The treatment of burn-related wounds requires consideration of several factors, including defect size, available donor sites, exposure of critical structures, and the ultimate functional and aesthetic result of reconstruction. Although skin grafts and locoregional flaps are workhorses in burn reconstruction, they have inherent limitations that can directly impact reconstructive outcomes. Microsurgical free tissue transfer represents a viable option for the reconstruction of burn-related wounds in certain patients. Each anatomic region of the body has unique challenges that must be addressed to achieve a successful reconstruction. Therefore, the choice of free flap must be individualized to the wound and patients.
Key points
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Microsurgical free tissue transfer represents a viable option for reconstruction in burn patients when other options on the reconstructive ladder are not appropriate.
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Free tissue transfer can be performed during both the acute and reconstructive phases of burn patient care, however, with different sets of indications.
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The choice of free flap requires consideration of the specific anatomic region requiring reconstruction, the availability of donor sites, and its ultimate functional and aesthetic outcome.
Introduction
Comprehensive care of burn patients requires a diverse breadth of skills, beginning with initial evaluation, followed by resuscitation, timely excision, grafting, and closure. Sometimes, however, the nature of the injury exceeds the abilities of traditional methods for closure. In these scenarios, exposure of critical structures, such as bone, joint spaces, and/or significant neurovascular structures, requires something more complex. When the defect is sizable, regional pedicled flaps can be a great option. However, when pedicled flaps are not available because of the size and/or distribution of the burn injury, free tissue transfer may be required. This requirement can be true in the acute setting, when critical structures are exposed but also when functional deficits might otherwise require serial procedures with additive downtime and uncertain outcome. Patient care must be individualized, as patients with multiple comorbidities might be better served by serial minor procedures, whereas healthy patients might be better off with an initial free tissue transfer.
Free tissue transfer offers a unique treatment option with its ability to bring vascularized, composite tissue (skin, subcutaneous fat, fascia, muscle, and/or bone) to a given defect. This article focuses on the role of free tissue transfer in the acute and reconstructive care of burn patients.
Introduction
Comprehensive care of burn patients requires a diverse breadth of skills, beginning with initial evaluation, followed by resuscitation, timely excision, grafting, and closure. Sometimes, however, the nature of the injury exceeds the abilities of traditional methods for closure. In these scenarios, exposure of critical structures, such as bone, joint spaces, and/or significant neurovascular structures, requires something more complex. When the defect is sizable, regional pedicled flaps can be a great option. However, when pedicled flaps are not available because of the size and/or distribution of the burn injury, free tissue transfer may be required. This requirement can be true in the acute setting, when critical structures are exposed but also when functional deficits might otherwise require serial procedures with additive downtime and uncertain outcome. Patient care must be individualized, as patients with multiple comorbidities might be better served by serial minor procedures, whereas healthy patients might be better off with an initial free tissue transfer.
Free tissue transfer offers a unique treatment option with its ability to bring vascularized, composite tissue (skin, subcutaneous fat, fascia, muscle, and/or bone) to a given defect. This article focuses on the role of free tissue transfer in the acute and reconstructive care of burn patients.
Limitations of grafts/local flaps
One of the fundamental principles of reconstructive plastic surgery is to restore both appearance and function. This restoration is done by replacing the missing tissue components based on both the scope of what was lost and what is needed to achieve a safe, functional, and aesthetic closure. In the setting of most burn injuries, this presents as a deficiency of skin and subcutaneous fat in the setting of a wound that is also at risk for developing an infection from the loss of skin integrity. Depending on the size of the burn, the risk of infection can be small or pose a life-threatening problem. The reason this is important is that when the problem is defined by both the missing tissue components and what else is occurring with patients (eg, the clinical course, medical comorbidities, patient goals), it becomes apparent that surgical treatment must be individualized ( Fig. 1 ).
When considering the initial steps of the reconstructive ladder for burn patients, limitations are immediately recognized. When wounds are deep and expose muscle, skin grafts can be placed but result in a contour deformity. In situations whereby a seal can be achieved, the use of negative pressure wound therapy (NPWT) can help to both decrease the overall size of a wound and form granulation tissue that helps lessen the contour deformity. Other increasingly complex defects can include exposure of tendons with loss of paratenon. In these instances, the use of dermal replacements can help form a vascularized bridge over the exposed tendon permitting later coverage with a skin graft, even in multiple layers.
Although these techniques do work and minimize surgical morbidity, they may require significant additional time to achieve closure and have some pertinent limitations in burn patients. NPWT requires intact skin to achieve a seal and maintain suction, which can be problematic for burn patients. Additionally, when NPTW spans across joints, it can limit mobility for patients and make it challenging for physical and occupational therapists to treat the covered areas ( Fig. 2 ). With dermal replacements, the challenge is that they are avascular and at increased risk of infection as they await vascularization.
As one progresses further up the reconstructive ladder, local flaps can be tremendously helpful in both the acute and reconstructive setting. Fasciocutaneous flaps tend to more closely replace what is lost in a burn injury, such as a reverse radial forearm flap to cover a dorsal hand wound. In an acute setting, muscle flaps can be lifesaving, such as a pectoralis major flap that is rotated to cover the great vessels in the neck or the axillary vessels on the proximal arm or a gastrocnemius muscle flap to cover the patella of an exposed knee joint ( Fig. 3 ). Although pedicle flaps have a role, they are limited based on the pattern of the burn injury and sometimes do not ideally address the defect. It is for these reasons that free tissue transfer retains a role in both acute and delayed burn reconstruction.
Microsurgical indications for burns
Acute Injury Phase
With a large (>20% total body surface area [TBSA]) burn injury, there are often many things occurring simultaneously that have a significant impact on flap outcomes. There are massive fluid shifts that occur during the acute resuscitation and during large excision and grafting procedures. Additionally, debridement of nonviable tissue will lead to the potential for local and/or systemic infections, which can lead to microvascular thrombosis from both local inflammatory effects as well as systemic hypotension. Systemic infections from pneumonia, hypovolemia related to acute kidney injury requiring dialysis, rhabdomyolysis from electrical injuries, blood loss requiring multiple transfusions, and a stress response that can adversely impact glycemic control represent a small list of reasons why one would want to avoid a free flap in the acute setting. In this setting, every effort to minimize controllable risk factors must be made before considering an acute free tissue transfer.
There are times, however, when devastating injuries occur that do not fit into the aforementioned scenarios seen in higher TBSA burns. Usually these are the result of deep flame or electrical injuries. In this scenario, there are reports of acute burns being treated with free flaps. In a small series from Utah on electrical burns, they successfully treated 4 patients who required 5 free flaps for their reconstruction. They were debrided aggressively and subsequently covered with acute free flaps. Although outcomes were limited, 3 of 5 of the patients were returned back to “gainful employment.”
In terms of timing of reconstruction, the data again are limited to single-center retrospective reports. In one article from Germany reviewing their experience with 75 free flaps in 60 patients, they found that flap loss rates were temporally related to the time performed in patients with deep flame (n = 49) and electrical burns (n = 26). They experienced a 13% (n = 10) flap loss rate whereby 8 of 10 occurred between 5 and 21 days and all 10 occurred between 5 and 42 days. The investigators noted that they had no flap losses when they were performed at times greater than 6 weeks. In another publication from India, they demonstrated a 92% success rate in treating electrical burns 1 to 21 days after injury, with their one failure occurring on the third day with a free gracilis flap. Another injury pattern potentially amenable to immediate reconstruction is the deep thermal or electrical injury of the head and neck with exposed critical structures, such as calvaria with nonviable outer table, loss of the orbit, and other full-thickness defects that expose critical structures. Although the collective data are limited on ideal timing, patients should be optimized medically and surgically before free tissue transfer.
In the acute setting, free tissue transfer wound closure is typically prioritized over function and cosmesis. Nevertheless, it is important to consider functional and aesthetic concerns, as it is usually possible to incorporate them into the overall surgical plan. For example, a full-thickness cheek defect could be reconstructed with a fasciocutaneous flap, but a neurotized myocutaneous flap might be considered to restore facial nerve function ( Fig. 4 ).
Another important consideration in the acute setting is the inflammatory state of patients and its impact on the integrity of the tissue and patency of the anastomosis. Although the evidence regarding antiplatelet therapy and anticoagulation in this setting is inconclusive, it may be a consideration based on the prothrombotic state of acute burn patients. There are data to suggest that normothermia is beneficial, volume replacement between 3.5 and 6.0 mL/kg/h is helpful, vasopressors are not harmful to outcomes, and that dextran should be avoided.
Reconstructive Phase
After the acute injury phase has passed, wounds have been closed, and the inflammatory response has subsided, burn scars can then be assessed for possible reconstruction. The hypermetabolic response to a large burn can persist for up to 36 months after the initial injury and may impact outcomes of complex reconstructive procedures due to a prothrombotic and catabolic state. Once patients have passed beyond this phase, free flaps reenter the reconstructive paradigm and can be used to address a variety of aesthetic and functional problems. Options include flaps such as functional muscle transfers, chimeric flaps, and prelaminated flaps depending on the clinical scenario ( Fig. 5 ).
