Alloplastic Materials

Introduction

Advances in medical technology have allowed plastic surgeons to utilize synthetic materials as an alternative to autologous tissues when performing many of today’s aesthetic and reconstructive surgeries. Although autologous materials are generally preferred, synthetic materials provide several advantages over tissues obtained from the patient:

• Not resorbed over time (unless they are designed to do so)
• Do not require a second surgical donor site
• Provide more material than can often be obtained from the patient
• Can be custom-tailored to the individual patient
• Reduce operating time since graft harvesting is not performed

Because of the many benefits to using alloplastic materials, there is currently a strong interest in developing the ideal implant material which would possess the following characteristics: it should (1) be chemically inert; (2) be incapable of producing hypersensitivity or a foreign body reaction; (3) be easily contoured; (4) retain stable shape over time (except when desired); (5) be noncarcinogenic; (6) become ingrown or replaced by living tissue; (7) be easy to remove and sterilize; and (8) not interfere with radiographic imaging. Despite much effort and ingenuity, creation of the ideal implant material has yet to be accomplished. However, various alloplastic materials are being used today in plastic and reconstructive procedures, and many of them have proven quite promising.

Pre- and Intraoperative Considerations
The vascularity of the recipient site and the ability to provide sufficient soft tissue coverage of the implant must be assessed preoperatively. Decreased vascularity secondary to scar tissue (from previous surgeries) or radiation impairs the establishment of normal fibrovascular tissue encapsulation and may interfere with the normal inflammatory response if the implant were to become infected.

In order to prevent implant exposure or extrusion, soft tissue coverage over an implant should be as thick as possible. The size of the implant should be comparable to that of the tissue pocket or wound cavity in order to avoid tension of the overlying soft tissue, and the implant should be fixated to a stable adjacent structure to prevent migration of the implant. All patients should receive perioperative intravenous antibiotics followed by a postoperative oral course, although the optimal antibiotic choice and duration have yet to be determined for most implants. What is clear is that intraoperative handling of the implant should be minimized in order to prevent bacterial transmission, and strict adherence to sterile technique is essential.

Classification of synthetic materials used in plastic and reconstructive surgery
Silicone-based materials:	BioPlastique Injectable silicone Silastic sheets Silicone Silicone gel
Polytetrafluoroethylene:	Gore-Tex Proplast I and II Teflon
High density polyethylene:	Medpor
Polymer mesh:	Dacron (Mersilene) Dexon Prolene Supramid Vicryl
Biological glasses:	Bioactive glasses (Bioglass) Glass ionomer
Tissue adhesives:	Cyanoacrylate
Acrylics:	HTR Polymer Methylmethacrylate

Choice of Alloplastic Material
The type of procedure as well as the size and character of the defect being augmented often dictate the type of implant material. In the preantibiotic era, inert materials such as gold, silver, platinum and paraffin were used with little success and were quickly abandoned. Currently, there are numerous implantable materials being used today (Table 14.1). These materials are used in a wide range of procedures, such as aesthetic procedures, craniofacial surgery, maxillofacial trauma, breast reconstruction and hand surgery. Table 14.2 lists the common uses for the various allopastic implants.

Silicone
Silicone-based prosthetics have been used as medical implants since the 1950s due to their chemically inert nature, resistance to degradation, and lack of significant allergic reactions. Silicone is useful for a variety of aesthetic surgeries, complex contouring and reconstructive procedures. Silicone comes in the form of silicone gels, silicone rubber or solid silicone implants. Silicone gels can provide a more natural feel, as seen with breast implants, but the risk of rupture requiring capsulectomy is a distinct disadvantage. The use of silicone gel has been surrounded by controversy related to concerns about migration, toxicity and an unproven association with systemic disease, leading to restriction of the use of silicone gel implants by the FDA in 1992. This ban was recently lifted after an extensive unbiased review by the Institutes of Medicine. Silicone rubber is used for tissue expanders, the outer shell of both saline-filled and silicone gel-filled breast implants, and as an onlay material for the augmentation of the bony skeleton and soft tissues. However, silicone rubbers are relatively weak and tend to tear, leading to implant failure. Solid silicone implants are commonly used for chin and malar augmentation, and have been used in nasal, chest and calf augmentation, as well as in joint replacement and tendon reconstruction.

A list of the procedures that commonly employ allopastic materials
Procedures	Materials Used
Cranioplasty and forehead augmentation	Glass ionomer and bioactive glass Hard-Tissue-Replacement (HTR) polymer Methylmethacrylate Medpor Poly(L-lactide) and polyglycolic acid plates and screws Silicone
Anterior mandibular augmentation	Medpor Polyamide mesh Silicone
Mandibular body and angle augmentation	Glass ionomer and bioactive glass Medpor Methylmethacrylate Poly(L-lactide) and polyglycolic acid plates and screws
Malar and maxillary reconstruction	Glass ionomers Gore-Tex Medpor Methylmethacrylate Polyamide mesh Silicone Teflon
Zygomatic reconstruction	Glass ionomers Medpor Gore-Tex Poly(L-lactide) and polyglycolic acid plates and screws Silicone
Orbital reconstruction	Gore-Tex HTR Polymer Medpor Poly(L-lactide) Silicone Teflon
Ear reconstruction	Medpor Silicone
Tendon repair	Gore-Tex Cyanoacrylate
Soft tissue augmentation	BioPlastique Gore-Tex
Breast augmentation and tissue expansion	Silicone (saline or silicone gel filled)
Wound repair and scar revision	Cyanoacrylate Silastic sheets
Chest and abdominal wall reconstructions	Dacron mesh Gore-Tex Prolene mesh Vicryl mesh
Nasal augmentation	Gore-Tex Polyamide mesh Silicone

Because silicone is not porous, tissue ingrowth does not occur. A fibrous capsule forms around the implant that is relatively avascular and can contract which may lead to implant migration. This avascular capsule is a potential space for infection and in the setting of infection may require removal of the implant.

BioPlastique
BioPlastique® is a nonbiodegradable, relatively inert injectable liquid used for soft tissue augmentation. The textured surface of the particles allows for tissue ingrowth, and the particle size is large enough to prevent engulfment by macrophages but small enough to become encapsulated within 3 to 6 weeks. Studies on the use of BioPlastique demonstrate good-to-excellent results in augmenting small defects on the dorsal nose, malar area, cheeks and chin with no adverse immunologic reactions. Although the clinical results with Bioplastique have been encouraging, it is not FDA approved at this time.

Polymethylmethacrylate
Polymethylmethacrylate (PMMA) is an acrylic polymer used as a bone substitute in plastic surgery and neurosurgery. PMMA is radiolucent, extremely durable and completely biocompatible, making it a widely used material for cranial bone reconstruction-alone or in combination with wire or mesh reinforcement. When powdered granules of methylmethacrylate polymer are mixed with methylmethacrylate liquid monomer, a moldable dough forms as the monomer polymerizes and hardens in about ten minutes. Near the end of the polymerization process, an exothermic reaction occurs that can potentially damage the local tissues, the major complication associated with the use of PMMA. This can be avoided by continually irrigating the implant bed with cool saline during the polymerization. A rare, but serious complication is the inadvertent entry of the PMMA into the venous or arterial systems. If this occurs it can cause complete heart block, cardiac arrest and other arrhythmias. This complication is most often seen during orthopedic procedures where PMMA is used for joint replacements or fracture repair. Hard-tissue-replacement (HTR) polymer is a porous form of PMMA that allows for fibrous ingrowth, leading to an implant that is nonresorbable and very stable. Applications for HTR include chin and malar augmentation, with potential for additional uses in craniofacial reconstruction.

Polyester (Dacron®, Mersilene®)
Polyethylene terephthalate (Dacron) is a biocompatible, flexible, nonabsorbable polymer that is used as a suture material, as a prosthetic material for arterial replacement, and as a mesh (Mersilene) in abdominal and chest wall reconstruction. Its use has also been described for chin and nasal augmentation. Biodegradable Polyester (Polyglycolic Acid, Poly-L-lactic Acid) Polyglycolic acid (PGA) and Poly(L-lactide) (PLLA) are polymers that are degraded in the body at physiologic pH over the course of weeks to months. These resorbable polymers are available as mesh sheets for body wall reconstruction and as rods for the internal fixation of fractures and osteotomies. They have also been fashioned into resorbable miniplates and screws for the fixation of bones of the craniofacial skeleton. Although they do not appear to have any cytotoxic effects, they do provoke an inflammatory or foreign body response after implantation.

Polyamide Mesh (Supramid®, Nylamid®)
Polyamide mesh is a woven, polymer mesh implant that is biocompatible, can be easily shaped and sutured, allows for fibrous tissue ingrowth, and has been used for the repair of orbital floor defects. It seems to be well tolerated and has a low rate of extrusion, even in areas of thin skin such as the nasal dorsum. However, polyamides do undergo resorption and induce an inflammatory response, making their use in facial augmentation and reconstruction somewhat limited.

Porous Polyethylene (Medpor®)
Medpor is a high-density, porous polyethylene implant used frequently in facial surgery because it is nonantigenic, nonallergenic, nonresorbable, highly stable and easy to fixate. In addition, Medpor is available in a wide variety of preformed shapes for its use as a malar, chin, nasal, orbital rim, orbital floor and cranial implant, as well as an auricular framework in postburn ear reconstruction. Overall, complications of Medpor, such as exposure or infection, are rare.

Polytetrafluoroethylene (Teflon®, Gore-Tex®, Proplast®)
Polytetrafluoroethylene (PTFE) is an inert and highly biocompatible polymer that is extremely useful in soft tissue augmentation but has limited use in bony repair due to its low tensile and compressive strength. Teflon, the first PTFE graft to be used in plastic surgery, is a chemically inert polymer used for soft tissue augmentation in the past, but the main application for Teflon has been orbital floor reconstruction. Gore-Tex is a pliable, durable, inert, biocompatible material that has some tissue ingrowth, little inflammatory reaction and almost no encapsulation. In addition to being used in abdominal fascial reconstruction, chest wall reconstruction and soft tissue reconstruction, Gore-Tex has also been utilized for lip, nasal, chin and malar augmentation. It has also been utilized for the treatment of nasolabial and glabellar creases. Proplast I is a highly porous, black graphite/PTFE composite with a spongy consistency. Because Proplast I led to discoloration of the surrounding soft tissues when implanted, Proplast II-a more rigid, white PTFE/alumina compound-was developed as an alternative. Proplast, with a wide variety of applications including the reconstruction of the chin, zygoma, orbital rim, maxilla, mandible, skull and rib cage, was originally regarded favorably. However, reports of biomechanical failure, intense inflammation, infection and extrusion related to the Proplast temporomandibular joint implant, led to the removal of all Proplast implants from American markets by the FDA in 1990.

Calcium Phosphate Ceramics
Calcium phosphate implants have been available as bone replacement/augmentation materials for 20 years. The primary calcium phosphates in clinical use are hydroxyapatite and tricalcium phosphate. These materials are osteoconductive (providing a scaffold for bone ingrowth) thus allowing for integration into the recipient site after placement. As a result, calcium phosphates are very well tolerated with essentially no inflammatory response, minimal fibrous encapsulation, and no adverse effects on local bone mineralization.

Metals
Metals have been used for the past 35 years for skull reconstruction and repair, in addition to reconstruction of craniofacial and upper extremity skeletal injuries. Stainless steel, cobalt-chromium (vitallium), pure titanium and titanium alloys are the principal metals currently available. Characteristics of a desirable metal implant include biocompatibility, strength, resistance to corrosion and imaging transparency.

Postoperative Considerations
Although numerous potential complications may occur with any implant-related procedure (e.g., migration, extrusion, palpability), the one common denominator shared by all alloplastic implants is their inherent risk of infection. The majority of postoperative infections appear within weeks to months after the initial surgery. Low-grade infections manifested only by fevers and signs of mild cellulitis are managed by intravenous antibiotics. More serious infections involving wound breakdown, implant exposure, gross purulence or systemic spread of the infection require prompt removal of the implant as antibiotics and drainage alone are usually insufficient. Reimplantation should not be performed for at least 3 to 6 months to allow for complete treatment and resolution of both the infection and the inflammation in the surrounding tissues. Several studies suggest that smooth, nonporous, nonresorbable implants have lower rates of infection, but it remains to be seen whether any true infectious risk differences exist among the various alloplastic implant materials available today.

Pearls and Pitfalls

• Incisions should be placed as far as possible from the final position of the implant. This will decrease the risk of implant exposure or extrusion in the setting of a minor wound infection.
• The implant should be covered with as much soft tissue as possible. The pocket should be of adequate size; too large and the implant will shift position, too small and the implant will be at risk for extrusion due to tension on the closure.
• Whenever possible, always try and close a second layer of tissue between the skin and implant. This is critical if the implant lies directly beneath the incision.
• Implants with sharp corners should be smoothed down, since sharp edges can erode through the skin with time.
• The implant should be touched as little as possible. Clean, powder-free gloves should be worn and instruments should be used to handle the implant whenever feasible. The risk of infection and abnormal capsule formation is increased by the presence of any bacteria or foreign material on the implant.
• Do not use an implant composed of a rigid material to replace soft, pliable tissue.
• Keep an organized registry of all alloplastic implants in the event that the device fails or has to be removed. Give the patient a copy of the device name, model, manufacturer and serial number, in case failure occurs in the care of another physician.

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Microvascular Surgical Technique and Methods of Flap Monitoring

Introduction

The hand is capable of coordinated activity finer than the eye can direct. With the aid of magnification, the true capability of the hand can be exploited. As a tool for the plastic surgeon, microsurgery has allowed reconstructions that were simply not possible before. However, microvascular free tissue transfer is not a technique for the occasional microsurgeon. The catastrophic complication of flap failure looms over every microsurgical case; therefore, expertise in the execution of a free flap as well as its postoperative surveillance is key to a successful outcome.

Experience has shown that flap loss is a preventable complication and that elective microsurgery should have a failure rate of less than 2%. Most cases of flap loss are technical in nature. The fault may lie in the choice of flap, the harvest of the flap, preparation of donor vessels, insetting of pedicle or microsurgical technique. In general, it is best to think of all possible errors as additive in the process of thrombosis. Failure will occur if the procoagulatory factors outweigh the intrinsic ability of the vessels, in particular intact and uninjured intima, to prevent clot formation.

Flap Choice

The first step for success in microsurgery is flap choice. The specifics of different flaps are discussed in subsequent chapters. The most important determining factors for flap choice should be the surgeon’s experience and the goals of reconstruction.

In general, each surgeon should identify at least four flaps they feel comfortable with. These flaps should include a bulky muscle flap, a bulky fasciocutaneous flap, a thin fasciocutaneous flap, and a bone flap. With this armamentarium, the reconstructive surgeon will have tools that can be applied to most situations. By limiting himself to a small number of flaps, more experience can be obtained with each one. This increased experience translates to increased success. It is not advantageous to explore every novel flap that is reported, as this dilutes the experience and increases the chance of failure. With increasing experience with each flap comes increasing success and a lower failure rate.

This does not imply that specific flaps may not be beneficial over others in certain situations. There is no doubt that the donor properties of a latissimus dorsi flap differ from those of the gracilis flap and that each may be a better choice for a specific patient. However, the patient is best served with successful reconstruction. If there is significant benefit in a flap where the surgeon has no experience, the surgeon should consider referral or should seek additional training in order to add that flap to his or her armamentarium. This may include time in a cadaver lab or observing a surgeon with a particular skill.

Having mastered the tools of reconstruction, the surgeon should judiciously consider the requirements for reconstruction. Bulky muscle flaps are best for contaminated defects and bony injuries with high risk for infection. Thick fasciocutaneous flaps are useful for contour and shape reconstruction. Thin fasciocutaneous flaps provide stable, noncontracting coverage. Bone flaps provide structural integrity.

,

Specific aspects of each flap harvest are discussed elsewhere in this book. Certain principles, however, hold true despite the flap chosen. While harvesting a flap, the pedicle should be carefully dissected with as much length as possible. It is important not to limit the pedicle length to the anticipated need, but to harvest the maximum that can safely be obtained. It is much more advantageous to discard unneeded length than to find oneself requiring more pedicle length. Vein grafts should be avoided unless absolutely necessary.

While harvesting the flap and dissecting the pedicle, the most common mistake is damaging the vessels. Forceps should only touch the adventia and never purchase the vessel as the intimal layer is extremely fragile and easily fractured or crushed by manipulation. Any grasping of the vessels will cause damage to the intima which increases the likelihood of clot formation. This intimal injury leads to platelet deposition and thrombosis as the injured endothelial cell layer loses its natural thrombolytic properties.

Division of the pedicle should be reserved until the last possible moment. Prior to division, the donor vessels should be dissected, isolated, prepared and positioned for the anastomosis. It is helpful to mark the vessels in their natural state to assure that they are not twisted when transferred to the recipient site. Prior to division, the artery should be occluded first, followed by the vein. This will avoid excess blood pooling in the flap. Immediately after the flap is removed, one can consider cooling the flap with chilled saline as this decreases the metabolic activity of the tissue and allows the luxury of a longer ischemic time.

There is seldom a need to separate the artery and vein within the pedicle for anything more than a minimal distance. The only exception is the case where the recipient vessels are not paired. The vessels should not be skeletonized until they are brought to the recipient site and carefully prepared under the microscope. Any branches within 2 mm of the anastomosis are best sutured closed with microtechnique to avoid blood pooling near the anastomosis.

Preparation of Recipient Site

Preparing the recipient site mirrors the harvest of the flap. Vessels should be chosen that are simple to use and of the largest caliber available. They should be expendable when possible and have sufficient length. Again, care should be taken in the preparation of the vessels. They should not be extensively manipulated or injured. They should only be skeletonized for 2-3 mm around the anastomotic site, and this should be done under the microscope.

Microsurgical Technique

The anastomosis can be done in several fashions. These include end-to-end or end-to-side. They can be performed by multiple suture techniques or with coupling devices. The general philosophy is to gain experience with two or three techniques and apply those techniques to different situations. With careful planning, preparation, and mobilization of both the pedicle and recipient vessels, this is generally possible.

General principles of proper microsurgical technique are:

1. Pass sutures perpendicularly through the adventitia into the intima.
2. Avoid grasping or manipulating the intima.
3. Avoid multiple suture passes.
4. Avoid torquing the needle in the vessel; grasp and regrasp the needle in order to pass it through the vessel following the curve of the needle perfectly.
5. Dilate and visualize the inside of the vessels with heparinized saline irrigation on an ocular anterior chamber needle.
6. Use polished vessel dilating forceps to gently open spasmodic vessels or for vessel expansion.
7. Leave long tails on the sutures for manipulation and visualization.
8. Perform both anastomoses prior to reperfusion.
9. Release clamps on the vein first.
10. Inspect the anastomosis using the long suture tails as handles.
11. Place additional sutures in gaps with pulsatile or pressurized bleeding.
12. Avoid the temptation to place excess sutures in cases of mild oozing of blood from the anastomosis.
13. Apply warm saline to the flap and papaverine to the anastomosis after reperfusion to dilate the vessels and relax spasm.

Anastomotic Techniques

End-to-End

The end-to-end anastomosis is the simplest and the most reliable method. There are several techniques of suture placement including the 180˚-180˚ and triangulation methods. The easiest is probably the 180˚-180˚ technique. This can be applied to any situation and is probably the best technique for size-mismatched vessels.

Important points to remember are:

1. The vessels must not be twisted prior to placement in the double clamp holder. This can be ensured by inking one surface of the pedicle and recipient vessels prior to their division or dissection.
2. The first two sutures are placed at opposite poles of the vessels.
3. The third suture is placed midway between the poles.
4. In most cases, the next sutures bisect the gap though on occasion, two sutures will be needed in the gap.
5. Once the anterior wall is complete, twist the entire double clamp to show the backwall.
6. Visually inspect every suture of the anterior wall from the posterior view to assure that they are evenly spaced and have not purchased the back wall of the vessel.
7. Place another bisecting suture midway between the poles on the back wall.
8. All remaining sutures can be placed and left long (not tied).
9. Dilate the vessel with saline when tying the back wall to assure that there is no purchase of the anterior wall.

End-to-Side

The end-to-side technique is occasionally necessary. For example, it is used in the leg when there is only one vessel available or for an anastomosis in the head and neck (for example, to the internal jugular vein). Principles are:

1. The pedicle vessels should enter the recipient vessel at a gentle angle.
2. Perform a limited arterioectomy, removing a small window of vessel.
3. Place heel and toe sutures first.
4. Initially close the heel.
5. Follow with closure of the toe.

Coupling Devices

Coupling devices are useful for veins or thin-walled arteries. They save some time in the anastomosis. They, however, are not a panacea. The major time consumption in a microsurgical case is not the anastomosis, but the set up and preparation. If coupling devices are used, the set up and preparation time remain the same. Principles of gentle handling of vessels are still required as is avoidance of damage to the intima. Overall, the devices appear to have a place in the venous anastomosis, where they can also act as a stent, or in cases with significant size mismatch. Points to consider are:

1. Use the largest size coupler that will comfortably fit (range 2-3.5 mm).
2. Draping of the vessel over the spikes is performed by one surgeon while the other maintains the engagement of the spike as the vessel is seated.
3. Seat the vessel 180˚ apart to assure even spacing on the coupler.
4. Avoid grasping the intima of the vessel as it is draped over the spikes.
5. Assure that the coupling device is closed and guide it off of the coupling applier.

Draping of the Pedicle

After the anastomosis is complete and the flap is successfully revascularized, it is not uncommon for significant problems to arise. Kinking or unnatural curvature of the pedicle will certainly cause thrombosis. In fact, any turbulent, nonlaminar flow increases the likelihood of thrombosis and flap loss. The pedicle should be carefully draped. Gelfoam sponge or Alloderm can be used to help maintain the proper position of the pedicle.

Closure

A sound closure technique is again crucial for success. Both the flap and pedicle can be compressed by a tight closure. Anticipation of this is critical, as well planned incisions will allow closure after the edema of these long cases has set in. If there is any question, the liberal use of skin grafts to allow tensionless closure is recommended. The anastomosis should never be situated immediately under a suture line.

Monitoring

There is no “perfect” monitoring technique. Despite numerous ingenious techniques and improvements in technology, the ideal monitoring technique should be the one that surgeons and ancillary staff at a particular hospital are most familiar with and meet the restraints (budgetary or manpower) of the institution. What is ideal at one institution may not be practical at another. What is clear over many years of clinical experience, although this remains to be formally proven, is that the presence of dedicated staff in a dedicated unit stands the best chance of picking up problems earlier. The impetus to closely monitor a flap comes from the enormous investment undertaken on the part of the patient as well as the surgeon regarding microvascular free tissue transfer. The utility of postoperative flap surveillance has been proven, with an increase in the salvage rate of the failing flap from 33% to about 70% in some series.

The clinical exam is useful when performed by the experienced clinician. The transition of a healthy, plump flap or vibrant replanted digit to cold, flat, lifeless tissue can proceed via either arterial occlusion or venous congestion. These characteristics are useful in deciding whether to explore a flap or perhaps treat with leech therapy. Although it is the least technologically-based, much information can be gleaned from a thorough physical exam. Turgor can indicate the state of arterial inflow or venous outflow. Like a balloon, the flap or digit will inevitably declare itself if it has arterial insufficiency or venous congestion. Bleeding can be useful, as the qualitative and quantitative flow in response to pinpricks or rubbing of wound edges can declare the state of circulatory flow to the flap. In particular, a congested flap may bleed briskly, but the blood will appear dark and unoxygenated. The blood flow of a flap with compromised arterial inflow will be weak or absent. A caution regarding the pinprick test is that it is useful for evaluating a flap, but will occasionally cause trauma leading to vasospasm or hematoma in the confined space of a finger.

It is possible to monitor free flaps with a temperature probe. This method consists of placing surface temperature probes on the skin of the free flap and comparing them to probes placed on neighboring native skin. The probes are attached to a temperature monitor that will give off an alarm if there is a difference in temperature between the two sites greater than the specified amount (typically, 2-3˚C). Although appealing, there are limitations to the use of temperature probes, as the readings may be affected by regional changes in blood flow that are not secondary to flap flow disturbances.

Doppler ultrasonography is perhaps the most widely used monitoring tool. Two permutations exist. The first is the external Doppler. A recent innovation is the implantable internal Doppler. This tool permits monitoring of the segment of artery and vein a short distance downstream of the anastomosis. Its use has obviated the need for an external sentinel skin segment, and is ideally suited for buried anastomosis (e.g., jejunal free flaps in the head and neck, or vascularized bone transfers). These techniques are extremely useful; however, complications such as probe dislodgement and the occasional monitoring of an adjacent vessel that is not the pedicle can result.

In replants, the pulse oximeter is extremely useful. Some centers have reported success with fluorescein infusion and fluorescent lamp observation. This technique is not as useful in pigmented skin. Other techniques that at this time must be considered experimental include pH monitoring, duplex ultrasound, photoplethysmography, reflection photometry and radioisotope studies. None of these are currently widely used.

Pearls and Pitfalls

Although the microsurgical trainee may be eager to execute a large variety of occasionally exotic flaps, it is much more important to master a limited number of flaps and apply these flaps to different defects throughout the body. The principles outlined in this chapter serve as the basis to successfully execute any type of microsurgical transfer the plastic surgeon will encounter, even unusual flaps. In summary, it is essential to:

1. Sharpen microsurgical skills in the lab.
2. Handle the vessels gently.
3. Place significant attention on closure and pedicle position.
4. Familiarize oneself with one or two monitoring techniques. This will maximize salvage of the inevitable free flap failure.

The most important indicator of a problem with the free-flap is a change in the

clinical exam. This necessitates that the flap be seen as soon as possible by a surgeon who has been actively managing the patient.

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Principles of Surgical Flaps

Introduction

The underlying principle of all surgical flaps is the ability to maintain a viable blood supply upon transfer of flap tissue from a donor site to a recipient site. Given this fundamental capacity to retain vascular circulation, surgical flaps may be classified in many ways. One approach is by composition, as a flap may be made up of many different kinds of tissue. Another is by vascularity, and several different schemata have been developed to categorize flaps by the type of vascular supply. A third manner of categorizing flaps is by method of movement, and it is important to understand the basic techniques of flap transfer. Unlike a graft, which is wholly dependent upon the recipient bed to provide blood supply, a flap by definition is able to preserve its own vascular supply for survival. Thus, whether classifying a flap by composition, vascularity or method of movement, the core principle essential to all flaps is how to maintain blood supply so that the flap tissue will remain robust after transfer to its new site.

Composition

The most basic way to think about a flap is to consider what tissues are contained within it. A flap may contain skin, fascia, muscle, bone or various combinations of these tissues. As the underlying principle of any flap is its ability to retain its own blood supply, the amount of tissue that may be carried within it is dictated by the minimum or maximum amount of tissue that can be transferred with intact vascularity. When more than one type of tissue is contained within a flap, it is called a “composite flap.”

The simplest type of flap is the skin flap. The blood supply of the skin is contained largely in the dermal and subdermal plexus and derives from two main sources: a musculocutaneous vascular system and a direct cutaneous vascular system. When the blood supply to the skin is via a named artery, the skin flap is called an “axial flap.” When the blood supply to the skin lacks a significant pattern in its vascular design, the skin flap is called a “random flap.” Either way, the survival of a cutaneous flap depends on the number and type of blood vessels at the base of the flap. For an axial flap, the survival pattern of the flap is based on the length of the underlying feeding artery. For a random pattern flap, the length and width should be designed in a 2:1 ratio, as a wider base width increases the chance that a large vessel will be incorporated to provide an adequate blood supply to the enclosed dermal-subdermal plexus. Even in an axial flap, the distal borders of the flap are also random pattern with distal perfusion from the dermal-subdermal plexus .

Skin flaps may also be transferred based on the vascular plexus of the deep fascia, in which case they are termed “fasciocutaneous flaps.” The blood supply of the deep fascia is derived from perforating vessels of regional arteries that pass along the fibrous septa of muscle bellies or muscle compartments. Including the deep fascia along with the skin avoids tedious dissection and may also preserve adjacent subfascial arteries. Among the advantages of fasciocutaneous flaps in reconstructive surgery are ease of elevation and transfer, decreased bulk, good reliability, and decreased functional morbidity at the donor site. Depending on the size of the skin paddle, however, the secondary defect at the donor site may require coverage with a split-thickness skin graft.

Progressing one layer deeper still, another common flap in reconstructive surgery is the “myocutaneous” or “musculocutaneous” flap, which combines muscle, skin, and the intervening fascia and subcutaneous tissue. Supplied by one or more dominant vascular pedicle within the muscle instead of a direct cutaneous arterial source, the essential feature of a myocutaneous flap is that the underlying muscle “carries” the blood supply for the overlying skin. Myocutaneous flaps have two key advantages. First, the increased bulk better allows it to fill dead space. Secondly, myocutaneous flaps are also more resistant to bacterial infection than fasciocutaneous flaps by a factor of 100. This makes them very reliable and useful, particularly when increased bulk is needed with a robust arterial supply to fill a defect that has been subjected to chronic infection. If a skin paddle is not needed, muscle can also be transferred alone, without the overlying fascial and cutaneous tissue.

A final type of tissue commonly incorporated into a flap is bone. When taken with the overlying skin, this is called an “osseocutaneous flap.” A dominant vascular pedicle with perforating branches supplies the skin and periosteum. Usually taken as a free flap, the bone is harvested with a cuff of muscle and/or skin to reconstruct a skeletal framework with soft tissue. The long bones of the extremities, such as the fibula, are often used as they provide more length for shaping according to the required need.

Type of Blood Supply

Once the composition has been determined, flaps can be further categorized according to their blood supply. As mentioned earlier, random flaps are based primarily on the cutaneous blood supply from the dermal-subdermal plexus. Pedicled or axial flaps are based on anatomically mapped or named blood vessels.

Fasciocutaneous flaps have been classified into three categories based on their vascular patterns.

Type A: Direct cutaneous pedicle

Type B: Septocutaneous pedicle

Type C: Musculocutaneous pedicle Muscle flaps may be classified in two different ways. First, Mathes and Nahai developed a system of muscle classification based on circulatory patterns.

Type I: Single pedicle (e.g., tensor fascia lata)

Type II: Dominant pedicle(s) with minor pedicle(s) (e.g., gracilis)

Type III: Dual dominant pedicles (e.g., gluteus maximus)

Type IV: Segmental pedicle(s) (e.g., sartorius)

Type V: Dominant pedicle, with secondary segmental pedicle(s) (e.g., latissi

mus dorsi) Second, Taylor developed a system of muscle classification based on mode of innervation.

Type I: Single, unbranched nerve enters muscle (e.g., latissimus dorsi)

Type II: Single nerve, branches prior to entering muscle (e.g., vastus lateralis)

Type III: Multiple branches from the same nerve trunk (e.g., sartorius)

Type IV: Multiple branches from different nerve trunks (e.g., rectus abdominis)

Finally, the body can be further segregated anatomically into three-dimensional vascular territories called “angiosomes.” The angiosome is a composite unit of skin and underlying deep tissue that is supplied by a source artery. Each angiosome defines an anatomic unit of tissue from skin to bone that may be safely transferred as a composite flap. The angiosomes are interconnected by either true anastomotic arteries, in which there is no change in caliber between the vessels of adjacent angiosomes, or reduced-caliber, choke anastomotic vessels. The junctional zone between adjacent angiosomes usually occurs within the muscles of the deep tissues rather than between them, so that most muscles span across two or more angiosomes. Thus, when designing musculocutaneous flaps it is possible to capture the skin island from one angiosome by using muscle supplied from the adjacent angiosome.

Flap delay is defined as the surgical interruption of a portion of the blood supply in a preliminary stage prior to tissue transfer. The purpose of delay is to augment the surviving portion of the flap. There are two schools of thought regarding the pathophysiology of the delay phenomenon. The first holds that delay conditions tissue to ischemic conditions so that it is able to survive with less vascular inflow. The second believes that delay actually increases vascularity by dilating reduced-caliber choke anastomotic vessels and stimulating additional vascular ingrowth.

Another way to increase survival of a myocutaneous flap is by supercharging the blood supply. This method involves augmenting arterial inflow by using microsurgical techniques to bring in an additional vascular pedicle. Classically described for use in a pedicled TRAM flap, the supercharging technique may be performed in one of two ways. First, in the pedicled TRAM flap, the contralateral deep inferior epigastric vessels may be retained in a cuff of inferior rectus muscle in a planned vascular augmentation to a single-pedicle flap. Alternatively, the inferior epigastric vessels on the pedicled side may be used to save a flap during the immediate postoperative period in an emergency “supercharged” TRAM flap.

Techniques of Flap Transfer

The final way to categorize flaps is by the technique of flap transfer. Broadly speaking, flaps can either be pedicled flaps or free flaps. Pedicled flaps remain attached to the underlying blood supply, while the tissue connected to it is transferred to another site. Free flaps are temporarily disconnected from their blood supply, and then the feeding vessels are surgically anastomosed to the blood supply at the recipient site. Flaps can be further categorized by the distance between the donor site and recipient site. Local flapsare used to close defects adjacent to the donor site. Distant flaps imply that the donor site and the recipient site are not in close proximity so that closure cannot be facilitated by a local method.

There are several different types of local flaps. An advancement flap moves along an axis in the same direction as the base to close the defect simply by stretching the skin. Examples of an advancement flap are the V-Y flap, Y-V flap, and the bipedicled flap (. A rotation flap has a curvilinear design and rotates about a pivot point to close a wound defect. The donor site is closed primarily by reapproximating the skin edges or with a skin graft. A back cut in the direction of the pivot point can be made to facilitate closure, but this can also compromise the blood supply to the flap by decreasing the base width. A Burow’s triangle can also be made external to the incision to decrease tension and facilitate primary closure of the donor site . Finally, atransposition flap is a rectangular flap that is rotated laterally about a pivot point into an adjacent defect to be closed. The farther the flap rotates, the shorter the effective length of the flap, so that the flap must be designed longer than the defect in order to close the donor site. Otherwise, the donor site may be closed primarily with a skin graft or with an additional transposition flap, as in a bilobed flap .

There are several important types of transposition flaps. The first is the Z-plasty, in which adjacent triangular flaps are interchanged to exchange the width and length between them. The three limbs of the Z must be equal in length, and the amount of length obtained depends upon the intervening angles, with 60˚ being the classic angle to obtain optimal increase in length while preserving blood supply to the triangular flaps . The rhomboid or Limberg flap is another type of transposition flap that can be used to close a skin defect. Four different flaps can be designed at angles of 60˚, with the longitudinal axis paralleling the line of minimal skin tension . The Dufourmentel flap is like the rhomboid flap, except the angles are at 90˚. Finally, the double opposing semicircular flap can be used to close circular skin defects .

Interpolation flaps also rotate about a pivot point, but they are either tunneled under or passed over intervening tissue to close a defect that is not immediately adjacent to the donor site. Examples include the Littler neurovascular island flap and the pedicled TRAM flap.

Distant flaps involve tissue transfer from one part of the body to another in which the donor site and the recipient site are not in close proximity to each other. There are three types of distant flaps: direct flaps, tubed flaps and free flaps. The direct flap involves the direct transfer of tissue from a donor site to a distant recipient site. Examples of direct flaps include the thenar flap, cross-leg flap and groin flap. Tubed flaps are used when tissue cannot be directly approximated, so that tissue from the donor site is tubed to recipient site. Once the vascular supply has been established, the tube is divided and tissue from the tube is returned to donor site. Examples of this are the forehead flap and the clavicular tubed flap. Finally, free flaps involve complete disconnection of the underlying blood supply, so that the blood vessels from transferred tissue must be surgically reanastomosed to reestablish vascular circulation.

Summary

In sum, the underlying principle of all surgical flaps is the meticulous preservation of blood supply. Unlike grafts, a flap carries its own vascular circulation with it.

The amount and type of tissue that a flap can contain is wholly dependent on the maintenance of adequate blood supply. Knowledge of vascular anatomy is crucial to flap design. Techniques of flap transfer must take care to safeguard the vascular circulation of the flap. With the careful protection of blood supply, it is possible to successfully plan and implement any surgical flap.

Pearls and Pitfalls

The success or failure of a flap is dependent upon blood supply. The ingrowth of new blood vessels from the surrounding tissue occurs over several weeks. As a general rule, the tissue that is most distant from the arterial inflow is at the highest risk of necrosis. Efforts to reduce this risk include the following: (1) preferentially discarding excess tissue from the distant tip; (2) for skin flaps, designing a flap with as broad a base as possible, away from any previous incisions sites; (3) minimizing tension; (4) maximizing inflow.

When designing a flap for covering or filling a defect, it is prudent to follow the carpenter’s rule of “measure twice, cut once.” Defects must be examined and measured three-dimensionally, since the width, depth and length will not always conform to a two-dimensional plane. The final desired contour should also be considered (e.g., if a convex contour is desired, the length of the flap should be greater than the direct length of the defect). Furthermore, it should be determined whether or not moving adjacent structures (such as the arms or legs) will change the dimensions of the defect. For instance, a supraclavicular skin defect will significantly increase in size when the patient’s head is turned away from the defect.

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