Principles of Microsurgery Technique

Because of the complexity of microsurgical procedures, adhering to guidelines such as the following can be helpful in achieving a high success rate:

• The patient must be able to tolerate a surgery that lasts 8 hours or longer
• The flap should be planned in accordance with the size and type of tissue needed, and an alternative flap should be considered as a "lifeboat"
• The recipient vessel should be planned outside the zone of injury
• The patient and the family must understand the full extent of the procedure, as well as all risks and possible complications, including the possible devastating complication of flap loss
• The surgical plan should be discussed with the operating team, including the anesthesiologists and the circulating and scrub nurses; this discussion should include the length of the procedure, the positioning of the patient and any need to change position, and the indications and contraindications for the use of specific pharmacologic agents
• The plan should also be outlined to the circulating nurses and scrub nurses; if two surgical teams are to operate simultaneously, care must be taken to ensure that adequate nurses are available

The use of multiple simultaneous free flaps may be an option for head and neck reconstruction in selected patients with defects that involve several tissue types, multiple functional areas, or large volumes. ^[23]

After the decision has been made to proceed with a microsurgical reconstruction, the optimal flap must be chosen. This decision is based on the following factors:

• Size of the defect
• Type(s) of tissue required for the repair (bone, muscle, fascia, tendon, nerve, skin)
• Length of the vascular pedicle
• Reliability of the flap

Perforator flaps involve the dissection of terminal blood vessels into a tissue segment. These flaps not only have gained significant popularity in recent years as a result of a better understanding of the anatomy and blood supply to specific tissue territories but also have revolutionized the field of microsurgery. By dissecting the blood vessels to the flap and sparing the surrounding tissue, large flaps can be harvested with minimal functional loss to the patient. The following three perforator flaps are described in this article:

• Anterior lateral thigh (ALT) flap
• Superior gluteal artery perforator (SGAP) flap
• Deep inferior epigastric artery perforator (DIEP) flap ^[24]

The following is a list of common, reliable flaps that are used in reconstructive surgery.

Anterior lateral thigh flap

The ALT flap is a fasciocutaneous flap that is located over the middle third of the thigh anterior and lateral to the rectus femoris and the vastus lateralis. Although the flap is supplied by musculocutaneous perforators 85% of the time, it can be raised as a perforator flap, with minimal disruption of the underlying musculature. It is usually used for coverage of defects when a relatively thin flap is required, but it can be harvested with parts of the vastus lateralis muscle when a flap with more volume is required.

Characteristics are as follows:

• Type - Fasciocutaneous
• Dominant pedicle - Septocutaneous branches of the descending branch of the lateral circumflex femoral artery and venae comitantes
• Innervation - Sensory, derived from the lateral femoral cutaneous nerve (L2-3)

Radial forearm flap

This is a useful and versatile flap with a long vascular pedicle and thin, pliable skin that was widely used in China before becoming popular in the Western literature. It is based on the radial artery and can achieve a pedicle length of 20 cm and a diameter of 2.5 mm. The flap size can reach an area of 10 × 40 cm². ^[25]

Raising this flap sacrifices a major artery to the hand; therefore, before harvesting this flap, check that the perfusion to the hand is preserved through the ulnar vascular system. The osteocutaneous flap raises the risk of radius fracture if not carefully harvested. In addition, exposure of the flexor tendons must be avoided by careful preservation of the paratenon and coverage of tendons with surrounding muscle bellies prior to skin grafting.

Characteristics are as follows:

• Type - Fasciocutaneous or osteocutaneous
• Dominant pedicle - Radial artery, venae comitantes, and cephalic vein
• Innervation - Medial and lateral antebrachial cutaneous nerves (sensory)

Lateral arm flap

This flap can be harvested as a fasciocutaneous, innervated fasciocutaneous, or deepithelialized subcutaneous fascial flap. It is supplied by the posterior radial collateral vessels. It does not sacrifice a major vessel in the arm and may be harvested in the same upper extremity that requires reconstruction.

The flap may be bulky, and the pedicle may be short (up to 7 cm). The posterior brachial cutaneous nerve (C5-6) innervates the flap when it is harvested as a sensate flap. The donor site may be closed, if laxity is present in the upper arm, or skin grafted. In either case, the donor scar may be conspicuous.

Characteristics are as follows:

• Type - Fascial or fasciocutaneous
• Dominant pedicle - Posterior radial collateral artery and venae comitantes (branch of profunda brachii artery)
• Innervation - Posterior cutaneous nerve of the arm (sensory); additional sensory from the posterior antebrachial cutaneous nerve

Scapular flap

The pedicle for this flap is long and reliable. It is a thin, sometimes hairless, skin flap from the upper back and can be deepithelized and used as a subcutaneous fascial flap, pedicled flap, or free flap. However, the scapular flap has the following drawbacks:

• The patient must be positioned in either the lateral decubitus position or the prone position for harvest
• The sensory innervation is not reliable
• The skin may be too bulky, depending on the body habitus of the patient

Characteristics are as follows:

• Type - Fascial, fasciocutaneous, or osteocutaneous
• Dominant pedicle - Circumflex scapular artery and vein
• Innervation - Lateral and posterior cutaneous nerves of third to fifth intercostal nerves (sensory)

Groin flap

The groin flap can provide a large skin and subcutaneous tissue territory based on the superficial circumflex iliac artery and vein. It is particularly helpful when thin tissue coverage is required. The flap can be as large as 10 × 25 cm². A tissue expander can be placed under the deep groin fascia, which can expand the flap and allow direct donor-site closure. The small diameter of the superficial circumflex iliac artery and the variable vascular anatomy make this flap less popular than other free tissue transfers.

Characteristics are as follows:

• Type - Fasciocutaneous
• Dominant pedicle - Superficial circumflex iliac artery and venae comitantes and superficial circumflex iliac vein

Superior gluteal perforator flap

The SGAP flap is a perforator flap used mainly for breast reconstruction. The abdomen is the most common harvest site for autologous breast reconstruction; however, in some cases (eg, patients who have excessive scarring or are very thin), the abdomen is not an option as a donor site. The gluteal region and the SGAP flap offer alternatives when the abdomen is unavailable as a donor site.

Characteristics are as follows:

• Type - Fasciocutaneous
• Dominant pedicle - Superior gluteal artery perforators

Latissimus dorsi flap

This flap is a very reliable flap with large muscle mass that can be harvested with or without a skin paddle. The primary vascular pedicle can be as long as 8 cm. If additional tissue is needed, the latissimus dorsi muscle may be raised with the serratus anterior muscle, a scapular flap, or both on a single pedicle. One drawback is the need for positioning the patient in a lateral decubitus position for harvests.

Characteristics are as follows:

• Type - Muscle or musculocutaneous
• Dominant pedicle - Thoracodorsal artery and vein
• Minor pedicle - Perforators from the posterior intercostal arteries and lumbar artery and venae comitantes
• Innervation - Thoracodorsal nerve (motor)

Rectus abdominis flap

This is a reliable flap with a large muscle mass and skin paddle. The vertically oriented muscle extends between the costal margin and the pubic region and is enclosed by the anterior and posterior rectus sheaths. It has two dominant pedicles, one based on the superior epigastric artery and vein and the other based on the inferior epigastric artery and vein.

The pedicle is large and reliable. The flap may be harvested with the patient in a supine position. One drawback to this flap is the possibility of abdominal hernia after sacrifice of one of the rectus abdominis muscles. Careful closure of the layers of the abdominal wall is critical to prevent this occurrence. Currently, the DIEP flap is becoming increasingly popular as a donor site for breast reconstruction. Its main advantage is the decreased morbidity to the abdominal wall.

Characteristics are as follows:

• Types - Muscle or musculocutaneous (transverse rectus abdominis myocutaneous [TRAM], vertical rectus abdominis myocutaneous [VRAM], muscle-sparing TRAM)
• Dominant pedicles - Deep inferior and superior epigastric arteries and veins
• Innervation - Seventh to 12th intercostal nerves (motor) and lateral cutaneous nerves from the seventh to 12th intercostal nerves (sensory)

Superficial inferior epigastric artery flap

The superficial inferior epigastric artery (SIEA) flap has become more popular for breast reconstruction, but the presence of superficial epigastric blood vessels that nourish the flap is variable. Although there are advocates of preoperative imaging studies, the true presence of these vessels can only be determined intraoperatively. If they are not found, the surgeon must be prepared to harvest an alternate flap, which in breast reconstruction is more commonly the DIEP flap. Usually, only a hemiabdomen is perfused with the SIEA flap.

Characteristics are as follows:

• Types - Muscle or musculocutaneous
• Dominant pedicle - Superior epigastric artery and veins
• Innervation - Seventh to 12th intercostal nerves (motor) and lateral cutaneous nerves from the seventh to 12th intercostal nerves (sensory)

Gracilis flap

The gracilis is a thin and flat muscle that lies between the adductor longus and the sartorius anteriorly and the semimembranosus posteriorly. It has a dominant pedicle and several minor pedicles. The dominant pedicle is the ascending branch of the medial circumflex femoral artery and the venae comitantes. This flap is useful for reanimation of facial paralysis or for extremity muscle function. The vascular pedicle is usually short, and the vessels are small. The skin paddle is typically unreliable.

Characteristics are as follows:

• Types - Muscle or musculocutaneous
• Dominant pedicle - Ascending branch of the medial circumflex femoral artery and vein
• Innervation - Anterior branch of the obturator nerve (motor) and anterior femoral cutaneous nerve (sensory)

Tensor fasciae latae flap

The tensor fasciae latae (TFL) flap has one dominant vascular pedicle, which is the ascending branch of the lateral circumflex femoral artery from the profunda femoris and venae comitantes. The muscle may be as large as 15 × 5 cm², and the skin flap can achieve a size of 7-9 × 22-26 cm².

Characteristics are as follows:

• Type - Muscle, musculocutaneous, musculofascial, or musculofasciocutaneous
• Dominant pedicle - Ascending branch of the lateral circumflex femoral artery

Omental flap

The omental flap allows for a large volume of pliable tissue; however, harvest requires a laparotomy. The omentum flap is ideal for obliteration of irregular dead space cavities or for provision of thin coverage over an exposed tissue such as bone.

The omentum is considered a visceral structure containing fat and blood vessels within a thin membrane. It extends from the stomach to beyond the transverse colon and covers the anterior aspect of the peritoneal contents. It has two dominant pedicles: (1) right gastroepiploic artery and vein and (2) left gastroepiploic artery and vein. Previous intra-abdominal surgery, which can create extensive omental inflammatory adhesions, may preclude the use of an omental flap.

Characteristics are as follows:

• Type - Vascularized fat
• Dominant pedicle - Right or left gastroepiploic artery and vein

Jejunal flap

The jejunal flap is reserved for pharyngeal or esophageal reconstruction. The intestinal mucosa does not tolerate ischemia; therefore, revascularization must proceed immediately. Postoperative monitoring may be performed with a sentinel loop of intestine that is exteriorized.

Characteristics are as follows:

• Types - Vascularized intestine
• Dominant pedicle - Jejunal artery and accompanying vein

Fibula flap

This flap offers a large segment of bone that may be recontoured by osteotomies with or without a skin paddle. In patients with abnormal distal extremity pulses, angiography or magnetic resonance angiography (MRA) of the lower extremity is indicated. The skin paddle is reliable when care is taken to preserve the fasciocutaneous perforators.

Characteristics are as follows:

• Type - Osseous long bone or osteocutaneous
• Dominant pedicle - Peroneal artery and vein
• Innervation - Superficial peroneal nerve (sensory)

Temporoparietal fascia flap

The temporoparietal fascia (TPF) flap is a versatile thin flap with many applications and consistent vascular anatomy with a pedicle of small caliber. It provides a thin sheet of vascularized fascia based on the superficial temporal artery and vein. The temporal muscle fascia lies deep to the TPF over the temporalis muscle. The pedicle length is short, up to 3 cm in length.

Characteristics are as follows:

• Type - Fasciocutaneous
• Dominant pedicle - Posterior branches from the superficial temporal artery and venae.
• Innervation - Not harvested as a sensory flap

Great toe flap

The great toe flap can be used to reconstruct part of the thumb (see the image below) or as a neurosensory flap. This flap allows composite tissue reconstruction for loss of the thumb without significant loss of function to the foot. However, some patients may not wish to sacrifice a great toe for aesthetic reasons.

Characteristics are as follows:

• Type - Composite (bone, tendon, nerve, skin, nail) or fasciocutaneous
• Dominant pedicle - First dorsal metatarsal artery and vein
• Minor pedicle - First plantar metatarsal artery and vein
• Innervation - Digital nerves (sensory), dorsal cutaneous nerves from the superficial peroneal nerve, deep peroneal nerve

Surgery always begins with resection of the tumor or the diseased area and proper exploration and preparation of the recipient site. Control of infection and adequate debridement are necessary prior to flap transfer.

The need for free flap reconstruction should be reevaluated intraoperatively. In some instances, reconstruction may be performed by using skin grafts or local flaps, according to the reconstructive ladder. ^[26]

Doppler ultrasonography (US) is useful for localizing recipient vessels. ^[27]  The recipient artery and vein must be critically evaluated, and the surgeon must be satisfied with inflow and outflow before embarking on flap harvest. A common pitfall is remaining within the zone of injury on a traumatized or irradiated vessel for microanastomosis, which results in higher rates of vessel thrombosis.

The dimensions and tissue needs of the defect are determined, and the choice of flap is made. An important issue is the orientation and the length of the vascular pedicle. The surgeon must measure the length of pedicle needed to reach the recipient vessels and compare that with the pedicle length available.

Performance of microsurgical anastomoses requires meticulous technique and adherence to the following principles:

• The recipient vessels and the match between the size of the recipient and pedicle vessels must be carefully assessed
• Preparation of vessels to healthy untraumatized tissue (ie, their pretraumatized state), removal of intravascular clots and debris, and irrigation with heparinized saline (100 U/mL)
• Vessel side branches are examined and legated to prevent hematoma
• Either end-to-end or end-to-side anastomoses may be performed, depending on the recipient vessel, the orientation of the flap, and the match between the size of the vessels
• Avoidance of vessel tension, kinking, and twisting is important
• If tension is excessive, vein grafting is preferred
• Simple interrupted full-thickness sutures are preferred and the standard to which all new anastomotic techniques are compared
• Once flow is established, the anastomotic sites are bathed with warm irrigation and papaverine to relieve vasospasm
• Vascular anastomoses are finally examined, and the vascular strip test is performed to check flow; this test is performed by gently occluding the vessel distal to the anastomosis with a microforceps and "stripping" the vessel with another microforceps proximally across the anastomosis; brisk blood flow should then be observed to return across the anastomosis when the proximal microforceps are released

The vein coupler is increasingly popular and is a useful tool for anastomosing the vein. In the right hands, the coupler is efficient and can help decrease the total operative time.

Final inset of the flap is performed with care to prevent compression of the vascular anastomoses. Occasionally (eg, in head and neck cases), the inset of the flap is done before the anastomosis.

While the patient is under anesthesia, final assessment of flap viability is made by clinical observation, and vascular flow is confirmed with Doppler examination. The location of Doppler signal in the flap is marked with a stitch for postoperative monitoring. Internal Doppler probes are used when the flap is completely buried under the skin.

Loose dressings are applied, with a portion of the flap exposed for postoperative monitoring. Splints, if needed, should also be free of compression. Particular attention should be given to the position of the patient to avoid compression or pulling on the pedicle.

The postoperative ward must be staffed with nurses who are familiar with free flap monitoring and general care for patients who have undergone microsurgery.

Pain is well controlled to prevent pain and anxiety leading to vasoconstriction. Adequate fluid hydration and body temperature are maintained. The location of the free flap is elevated to promote venous drainage and minimize swelling.

Anticoagulation may be used, depending on the operation and surgeon preference. Possible anticoagulant choices include the following:

• Dextran 40
• Heparin
• Lovenox
• Aspirin

Free flap monitoring depends on the operation and surgeon preference. The criterion standard for monitoring remains careful clinical examination with an eye to skin color, capillary refill, and flap turgor. Pricking the flap with a needle should result in bright-red blood. ^[28]  Currently, there is no consensus on which method is most effective for monitoring of free flaps, but handheld Doppler US and physical examination remain the standard of care in most institutions. Methods of monitoring the flap include the following:

• Surface Doppler US
• Temperature monitoring
• Implantable Doppler US
• Pulse oximetry
• Intravenous fluorescein

Vascular compromise includes congestion or ischemia of the flap, and it may develop very quickly or more slowly. When a vascular compromise occurs suddenly, the patient must be taken immediately to the operating room for exploration of the anastomotic site. When the signs of vascular compromise occur more gradually, the following measures should be immediately undertaken:

• Reposition the patient to relieve possible vascular pedicle compression
• Remove compressive dressings
• Release tight sutures
• Assess hydration

If these simple maneuvers at the bedside are not successful, immediate reexploration in the operating room is critical.

Postoperative complications include the following:

• Flap compromise due to vein or artery thrombosis
• Flap congestion
• Fat necrosis
• Hematoma with pedicle compromise and need for transfusion
• Infection
• Wound breakdown
• Wound complication associated with the donor site
• Systemic complications associated with anesthesia
• Deep vein thrombosis and  pulmonary emboli