Continuing Education Activity

The ability to transfer flaps is a critical skill reconstructive surgeons use to close many different types of tissue defects, ranging from small skin-only defects to large, composite tissue defects. These defects may be caused by traumatic, oncological, or congenital processes, and surgeons must understand how the etiology and anatomy involved affect the selection of the appropriate reconstructive option. This activity outlines the evaluation and management of tissue defects using flap transfer and highlights the role of the interprofessional team in the care of these patients.

Objectives:

• Outline the management considerations for patients with tissue defects.
• Explain the importance of adequate patient counseling and collaboration when planning flap transfer.
• Summarize the common pitfalls of flap design.
• Describe the importance of collaboration and communication within the interprofessional team to enhance care delivery for patients undergoing flap transfer.

Introduction

Flap design and transfer for the closure of tissue defects that cannot be sutured primarily is a fundamental skill in the practice of reconstructive surgery. Because of the incredible breadth of tissue defects, one may encounter in a patient - small, skin-only defects up to large, multi-tissue-type defects - as well as the wide range of etiologies, such as traumatic, oncological, and congenital, the ability to transfer flaps requires a diverse set of competencies that must constantly evolve as new techniques are described, and new mechanisms of injury emerge. Understanding the anatomy and physiology of both the defect and potential donor sites is critical to successful flap transfer, as is mastery of atraumatic soft tissue surgical technique. Ultimately, flap design and transfer represent the clinical intersection of the science of medicine and the art of surgery, which renders these procedures either immensely rewarding or singularly frustrating, depending on the outcome.[1]

Anatomy and Physiology

Flaps may be classified in several ways, depending upon blood supply, tissue type, and distance of the harvest site from the tissue defect. Each of these schemes has its own set of anatomical and physiological implications.

When classified according to blood supply, flaps are generally divided into "random" and "axial" categories. So-called "axial" flaps are flaps in which the blood supply is based upon a named artery that courses longitudinally within the flap; venous drainage occurs primarily through the veins that correspond to the named artery. To improve survivability, an axial flap will typically include tissue from a single angiosome only, which is a region of tissue supplied predominantly by a single named blood vessel. In some cases, a flap may include tissue from more than one angiosome despite having only one named artery within the vascular pedicle (the base of the flap that contains the arterial supply and venous drainage). In these cases, the reliability of the flap may be questionable unless the flap is delayed prior to inset. Delaying a flap is the practice of elevating it by incising around it and lifting it away from the surrounding tissue, but then replacing it into its native position rather than transferring it into a defect.[2]

This approach permits choke vessels between angiosomes to open, thereby improving the blood flow throughout the flap before stressing its vascular supply by twisting and stretching the pedicle, which frequently happens when the flap is inset into ta defect. The classic example of a flap that includes multiple angiosomes is the deltopectoral flap, which is based upon intercostal perforating arteries branching off the internal mammary artery.[2] "Random" pattern blood supply flaps, on the other hand, derive their perfusion from the subdermal vascular plexus, a low-pressure system that is prone to compromise when the flap is twisted or stretched excessively. Because the blood supply is more tenuous in random pattern flaps, it is generally recommended that these flaps should not be designed with a length to width ratio of more than 3 to 1.[3]

Flaps may also be described according to tissue type involved, with the tissue types incorporated in the flap typically corresponding to the tissue types missing from the defect, following Sir Harold Delf Gillies' injunction to "replace like with like." Most smaller flaps will be of the cutaneous variety, but mucosal, bony, muscle, and fascia-only flaps are also common. Larger defects often require "composite" reconstruction (multiple tissue types together), potentially including fasciocutaneous, myocutaneous, and osteocutaneous flap transfers. Classic examples of composite tissue transfer include the radial forearm free flap, the pectoralis major flap, and the fibula free flap, respectively. Human composite tissue allograft transfer, such as hand or face transplant, also falls into this category.[4]

Perhaps most practically, flaps are often categorized by the distance between the donor site and the tissue defect. Flaps harvested from distant sites removed entirely from the body, inset into their defects, and then have their vascular supplies reconstituted via microsurgery are referred to as "free" or "microvascular" flaps. These are frequently composite flaps with more than one tissue type, and they are always axial in design. Common examples include the anterolateral thigh flap, the iliac crest flap, and the gracilis flap. When flaps are harvested from the same region as the defect, such as the same limb or elsewhere in the head and neck, but the donor site does not directly border the defect, and the flap does not need to be entirely removed from the body, the flaps are known as "regional." Regional flaps are also generally axial in design but may or may not contain composite tissue.[5] 

Classic examples include the paramedian forehead flap, the temporoparietal fascia flap, and the gracilis flap. It is worth mentioning that several flaps, particularly muscular flaps like the trapezius and latissimus dorsi flaps, can be transferred as either free flaps or as regional flaps, depending upon the configuration and location of the defect relative to the flap harvest site. While free flaps tend to be employed for the closure of larger defects (approximately 30 cm^2 or greater), regional flaps may cover large or small defects.[5] 

Lastly, a local flap is a flap whose donor site lies immediately adjacent to the tissue defect and therefore becomes a part of the defect during closure. For this reason, an additional consideration when transferring local flaps is the anticipated configuration of the final scar and the optimal means of hiding it in aesthetic subunit boundaries, such as the nasolabial fold or the hairline, or aligning it within relaxed skin tension lines or wrinkles. Local flaps generally rely on random pattern blood supplies, and they tend to be employed for smaller defects; they most often contain cutaneous or mucosal tissue only. These flaps are further categorized based on the type of movement the flap in question must undergo to close the defect. The four types of movement are advancement, rotation, transposition (in which the flap and other normal tissue adjacent to the defect trade places), and interpolation (in which the flap traverses either over or under normal tissue to reach the defect). In practice, interpolation is more frequently used in regional flaps than in local flaps, and rotation is commonly employed along with rotation to effect the closure of many defects.

Indications

Flap transfer is indicated when a tissue defect cannot be closed primarily, and it would be inappropriate to allow the defect to heal by secondary intention or with the use of a skin graft. When substantial tissue loss occurs during trauma or as a result of oncologic resection, flaps are often employed for wound closure. Classic examples include traumatic scalp avulsions requiring closure with latissimus dorsi free flaps or hemiglossectomies requiring reconstruction with radial forearm free flaps.[6][7]

Contraindications

Flap transfer for defect closure is contraindicated when the defect can be safely, aesthetically, and effectively closed primarily or with a skin graft, when there is an active infection in the wound, and when there is residual malignancy after oncologic resection. Flap transfer may proceed once the infection has resolved and/or the margins have been cleared. In palliative care cases, positive oncological margins may not necessarily contraindicate flap transfer.

Equipment

Equipment requirements vary greatly depending on the type of flap to be transferred. Local flaps may require no more than fine soft-tissue instruments and local anesthesia, while larger regional and free flaps may require extensive instrumentation, including soft tissue sets, bone saws, an operating microscope, microvascular tools, and vasoactive medications.

For the average in-office local flap case, e.g., Mohs defect closure, the following may suffice:

• Scalpel (#15 Bard-Parker blade or #6700 beaver blade)
• Forceps (Adson-Brown or 0.5 mm Castroviejo)
• Needle holder (Halsey or Castroviejo)
• Dissecting scissors (iris or Kaye blepharoplasty)
• Suture scissors
• Electrocautery (monopolar or bipolar)
• Suture (5-0/6-0 polypropylene, 4-0/5-0 poliglecaprone)
• Adhesive strip tapes
• Skin marker
• Local anesthetic (1% lidocaine with 1:100,000 epinephrine)
• Antiseptic scrub solution (povidone-iodine or isopropanol)

Personnel

Just as with equipment, personnel requirements will vary according to the demands of the case, but at minimum, a surgeon and nurse will be needed; for larger cases, an anesthesia provider, a surgical technologist, and a surgical first assistant will be present. Postoperatively, nursing and physical therapy may be required as well, particularly if the defect and/or donor site are located in a limb.

Preparation

Preoperative considerations should include:

1. Smoking history
2. Atherosclerosis
3. Peripheral vascular disease
4. Steroid use
5. Diabetes
6. Previous surgeries
7. The extent of the defect
8. Patient age and skin condition
9. Defect location.[1]

Before free or regional flap transfer, a preoperative angiogram may help evaluate circulation and angiosome anatomy. Because larger defects often require more complex reconstruction, and more complex reconstruction often requires more time to complete, ensuring the patient has had the appropriate medical preoperative evaluation can mean the difference between a good outcome and a catastrophe. When flap transfer is planned carefully, paying attention to both the technical aspects of the procedure and the patient's overall health and functional/aesthetic goals, outcomes are generally very satisfactory.[8]

Technique

When determining the appropriate flap to use for the closure of a defect, surgeons often think through a construct known as the "reconstructive ladder," which serves to enumerate the options from least invasive to most complex. The reconstructive ladder also includes options not strictly classified as flaps, but that are nevertheless important techniques commonly employed for tissue reconstruction.

The Reconstructive Ladder (the simplest options begin at the bottom, and the list progresses in complexity towards the top):

• Composite tissue allograft (transplant)
• Free flap transfer
• Regional flap transfer
• Local flap transfer (may include tissue expansion)
• Skin and composite graft transfer (full thickness or split thickness)
• Delayed primary closure
• Primary closure
• Healing by secondary intention

Free Flap Technique

Free tissue transfer techniques vary considerably depending upon both the type of flap and surgeon preferences. Primary considerations include ensuring the flap contains the correct tissue types in appropriate amounts and that the vascular pedicle is long enough to reach the recipient vessels that will perfuse the flap. Because only a single angiosome is usually harvested as a free flap, it is important to ensure that the entirety of the harvested tissue will be perfused adequately by the vessel harvested in continuity with the flap.[9]

Some flap harvest techniques involve identifying and dissecting the vascular pedicle before elevating the flap itself, for example, the gracilis flap, and others, such as the radial forearm flap, begin with the elevation of the flap, and vascular dissection occurs afterward.[10][11] 

Once the flap is harvested, a clock to keep track of ischemia time is usually started so that the surgeons know how long the tissue has been deprived of blood flow; every attempt to minimize ischemia time should be made. The flap is then usually inset either partly or completely prior to the microsurgical anastomosis of the blood vessels to ensure the geometry of the vascular pedicle is correct, and it will not be stretched or twisted during the closure of the defect. Microsurgical anastomosis requires an operating microscope and microsurgical instruments, as well as 8-0 to 10-0 suture, and frequently venous couplers as well. In cases of buried flaps, a monitor paddle may be brought to the skin to facilitate postoperative monitoring, or an implantable Doppler probe may be used for real-time evaluation of blood flow.

Correct pedicle geometry is critical for maintaining flap perfusion, particularly the prevention of venous outflow obstruction. The first three postoperative days are when the freshly sewn vessels are most likely to fail and result in flap death because it takes approximately 72 hours for the vessel endothelia to heal over the sutures. During this time, frequent "flap checks" are often required so that if a vascular insult does occur, the patient may be returned to the operating room for prompt wound exploration and flap revision, if necessary. After that, the risk of flap failure steadily decreases until neovascularization has taken place and rendered the original vascular pedicle less critical for flap survival, roughly two to three weeks postoperatively.[12] Because free flaps are often quite large, the need for secondary reconstruction of the donor site is common, and this is typically accomplished with a split-thickness skin graft.

Regional Flap Technique

Regional tissue transfer may be performed similarly to free tissue transfer; indeed, several flaps may be transferred as either regional or free flaps (radial forearm, gracilis, trapezius, latissimus dorsi, temporoparietal fascia, strap muscle, etc.). The same considerations of tissue type and volume apply to regional flaps that apply to free flaps, and the techniques are just as variable. The primary difference between regional and free flaps is that regional flaps maintain a consistent blood supply throughout the operation and are never completely separated from the body; they are generally considered interpolated flaps. Regional flap vascular pedicles are therefore vulnerable to stretching and twisting, although they are not nearly as tenuous as free flaps during the first 72 postoperative hours. Regional flaps tend to require significant twisting of their vascular pedicles by virtue of the donor locations relative to the most common recipient sites; classic examples include the paramedian forehead flap and the pectoralis myocutaneous flap, and the supraclavicular artery island flap.[13][14][15] 

Advantages of regional flaps over free flaps are reliability, lack of requirement for microsurgical equipment, decreased time requirement in the operating room (and therefore increased safety in patients with multiple comorbidities), and the ability to elevate and delay the flap for approximately two weeks preoperatively to improve survival rates.[16] However, as with free flaps, the harvest site may require secondary reconstruction with skin grafting.

Local Flap Technique

Local flaps, by definition, consist of tissue that lies adjacent to the defect; to reach their destinations, they may be advanced, rotated, transposed, interpolated, or any combination thereof.[3][17][18][19] Classic examples include O-H flaps, O-Z flaps, rhombic and bilobed flaps, and melolabial flaps, respectively. Unlike regional and free flaps, local flaps tend to have random pattern blood supplies, which means that there is no vascular pedicle per se, but rather that the subdermal plexus supplies oxygenated blood and provides venous drainage. The base of the flap, which connects the flap to the surrounding tissue, should be accorded the same respect as a vascular pedicle; stretching and twisting are avoided.

Likewise, because these flaps are perfused solely by microvasculature, the tissue should be handled very carefully, elevation should be performed meticulously and in the correct plane, and the use of electrocautery should be minimized. The correct plane of elevation will depend on the area of the body, but it is typically subdermal. In the scalp, a subgaleal plane is often preferred; however, and on the nose, a supraperichondrial plane is frequently used. In general, local flaps should be designed such that the length does not exceed three times the width of the base; otherwise, the distal tip of the flap is likely to suffer vascular insufficiency, particularly if the base needs to twist for flap inset.[3]

To close both the primary tissue defect and the secondary defect (where the flap was harvested), wide undermining for up to 2 to 4 cm should be performed, taking care to avoid disrupting sensitive structures in the area (eyelids, nostrils, etc.).[20] An important exception to this undermining suggestion is the use of V-Y advancement flaps because undermining these flaps will result in vascular insufficiency. However, for most other cases, the undermining should be completed, and tacking sutures may be placed before incisions or Burow's triangles are made. A Burow's triangle is a wedge of skin removed from the base of a flap to flatten a standing cutaneous deformity that arises when a flap is rotated and/or advanced, particularly when a flap is rotated more than 90 degrees. These excisions can be placed in locations where their scars are least likely to fall outside of relaxed skin tension lines or aesthetic subunit boundaries.[17]

Relaxed skin tension lines and aesthetic subunit boundaries are critical considerations for local flap design; while the defect size and location are not usually planned, it is critical to laying out the flap in such a way that transfer does not cause distortion of any nearby structures (lips, ears, hairline, etc.) and that its scars will fall as closely as possible into aesthetic subunit boundaries and relaxed skin tension lines.

Complications

Flap transfer complications can generally be divided into donor site and flap issues and further separated into acute and chronic complications. Donor site problems include bleeding and infection acutely, as well as scarring and functional loss, such as gait disturbance or hand contracture, on a longer-term basis. Each donor site will have specific complications unique to it; other examples include abdominal hernia from iliac crest free flap harvest, pathological wrist fracture from osteocutaneous radial forearm free flap harvest, and foot drop from peroneal nerve injury in fibula free flap harvest.[21][22]

Complications associated with the flap itself predominantly involve acute compromise of the flap's blood supply and subsequent failure of the reconstruction. Generally, the larger the defect, the more significant the consequences of flap death.[23] 

When flaps do die, it is usually a result of vascular compromise, most often obstruction of the venous outflow.[12] In free flaps and larger regional flaps, this is often caused by a clot in the vein primarily responsible for flap drainage; in local flaps, the venous aspect of the subdermal plexus is affected. The subdermal plexus is sensitive to excessive tension or torsion, and when the width or quality of the tissue is insufficient to support adequate blood flow, the flap will die either partially or completely. Typically, if a flap survives for the first postoperative week without displaying any signs of either venous obstruction (duskiness or firmness) or arterial insufficiency (pallor and coolness), it will likely remain viable.

One of the more common causes of vascular insufficiency is compression from a hematoma; if identified, it should be evacuated promptly. If a vascular problem arises in a free flap, the microvascular anastomosis can be revised in the hope of improving blood flow. If vascular insufficiency occurs in regional or local flaps, the inset may be revised to decrease tension or torsion on the pedicle. In cases of venous obstruction in any flap, medicinal leeches may represent a temporary solution while the flap reestablishes venous outflow. When leeches are applied, it is important to administer a fluoroquinolone antibiotic, such as levofloxacin, to prevent infection with Aeromonas hydrophila, a Gram-negative bacillus commonly found in leeches.[24]

Numerous factors may increase the risk of early flap failure, including infection, inadequate blood pressure, nutrition status, and many others.[25] Chronic flap complications may be either functional or aesthetic in nature and include scarring, contracture, color/texture mismatch, hair growth or lack thereof, numbness, and pain.

Clinical Significance

Flap transfer has been a foundation of reconstructive surgery for potentially as long as 3,000 years since the Sushruta Samhita described the use of forehead flaps for nasal defect closure.[26] While the techniques have evolved significantly over the intervening millennia, the concept of reconstructing the human body using tissue that appears and performs similarly to the missing tissue remains the same. A well-designed flap should use the minimal amount of tissue required, cause the least amount of donor site morbidity, and maximize the return of form and function to the tissue defect, while simultaneously optimizing the survivability of the flap to obviate the need for revision surgery in the future. The astute reconstructive surgeon will maintain familiarity with a wide range of flap transfer options to suit a wide range of defect tissues and sizes to enhance patient outcomes. 

Enhancing Healthcare Team Outcomes

Flap transfer requires an interprofessional team consisting of surgeons, primary care providers, nurses, anesthesia providers, and physiotherapists. Safe and effective reconstruction of the broad range of tissue defects that one may encounter necessitates familiarity with an accordingly broad range of reconstructive options; patients with extensive defects will require careful preoperative evaluation, intraoperative management, and postoperative rehabilitation.