regardless of the antecedent etiology.

Soft tissue reconstruction of pressure-induced skin and soft tissue injuries involving the lower extremity is reviewed separately. (See "Surgical management of pressure-induced skin and soft tissue injuries", section on 'Surgical wound closure'.)

Soft tissue reconstruction of the upper extremity is also reviewed separately. (See "Severe upper extremity injury in the adult patient" and "Surgical reconstruction of the upper extremity".)

ETIOLOGIES OF SOFT TISSUE LOSS — Multiple etiologies may lead to soft tissue loss requiring flap reconstruction to provide soft tissue coverage and wound closure. Initial limb management involves fixation of fractures, restoration of bony loss, and repair of neurovascular injuries, as indicated. A combination of reconstructive techniques may be required to provide optimal closure of a particular wound, and surgeries may need to be staged.

Initial evaluation and management prior to surgical flap reconstruction are reviewed elsewhere and in separate topic reviews for each etiology. (See "Surgical management of severe lower extremity injury".)

●Traumatic injury (See "Severe lower extremity injury in the adult patient" and "Surgical management of severe lower extremity injury".)

●Nonhealing wounds (See "Management of chronic limb-threatening ischemia" and "Management of diabetic foot ulcers".)

●Infection/osteomyelitis (See "Necrotizing soft tissue infections" and "Surgical management of necrotizing soft tissue infections" and "Nonvertebral osteomyelitis in adults: Treatment".)

●Degenerative disease (See "Total hip arthroplasty" and "Total knee arthroplasty" and "Complications of total hip arthroplasty" and "Complications of total knee arthroplasty".)

●Osteonecrosis (See "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)" and "Treatment of nontraumatic hip osteonecrosis (avascular necrosis of the femoral head) in adults".)

●Malignant tumors (see "Surgical resection of primary soft tissue sarcoma of the extremities" and 'Fillet of sole flap' below)

●Congenital disease – The goal of reconstruction of congenital disease affecting the lower extremity is to preserve future growth and reduce the risk of limb-length discrepancies. Severe limb defects can be treated with lengthening operations. Amputation with prosthetic reconstruction is also an option; however, prostheses are associated with potential infection and exposure and are without future growth potential.

SOFT TISSUE FLAP RECONSTRUCTION — Flaps used for soft tissue reconstruction are categorized based on the tissue they contain, such as cutaneous, fascial, muscle flaps, or combinations of these, such as fasciocutaneous and myocutaneous flaps [1]. (See "Overview of flaps for soft tissue reconstruction", section on 'Flap nomenclature'.)

For lower extremity soft tissue reconstruction, debate continues whether muscle flaps or fasciocutaneous flaps are more desirable, but there are some advantages to each [2,3] Data suggests that muscle flaps may have lower complication rates in patients undergoing free tissue transfer in the setting of peripheral vascular disease [4]. Patients report similar improvements in function regardless of flap type [5]. Osteocutaneous flaps for closing bony gaps are discussed above. (See "Surgical reconstruction of the lower extremity", section on 'Osteocutaneous free flaps'.)

When planning soft tissue reconstruction of lower extremity wounds, the reconstructive surgeon uses the principle of the "reconstructive ladder," which is commonly referenced in the plastic surgery literature [6]. Closure options are evaluated starting with the simplest (ie, healing by secondary intention) and moving up the ladder to the most complex (ie, free tissue transfer). By starting with the simplest option that maximizes function of the lower extremity, the reconstructive surgeon has a "salvage" option in the event of failure. (See "Overview of flaps for soft tissue reconstruction", section on 'Principles of reconstruction'.)

A clear view of the vascular anatomy of the lower extremity and potential donor sites is also critical for reconstructive planning. The patient should undergo a careful pulse exam, and any abnormalities should prompt computerized tomography angiography or catheter-based arteriography in patients with peripheral artery disease or any prior vascular interventions. High-resolution ultrasound can also evaluate vascular characteristics at the recipient and donor sites. Familiarity with ultrasound-based flap design is particularly important for perforator flap reconstruction and when using flaps with less reliable vascular anatomy because it results in reduced intra-operative complexity and faster operative times [7].

A combination of reconstructive techniques may be required to provide optimal closure of a particular wound. As an example, a Gustilo Grade IIIB injury may have an open tibia that needs bulky soft tissue coverage, but another subunit of the wound (perhaps more laterally located over calf muscles), may have suffered primarily from a degloving injury that can be skin grafted. (See "Skin autografting".)

Locoregional flaps — Many locoregional flaps including advancement, rotation, and transposition flaps are available for soft tissue coverage in the lower extremity. Local cutaneous flaps can be based on random or axial (named) vascular patterns. Random pattern flaps are limited by their size, arc of rotation, and width-to-length ratio design [8]. The V-Y flap is a random pattern flap that provides excellent contour, sensate coverage, and minimal morbidity for lower extremity reconstruction [9,10]. Bi-pedicled and keystone perforator flaps are gaining in popularity as local flap options for lower extremity wounds [11-13].

A flap can be rotated on a single perforator complex up to 180 degrees for defect coverage (ie, propeller flap) [14]. The propeller flap is commonly based on peroneal and posterior tibial artery perforators and is an option for the majority of coverage of the lower limb, below the knee, as distal as the lateral malleolus, Achilles tendon, and dorsum of the foot [15,16]. However, if other more reliable flaps are available, propeller flaps are not typically a first choice, given the high rate of partial flap loss [17]. Maximal rotation of the flap requires a full island dissection of the flap; proximal dissection of the perforator may help prevent kinking and resultant venous congestion.

Muscle flaps have traditionally been used for exposed hardware and osteomyelitis. They are also first-line flaps for wound beds when future radiotherapy is planned in order to avoid nonunion, fracture, or exposed hardware [18,19]. Muscle flaps such as the latissimus dorsi flap have a large surface area and are well vascularized. The use of perforator flaps (eg, medial sural artery perforator) has increased, and these provide a longer pedicle length due to an intramuscular dissection, decreased donor-site morbidity, and optimal aesthetic results [20]. Cutaneous flaps such as the radial forearm and scapular flap provide pliability and good aesthetic results.

Fasciocutaneous flaps such as the lateral arm flap, medial sural artery perforator (MSAP), and anterolateral thigh (ALT) are good choices for wounds of the plantar weight-bearing surface of the foot and around the metaphyseal regions of the ankle and knee, such as is in the setting of exposed hardware [21,22]. In the case of secondary procedures, these flaps are more easily re-elevated.

Neurotization, or performing a nerve coaptation during free tissue transfer, has gained popularity, particularly for reconstruction of soft tissue defects and complex injuries of the foot/heel. This may aid reconstructive efforts in patients with neuropathic conditions such as spinal cord injuries or diabetes. While neurotized and non-neurotized flaps perform the same in the long term, neurotization results in quicker return of sensibility [23]. By extension, cited benefits of neurotization include improved sensibility (light touch, pain, two-point discrimination) and quicker return to activities of daily living and ambulation [24].

Fillet of sole flap — For patients in whom limb salvage is not an option, the unique and durable composition of the plantar skin of the foot can be used to the patient's advantage in stump reconstruction. The skin can be raised as a pedicled flap, usually based on the posterior tibial artery and venae comitantes, or as a free flap. To avoid pedicle kinking as the residual limb is shortened, the authors prefer the latter option. The thick skin is ideal for weight-bearing on a prosthesis, and the septae between the skin and plantar fascia helps skin resist breakdown from shear. The flap can be transferred as sensate tissue. Since preserving bony length in amputations is a surgical priority (the more proximal the amputation, the greater the functional impairment and the fewer the prosthetic options), the fillet of sole flap can be a powerful tool in obtaining soft tissue coverage over remaining bone. The flap also has the potential to grow in children [25-27].

RECONSTRUCTION BY LOCATION — The general location of the lower extremity wound will affect the type of reconstruction that is used.

Thigh defects — There are a variety of flap options when reconstructing thigh defects, and the majority of defects can be reconstructed by locoregional means [28]. Local tissue rearrangements such as rotational, keystone, or V-Y flaps are simple options when possible [21].

A review of reconstruction following soft tissue sarcoma resection demonstrated that pedicled thigh muscle (rectus femoris and vastus lateralis) and rectus abdominis flaps were most commonly used for the proximal third of the thigh, pedicled thigh muscle flaps for the middle third, and pedicled gastrocnemius for the lower third [28]. Predictors of the need for free flap reconstruction included location in the middle third of the thigh and larger/wider defects (13.6 cm for free flaps versus 8.9 cm for all other types of reconstruction) [28]. Free flaps can also be neurotized to restore function. Examples of this include the reconstruction of an anterior thigh defect with innervated latissimus dorsi flap and restoration of knee extension [29], or with contralateral anterolateral thigh (ALT) with tensor fascia lata and motorized vastus lateralis [30,31].

Gluteus maximus can be used as a locoregional flap to cover defects over the perineum, trochanter/hip, and upper thigh and in cases of recalcitrant periprosthetic joint infections or recurrent instability related to total hip arthroplasty [32,33]. The gluteus maximus flap can be based on one of the gluteal arteries with the muscle-split preserving function or based on the lateral femoral circumflex artery to allow posterior thigh coverage [32]. Every attempt is made to avoid significant muscle sacrifice, particularly in ambulatory patients, to preserve maximal limb function.

The ALT flap has evolved as an ideal soft tissue workhorse flap for lower extremity reconstruction [34] (see "Overview of flaps for soft tissue reconstruction", section on 'Anterolateral thigh flap'). The descending branch of the lateral femoral circumflex artery and its venae comitantes serve as the dominant pedicle of the flap and traverse in an oblique fashion in the groove between the rectus femoris and vastus lateralis. It is innervated by the lateral femoral cutaneous nerve of the thigh. Depending on the location of the defect to be reconstructed, a pedicled reverse-flow or free ALT are commonly used and versatile flap options [16]. The ALT flap is outlined along the axis of anterior superior iliac spine (ASIS) to the superolateral corner of patella, and septocutaneous or musculocutaneous perforators can be identified prior to incision with the aid of a Doppler. Perforators are more commonly musculocutaneous (>80 percent) compared with septocutaneous (<20 percent). An 8 by 25 cm skin paddle can be raised, and primary closure is still possible in many cases. Various amounts of vastus lateralis muscle around the cutaneous perforator and the descending branch can be included in the harvest when muscle is needed. A proximally based pedicled ALT can be used to cover defects of the ischial tuberosity and greater trochanter. A distally based design, which is supplied by the lateral superior genicular artery, may reach as far the lateral knee and proximal tibia for coverage [35]. It may be necessary to delay the distally based ALT to minimize risk of partial flap loss. A drain is used at the donor site location in the intramuscular dead space.

Other flaps based on the lateral femoral circumflex system include the vastus lateralis, tensor fascia lata (TFL), and rectus femoris flaps. The vastus lateralis is commonly used for salvage of hip wounds and closure of trochanteric pressure sores. TFL has a constant/reliable perforator anatomy and is a good backup when ALT is not an option [36,37]. As a pedicled flap, it can reach the groin and ischium and can even incorporate skin and/or iliac bone for osteomusculocutaneous coverage of defects in the proximal lower limb. However, TFL is not typically a first choice, as it has a thin/small muscle belly and long fascial extension [38]. The rectus femoris may reduce knee extension up to 20 percent and therefore has been criticized for significant donor site morbidity [39,40]. Performing a vastus medialis to lateralis muscle stenography can be used to reduce or eliminate distal knee extension weakness.

The antero-medial thigh flap or medial thigh flap can be used to cover wounds in the groin and can be fashioned up to 10 x 20 cm in size. The posteromedial thigh flap is based on the deep femoral or medial circumflex femoral artery and can be elevated as high as the gluteal crease to cover defects from the groin to the popliteal fossa [41]. Primary closure of the donor site is usually possible if the width is less than 10 cm. The gracilis flap is based on the terminal branch of the medial circumflex femoral artery and can be used for perineal and ischial coverage as a muscle only or myocutaneous flap. Although this flap lacks bulk, it has a straightforward dissection with minimal donor site morbidity.

Knee defects — In the setting of exposed knee joint or hardware, coverage with more substantial well-vascularized tissue is essential. The gastrocnemius offers separate muscle or musculocutaneous flaps to be raised on pedicles along the lateral or medial sural arteries. The median raphe is split to allow for medial or lateral gastrocnemius harvest and rotation, and the distal tendinous portion is divided.

The gastrocnemius flap is the workhorse flap for popliteal/knee region coverage but also for distal femur and proximal tibia (see "Overview of flaps for soft tissue reconstruction", section on 'Medial gastrocnemius flap'). The medial muscle offers greater surface area (ranges from 5 to 9 cm in width and from 13 to 20 cm in length) for coverage and a larger arc of rotation. The lateral muscle is limited by the fibular head and comes with the potential risk of common peroneal nerve injury. The gastrocnemius flap can only be used in scenarios in which soleus is intact, as rehabilitation and walking are dependent on ankle plantar flexion. The medial gastrocnemius flap is elevated through a medial incision adjacent the tibia. This incision can be entirely separate from the recipient site, or, often, it connects to the recipient site at its most inferior aspect. The muscle is elevated from distal to proximal starting at the junction of the middle and distal third of the calf, taking care not to injure the Achilles tendon. The insertion site of the Achilles is transected, and the flap is lifted out of its bed. Dissection then proceeds proximally, releasing the muscle from all surrounding fascial attachments. The vascular pedicle enters the muscle high in the calf, just posterior to the knee joint, and is usually not formally dissected during flap elevation. The arc of rotation of this flap will cover the distal thigh down to the middle third of the calf. The transposition of the flap can be limited by the muscle fascia. Scoring the muscular fascia transversely on the deep surface and/or releasing the origin on the femur allows for greater reach [42]. Following inset of the muscle flap into the defect, a split-thickness skin graft can be applied, and a negative pressure wound dressing or bolster dressing is used to hold the skin graft in place. The knee is immobilized temporarily while the flap and overlying graft heal.

There are several reliable perforator flaps in the knee region. Perforator flaps have many desirable traits for knee soft tissue coverage [43-45]. Peripheral neovascularization is predictable, and re-elevation can be easily and safely performed for purposes of secondary procedures [46]. Proximal or distal-based peninsular flaps based on perforators of genicular branches, similarly small island advancement flaps, or keystone flaps may be possible for smaller defects [47,48]. Flaps based on the saphenous artery and surrounding perforators of the medial thigh and vastus medialis can be used for reconstruction of moderate-sized defects around the knee [49-51].

The lateral genicular artery flap can also be used to reconstruct defects of the knee and lower thigh [52]. It is favored for this purpose due to its fast and easy harvest and good aesthetic results [52,53]. The skin island is designed on the lateral aspect of the lower thigh and is based on the perforating branch of the superior genicular artery. The flap is raised as an island, and the donor site is closed primarily. The medial sural artery perforator (MSAP) flap can be harvested on the same source pedicle as the gastrocnemius without including the muscle itself [54]. A consequence of the shared blood supply with the gastrocnemius flap is that the MSAP flap is not an option in patients who have had a failed prior gastrocnemius flap. The pedicle can be up to 9 to 16 cm in length depending on the location of the chosen perforator and flap design about that perforator [55]. MSAP perforators are considered somewhat more fragile compared with those of the ALT flap, requiring more delicate dissection [56]. There is also considerable anatomical variability of the location of medial sural artery perforators, adding complexity to the anatomic dissection [57]. Prophylactic soft tissue coverage with the local MSAP or ALT free flap in high-risk patients prior to definitive knee arthroplasty essentially eliminates future related complications and infection risk.

For larger defects, another option could be a distally based ALT flap. The reverse-flow ALT is a popular choice given its large skin flap size, long pedicle, and the ability to couple TFL with the flap for extensor mechanism reconstruction [35,58,59]. The reverse-flow ALT is based on a communication of either the deep femoral artery or lateral superior genicular artery with the lateral circumflex femoral artery. Again, we caution that prior orthopedic interventions or trauma may have injured the distal collateral circulation [60]. Note that if the skin perforator arises from an oblique branch and not the descending branch of the lateral circumflex femoral, or if the perforator has a more distal location, this alternative may not even safely reach the knee region [61]. In addition, there is the risk of venous congestion high as 50 percent with the reverse-flow ALT [62], but this can be lessened by supercharging with saphenous vein outflow [16].

Proximal leg defects — The proximal and middle third of the leg are generally amenable to local flaps. The gastrocnemius and soleus are the traditional workhorse flaps for the proximal and middle third of the leg, respectively. In general, these local muscle flaps will not cover defects larger than 30 cm² [42].

The gastrocnemius and hemi-soleus pedicled flaps have traditionally been used for upper and middle one-third defects of the lower extremity. The gastrocnemius is used for proximal tibia, knee, and patellar tendon coverage and can be mobilized to allow suprapatellar distal femur coverage. The soleus can be used for defects of the middle third of the lower leg and can be split to form a hemisoleus flap given its dual pedicle supply and bipennate morphology [63]. The use of the soleus has been criticized for risk of ankle flexion weakness and loss of venous return.

Advances in surgical technique have allowed for the use of perforator-based local flaps such as reverse flow and propeller flaps [64,65]. For smaller defects in this region, the propeller flap provides good aesthetic and functional results. However, larger donor site defects require the use of skin graft for coverage [66]. The previously discussed MSAP flap can be used to cover defects of the anterior and posterior upper third of the leg. If harvested with a width less than 4 to 5 cm, primary closure is possible.

Distal leg defects — Traditional teaching holds that defects in the distal third of the tibia and onto the foot require free flap coverage. Free flaps such as the latissimus dorsi flap provide greater bulk for filling large wounds, can be harvested with long pedicles, and in general have larger diameter vessels, easing the technical aspect of micro anastomoses. Free muscle flaps provide excellent coverage for debrided bone and soft tissue, as well as improve the vascularity and leukocyte function of the wound [67,68].

Adipofascial or fasciocutaneous pedicled flaps can be based proximally or distally on perforating vessels of the posterior tibial and peroneal arteries. The dissection is relatively straightforward and provides adequate coverage for small- to medium-sized defects of the distal lower extremity, including the Achilles tendon [69].

Pedicled perforator flap coverage of small to medium defect sizes (<70 cm²) is a cost-effective option in distal leg reconstruction [70]. The posterior tibial artery perforator flap (PTAP) and pedicled peroneal artery perforator (PAP) are valuable reconstructive flaps in this region [71,72]. The pedicled PAP flap can be designed as a propeller, peninsular, advancement, proximally or distally based island flap, and can cover defects in the pretibial area [72]. PAP flaps have been reported to have a higher rate of venous congestion than other flaps [16,71]. PTAP flap is commonly raised as a propeller, peninsular, or distally based island flap and has the advantage of being both thin and pliable. With a skin paddle up to 6 x 18 cm, it can cover anterior shin, medial malleolar, and Achilles territories [73-75]. Other pedicled perforator flaps such as the lateral sural artery perforator flap, lateral superior genicular artery flap, and anterior tibial artery perforator flap are less commonly used. Skin grafting of the donor site is necessary for most of the above mentioned pedicled perforator flaps.

Despite the above pedicled options, the paucity of soft tissue of the distal third of the extremity and zone of injury frequently necessitates free tissue transfer. Common muscle or myocutaneous free flap options include the gracilis, latissimus, and rectus abdominis. ALT is the workhorse perforator free flap for this region, but the PMT and AMT are also good options [76]. Other perforator flaps that can be used for lower extremity transfer include the lateral arm, thoracodorsal artery perforator, and the superficial circumflex artery perforator flaps.

For tendon reconstruction, the deep fascia of the ALT and TFL can also be used as a substitute [77]. The Achilles tendon itself can be reconstructed with autograft, such as vascularized fascia lata or gracilis myotendinous unit, or allograft [77-79].

Foot and ankle defects — The foot and ankle area merits special consideration when discussing soft tissue coverage [80,81]. The dorsal surface is critical for proper shoe fitting and is characterized by paucity of soft tissues and highly visible contours. The plantar surface is glabrous and must withstand sheer forces and direct weight-bearing. It is important to match the flap to its future function; bulky flaps should be avoided for the reconstruction of dorsal foot and ankle subunits, and thin or excessively mobile flaps should not be used for reconstructing weight-bearing units [81].

Local flaps of the foot are used for rear or midfoot defects but are limited by their arc of rotation and small size. Local muscle flaps include the abductor hallucis, abductor digiti minimi, and flexor digitorum brevis flaps to cover small heel defects.

●The flexor digitorum brevis is accessed through a midplantar incision extending back to the calcaneus and should be elevated with the plantar fascia. This muscle is small but can be used following tarsal tunnel release/neurolysis or to resurface the heel in instances of calcaneal infections.

●The extensor digitorum brevis can be used to cover the lateral malleolus. It originates from the talus and the dorsolateral surface of the calcaneus and is based on the lateral tarsal artery [82,83].

●A neurovascular island flap can be elevated from the lateral side of the great toe for coverage of plantar and metatarsal head ulcers. A V-Y advancement flap based on medial plantar artery perforators may also be used in diabetic patients for coverage of metatarsal head ulcers.

Lower extremity reconstructive surgeons should be familiar with the medial plantar artery or "instep" flap. When used as a rotation flap, it has the advantage of providing sensate (via branches of medial plantar nerve), similar thickness plantar-based skin for resurfacing of small defects up to 6 x 12 cm on the heel. It can also be used on the medial aspect of the first and second metatarsal area as a V-Y advancement [21,84-86]. The pedicle of the flap lies between the flexor digitorum brevis and abductor hallucis. The abductor hallucis will need to be divided to facilitate enough arc of rotation. When extending the incision proximally into the tarsal tunnel, it is important to preserve medial calcaneal nerves to avoid potential numbness and neuroma formation. A split thickness skin graft can be used for the donor site with application of a bolster dressing and offloading, typically for a period of three weeks. Given the donor site morbidity, alternatives to this flap should be considered in diabetic patients with Charcot foot.

Other local flaps for heel coverage include the peroneal artery flap, reverse sural flap, dorsalis pedis flap, supramalleolar flap, anterior tibial fasciocutaneous flap, and abductor myocutaneous flap. The lateral supramalleolar flap, a fascial turnover flap, is distally based upon the perforating branch of the peroneal artery 5 cm above the lateral malleolus. It can provide up to 8 x 6 cm of dorsal foot and ankle coverage [87,88]. The lateral calcaneal artery perforator flap can be used to reconstruct small defects of the hindfoot and lateral ankle, with minimal donor site morbidity [89,90]. The sural flap, when distally based on a reverse flow through the peroneal artery and the communicating vascular medial sural network, can cover defects of the ankle and heel [91,92]. Important landmarks are the small saphenous vein and sural nerve, which should bisect the cutaneous paddle. A wide fascial cuff can be fashioned to help avoid congestion. The dorsalis pedis pedicled fasciocutaneous flap can also be used to cover defects of the anterior, lateral, or medial ankle.

Wounds of the dorsal surface around the ankle with exposed underlying bone and tendons are most often treated with free tissue transfer [93]. Common recipient vessels in this area include the anterior tibial artery, posterior tibial artery, and the great and small saphenous veins. Many orthoplastic surgeons prefer the use of free muscle flaps with overlying split-thickness skin grafts, such as the gracilis, latissimus dorsi, and rectus abdominis flaps. Others support the use of fasciocutaneous flaps, such as parascapular, radial forearm, and ALT. Anecdotally, there is no difference with respect to re-ulceration rate or gait pattern when comparing muscle or fasciocutaneous flaps. Muscle flaps and skin grafts are an adequate way to reconstruct the heel, allowing significant weight bearing without breakdown [94]. Data also suggest no relationship between sensibility and stability for neurotized fasciocutaneous flaps beyond one year [95,96].

The bones of the lower extremity that most commonly require reconstruction either due to avascular necrosis or nonunion are the femoral head (reviewed below) talus and navicular. The iliac bone crest and medial femoral condyle (MFC) flaps can be used if the defect is less than 3 to 4 cm, and the fibula can be used for larger-sized defects [97,98]. The MFC is commonly employed in patients with complex hindfoot pathology that requires additional vascularized bone to optimize the potential for osseous healing and successful orthopedic treatment. Osseous union can be achieved in greater than 90 percent of these patients; risk factors for nonunion include obesity body mass index (BMI) >35 and history of prior failed arthrodesis [98].

One additional option for metatarsal bony reconstruction is the osteocutaneous radial forearm flap. This flap provides a thin fasciocutaneous skin paddle ideal for the dorsal foot, long reliable vascular pedicle, and can be harvested with a length of the distal radius approximately 8 to 10 cm in length and 1 to 1.5 cm in width [99-101]. Of course, there is a risk of fracture of the radius when performing osteotomies for bone harvest, and special care must be taken to avoid this complication.

POSTOPERATIVE CARE — The reconstructive surgeon should remain vigilant in the postoperative period to ensure the ongoing healing of the repair [102].

Flap monitoring and wound care — Flap temperature, color, and texture should be recorded hourly by the nursing staff. Nursing staff who regularly care for flap reconstructions who are educated in basic flap anatomy and physiology are best equipped to identify the first signs of something awry. For the most part, clinical exam remains the gold standard following flap reconstruction. This includes assessing for capillary refill, skin color, and tone.

Monitoring the inflow to a free flap is prudent while the patient is in the hospital and may allow for earlier detection and salvage in the event of flap circulation compromise [103,104]. Some high-volume microvascular centers have early monitoring protocols in which flaps are checked at frequent intervals in the early postoperative period by the involved surgeons to better detect early compromise. Identifying a perforating vessel that can be easily auscultated with an external hand-held Doppler is the most routine method of surveillance. Other methods of monitoring, such as transcutaneous oxygen monitoring (eg, Vioptix) and implantable devices (eg, Cook-Swartz Doppler) should not replace clinical exam, as false-positive alarms may result in needless take-backs [105]. Care should be taken in using the Cook probe on small vessels in that the silastic cuff can shift and obstruct flow. If a venous Cook probe is also used, it may take 10 to 12 hours for the venous signal to be audible.

Prophylactic systemic anticoagulation is mandatory to reduce the risk for venous thromboembolism. To our knowledge, no prospective studies have evaluated the potential benefit or harm for flap survival for anticoagulation (prophylactic or therapeutic). In fact, one study found that only subcutaneous heparin, given at doses for venous thromboembolism (VTE) prevention, showed a statistically significant effect on free tissue transfer survival compared with antithrombotic agents like heparin, dextran, and aspirin [106].

For microvascular reconstruction to the lower extremity, we initiate aspirin 325 mg daily, if not already taking, and continue postoperatively for two weeks during the period that new vascular intima is forming across the anastomotic site. The authors do not use dextran, to avoid the potential for volume overload and heart failure. Dextran also has a rare, but potentially catastrophic risk of anaphylaxis.

If prolonged immobility is a concern postoperatively, the patient may be placed on low molecular weight heparin (LMWH) for 30 days or until ambulation/rehabilitation begins. Prophylactic anticoagulation is for prevention of VTE rather than for flap-related reasons. An oral anticoagulant (eg, apixaban) can be used in place of LMWH in patients with renal insufficiency, or for patients who cannot administer or do not wish to have subcutaneous injections. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients".)

Postoperative antibiotics should be dictated by the nature of the patient's original injury (eg, wound contamination, infection) and antibiotic sensitivities at the surgeon's institution. Early infectious disease consult should be obtained in complicated cases. The patient's nutritional status should be maximized.

There may be long periods of non-weight-bearing status and leg elevation to allow for fracture and soft-tissue healing, and patient expectations should be set early. An external fixator can be applied to a foot and ankle reconstruction to act as a kickstand to offload pressure, particularly around the Achilles and posterior heel region. Timing of progression to a dependent position of the lower extremity free flap remains an area of significant debate. Due to severed autonomic nerves at the time of flap harvest, free flaps lack internal flow regulation and cannot signal upstream to limit inflow or maximize venous egress through the normal venoarterial response. As a result, flap swelling can occur if dangled too early, with additional related sequelae including potential venous compromise. However, there is a balance to be struck, as some element of venous pooling and permissive ischemia stimulates neovascularization between the flap and surrounding tissue.

It is our practice to wait approximately two weeks before beginning a dangling protocol.

The other component of monitoring patients who have undergone skeletal reconstruction typically includes serial conventional radiographs or computed tomography/magnetic resonance cross-sectional imaging to assess for osseous healing. Plain films are used for follow-up, and cross-sectional imaging is typically reserved for surveillance of these patients who underwent reconstruction after resection of malignancy, or for those patients experiencing an associated complication of their skeletal reconstruction. Bone scans may also have a role for assessing viability of the skeletal construct.

Postoperative rehabilitation — Most patients are immobilized on bed rest after their lower extremity reconstruction, and elevation of the leg is beneficial in preventing dependent fluid accumulation in the soft tissues of the leg. All areas of potential pressure necrosis (eg, back of heel, calf) should be off-loaded.

An interdisciplinary approach for the leg, foot, and ankle is critical, as issues with weight-bearing may be due to bony, ligament, or muscle abnormalities rather than flap choice. Flap debulking should not be regarded as a complication, as it is often necessary to optimize function and form for shoe fitting. Orthotics may be necessary to improve gait, and shoe inserts may help distribute weight. Reconstruction is only part of the treatment algorithm, and it should be followed by meticulous foot care and long-term vigilance. Plantar flaps are prone to breakdown, and therefore we have a strict non-weight-bearing protocol for the first six weeks following reconstruction, and close follow-up cannot be stressed enough.

Patients' weight-bearing status will be, in part, dictated by the healing status of fracture or osseous union, but also by the stability of the soft tissue repair. Although we advocate early ambulation (especially in older adults to prevent deconditioning and joint stiffness), the surgeon should ensure that early movement does not put their reconstruction at risk. Negative pressure wound therapy (NPWT) is an excellent dressing for skin grafts to the leg, and the continuous suction has been shown to help with skin graft take [107,108]. Though the suction power of a NPWT dressing can permit the patient to ambulate minimally (to a bedside commode a few times a day, for example), the danger of graft shear still exists with this dressing, and the patient should be placed on near bedrest for five days.

In our experience, even the youngest and previously most active patients require aggressive rehabilitation after a major traumatic injury to the lower extremity. Data from the Lower Extremity Assessment Project suggest that maximizing the psychosocial function of the patient contributes to better outcome. Poorer outcomes in lower extremity reconstruction were associated with a low level of education, poverty, lack of private health insurance, smoking, and involvement with disability-compensation litigation [109]. Earlier research about post-injury function also showed that outcome is affected by patients' perceptions of self-efficacy and social support [110].

COMPLICATIONS — Complications after lower extremity flap reconstruction include wound dehiscence, wound infection, flap necrosis, and sensory disorders.

Dehiscence can occur and may be caused by infection, tension, or both. Dehisced wounds in the post-reconstruction period should not initially be closed primarily. Treatment can include negative pressure wound therapy to reduce the size of the defect and other local dressing care with close serial follow-up by the surgeon. Depending on the final size of the defect, the area may be allowed to heal by secondary intention or skin grafts.

Infection can damage or destroy tissue in a reconstructed limb when metabolic demand outstrips the tissues' blood supply. The reconstructive surgeon should have a clear understanding of the orthopedic surgeon's goals for bony fixation in an infected limb, including duration of fixation and plans for weight-bearing status.

Similarly, partial flap necrosis should also initially be managed conservatively, allowing the ischemic area of reconstructed soft tissue to fully demarcate, if orthopedic hardware or bone is not exposed. Areas of incomplete skin graft take should prompt the surgeon to reassess the vascularity of the wound bed and perform any necessary debridement before reattempting placement of a skin graft.

Hardware exposure, infection of the soft tissues, and/or osteomyelitis should be initially managed in similar ways. Tissue cultures should be obtained, and the infectious disease service should be involved early for specific antibiotic recommendations and duration of therapy. Patients often require long-term intravenous antibiotics.

Exposed bone, either by way of open fracture or subsequent wound breakdown, is virtually synonymous with osteomyelitis in a reconstructed limb, but does not necessarily call for radical excision. Bone scan and magnetic resonance imaging in conjunction with blood levels of erythrocyte sedimentation rate and C-reactive protein can be used to confirm a diagnosis of suspected osteomyelitis. The mainstay of surgical therapy for osteomyelitis includes thorough debridement of infected bone and necrotic tissue, appropriate antibiotic therapy, and closure of dead space with well-vascularized tissue. Bony defects from debridement may be treated with cadaveric bone grafting once bone and tissue cultures are negative. Larger bony defects may require vascularized bone grafting.

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Flap surgery (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Soft tissue loss – Soft tissue loss from the lower extremity can be due to trauma or surgery to treat infection, malignancy, degenerative disease, or congenital deformities. Successful flap reconstruction replaces this tissue and restores the appearance and function of the affected limb. (See 'Etiologies of soft tissue loss' above.)

●Lower extremity flap reconstruction – The process of soft tissue reconstruction is termed "coverage," which is accomplished using skin grafts or locoregional or free flaps based on the principles of the reconstructive ladder. A combination of reconstructive techniques may be required to provide optimal closure of a particular wound and surgeries may need to be staged. For lower extremity wounds, muscle flaps and fasciocutaneous flaps each have their own advantages. The approach to specific lower extremity wounds based upon their location is reviewed above. (See 'Soft tissue flap reconstruction' above and 'Reconstruction by location' above.)

●Flap monitoring and care – Postoperative care following lower extremity soft tissue reconstruction involves vigilant monitoring of any flap reconstruction using frequent examination and Doppler assessment of pulses. For microvascular reconstruction to the lower extremity, we initiate aspirin (325 mg orally each day), and continue aspirin postoperatively for two weeks, which is the period during which new vascular intima is forming across the anastomotic site. (See 'Postoperative care' above and 'Flap monitoring and wound care' above.)

●Venous thromboembolism prevention – Ongoing measures to prevent venous thromboembolism are important since most patients are immobilized on bed rest after their lower extremity reconstruction. Elevation of the lower extremity is useful for preventing edema accumulation in the soft tissues of the leg. (See "Surgical reconstruction of the lower extremity", section on 'Postoperative care' and 'Postoperative care' above and 'Flap monitoring and wound care' above.)

●Complications – Complications of flap reconstruction of the lower extremity include wound, flap necrosis, and sensory disorders. (See 'Complications' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Raymond Dunn, MD, who contributed to an earlier version of this topic review.