Overview

Despite the availability of numerous microvascular tissue flaps, only a few are routinely used in the head and neck including the radial forearm, fibula, rectus, scapula, latissimus, jejunum, iliac crest, and gracilis. The radial forearm or so-called 'Chinese' flap was first described by Yang et al. in 1981 (43). It provides thin pliable fasciocu-taneous tissue from the ventral wrist and forearm based on the radial artery, cephalic vein, and medial and lateral antebrachial cutaneous nerves. The proximal fibrofatty tissue in the forearm can also be harvested for augmentation or coverage in selected cases. The radial forearm flap can also be harvested with a portion of the underlying |

radial bone. However, pathological fracture of the radial bone is a significant risk »

despite prolonged cast immobilization. Considering the variety of alternative donor sites for vascularized bone, radial bone harvest is rarely warranted.

The fibula, scapula, and iliac crest are used nearly exclusively for bony defects in the head and neck. The fibular osteocutaneous free flap was originally described for use in mandibular reconstruction by Hidalgo et al. in 1989 (44). The fibula is a o tubular, primarily cortical, bone and is the longest available microvascular bone for mandibular reconstruction (26 cm). Since the bone is perfectly straight, several @

osteotomies are usually required, especially if it is being used to replace the mandibular symphysis. The blood supply to the bone is based on the peroneal artery and vena comitantes. Septocutaneous vascular twigs from the peroneal artery course posterior to the fibular bone and enter the posterior crural intermuscular septum to nourish the skin of the lateral leg. A skin paddle can be harvested with the fibular bone up to 6 cm wide along the entire length of harvested bone. Wider skin paddles leave a donor site that must be reconstructed with a skin graft. Sensory reinnervation is possible if the lateral sural cutaneous nerve is harvested with the skin paddle (45). Donor site morbidity is minimal and full unassisted ambulation is expected within 23 weeks postoperatively.

The scapular osteocutaneous flap was originally described by Swartz et al. in 1986 for mandibular reconstruction (46). The lateral border of the scapula provides approximately 16 cm of straight elliptical bone based on the circumflex scapula artery and vena comitantes. Large independent skin paddles can be harvested (transverse and parascapular fasciocutaneous flaps) with or without the underlying bone. The angular artery, a branch of the artery to the serratus muscle, additionally nourishes the distal third of the scapular bone. This artery should be preserved if a distal osteotomy is planned. Although the osteocutaneous scapular flap and the latissimus-serratus flaps can be harvested together based on the subscapular artery, this large flap is rarely needed. The donor site is rarely troublesome.

Taylor described the iliac crest osteocutaneous flap in 1982 for mandibular reconstruction (47). The iliac crest provides vascularized bone up to 16 cm in length that is naturally curved, lessening the need for osteotomies. The bone and overlying skin are based on the deep circumflex iliac artery. The overlying skin receives nourishment from septocutaneous branches, similarly to the osteocutaneous fibular flap. The bone height and cortical:cancellous ratio closely match the native mandible. The skin component of the iliac crest flap is excessively thick when it is used to cover the free edge of the bone intraorally, which is similar to the problems encountered with the skin components of the scapula and fibula flaps. Thick tissue over the neoalveo-lus impedes the placement of osseointegrated implants and implant-borne dentures. To avoid this problem, it is possible to harvest a portion of the thin internal oblique muscle with the iliac crest bone and skin based on the ascending branch of the deep circumflex iliac artery. The muscle can be draped over the neoalveolus and allowed to re-epithelialize providing improved contour to the neoalveolus that more closely matches the natural alveolus. Although the iliac crest flap is an excellent substitute for native mandible, there is significant donor site morbidity, which is the main drawback to using this flap. Chronic pain and difficulty walking are common, at least for the first several months postoperatively. There is also a risk of hernia and bowel injury. The significant morbidity associated with flap harvest has consid- -g erably lessened the initial enthusiasm for its use.

Tansini first described the latissimus musculocutaneous flap as a pedicled flap for breast reconstruction in 1896; Maxwell et al. subsequently described it as a free c flap in 1978 (15). The flap is supplied by the thoracodorsal artery and vein and the thoracodorsal motor nerve. The full muscle and overlying skin are more often indicated for extensive traumatic or oncological trunk or extremity wounds. The thora-codorsal nerve may be harvested with a portion of the muscle to maintain bulk and achieve movement. Donor site morbidity is usually minimal; however, the site is prone to delayed healing and seroma formation.

The rectus abdominis musculocutaneous free flap was first described in 1980 for an infraclavicular defect and in 1984 for use in the head and neck (48,49). The flap is based on the deep inferior epigastric artery and vein. The cutaneous component can be bulky with a substantial amount of subcutaneous fat that varies at the recipient site based on the patient's adiposity. Despite the size of the skin paddle, it can be sustained by a single periumbilical vascular perforator. Therefore, this so-called 'perforator flap' can be transferred with almost no underlying muscle except a muscular cuff around the lone vascular perforator. The motor supply is segmental, with short nerve twigs entering the lateral aspect of each rectus muscle. The multiple tendinous inscriptions limit muscle excursion, making it ineffective for facial reanimation. Donor site morbidity is minimal; however, hernia can occur especially if the anterior rectus sheath is not preserved below the arcuate line.

Seidenberg et al. first used the jejunal flap clinically to reconstruct a cervical esophageal defect in 1959. The flap fared well but the patient died of a stroke on postoperative day 5. The jejunal flap consists of a segment of jejunum 3 feet beyond the ligament of Treitz. The vascular supply is based on the mesenteric arterial arcade from the superior mesenteric artery and vein. The jejunal flap may be left intact and used as a conduit or split along its antimesenteric border and used as a patch. The revascularized jejunum actively secretes mucous and this attribute has been espoused for irradiated recipient sites.

Harii et al. introduced the gracilis free flap in 1976 for the surgical treatment of facial paralysis (50). It provides a tubular muscle innervated by multiple neural fascicles from the anterior division of the obturator nerve. The blood supply is from the medial femoral circumflex artery (a branch of the profunda femoris artery). The gra-cilis muscle, as is the case with all microvascular flaps for facial paralysis, is reserved for patients with absent or nonviable facial musculature. The obturator nerve is anastomosed to a motor nerve in the recipient site, most commonly the hypoglossal nerve or a previously placed cross-facial nerve graft. Cross-facial nerve grafting must precede microvascular flap transfer by several months to allow time for the regenerating axons to reach the recipient site. Although donor site morbidity is negligible regarding the gracilis muscle, sural nerve harvest leaves the patient with permanent numbness and paresthesia over the lateral foot. The diameters of the artery (1-2 mm) and the vein (1-1.5 mm) to the gracilis muscle are relatively small, making the micro-vascular anastomosis more difficult. A potential complication of flap harvest is paralysis of the adductor muscles of the extremity if the obturator nerve is taken too proximally but this is extremely rare. The latissimus muscle-thoracodorsal nerve flap may obviate the need for two stages by providing a sufficient length of nerve to reach the opposite donor facial nerve without the need for an intervening avascular nerve graft. Early experience with this technique appears promising, with good -g return of function within 8 months. |

Microvascular Technique I1

Microsurgery describes a surgical procedure performed under the magnification of a ^

d surgical microscope. Although the vast majority of vessel anastomoses involving free >3

tissue transfer are performed with the aid of a microscope (6-25x), surgical loupe |

magnification (2.5-3.5x) may be adequate for larger vessels with diameters over o 2.0 mm. The microscope should be configured with dual heads with stereovision to allow an assistant to be seated across the operating table (Fig. 22). Thorough ^

Figure 22 Surgically draped dual-headed microscope for microsurgery. The operator's oculars (A) are oriented 180° from the assistant's oculars (B).

attention to detail and meticulous atraumatic technique are essential components of success in microvascular surgery. Appropriate microvascular instrumentation is essential including straight jewelers forceps, a straight or curved microneedle holder, straight and curved microscissors, a vessel dilator, a clamp applicator, and a microbipolar (Fig. 23). An assortment of microvascular clamps should be available with closing pressures less than 30 g/mm2. The clinical instruments should be duplicated in a small animal laboratory to facilitate realistic training sessions. The novice microvascular surgeon should first practice microsurgical techniques using synthetic vascular material with diameters between 1 and 2.5 mm. After the basic skills are established, the surgeon should advance to the deep inferior epigastric artery and vein in the rat. Consistent performance resulting in serial patent anastomoses indicates sufficient expertise to proceed into the operating room. The number of laboratory training sessions needed varies but approximates 40.

It makes little difference whether the artery or vein is anastomosed first unless -g an impediment is created that will present problems with access to the subsequent anastomosis. End-to-end anastomoses are always done on the arterial side but »

end-to-side anastomoses are often performed on the venous side between the donor vein and the internal jugular vein. It makes no difference at what angle the donor d vein connects to the recipient vein unless the vein is kinked or compressed. The novice microvascular surgeon should be familiar with the end-to-end microvascular anastomotic technique.

End-to-end anastomoses begin by meticulous vessel preparation. The vessels are handled using jewelers forceps by grasping only the adventitia. The closing

Figure 23 Bird's eye view of a typical microvascular instrument table. It is a comparatively simple set-up with straight and curved microvascular needle holders and pick-ups. A 10 cc syringe is supplied with a 22 gauge angiocatheter for intermittent heparin-saline irrigation. A variety of microvascular temporary occlusion clips are also supplied in the case on the upper right corner of the table.

Figure 23 Bird's eye view of a typical microvascular instrument table. It is a comparatively simple set-up with straight and curved microvascular needle holders and pick-ups. A 10 cc syringe is supplied with a 22 gauge angiocatheter for intermittent heparin-saline irrigation. A variety of microvascular temporary occlusion clips are also supplied in the case on the upper right corner of the table.

forces generated by arterial clamps correlate with the extent of intimal injury and thrombogenic potential. Therefore, vascular occlusion clamps are applied with only enough pressure to occlude blood flow. The donor and recipient vessels can be clamped independently or a framed clamp (clamps joined by two parallel bars) may be used to keep the vessel ends in alignment. The adventitia is strongly throm-bogenic, so it is removed from around the area of the proposed anastomoses using the curved microvascular scissors. Heparinized saline irrigation (100 U/cc) is applied to each lumen to keep them clear of clots and debris. Papaverine (30-40 mg/cc) or 2% lidocaine can be applied to minimize vessel spasm. The vessel ends are gently dilated with a spatulate dilator forceps. Depending on the diameter of the vessel, an atraumatic nylon suture is chosen between 8-0 and 10-0. Carrell's -g triangulation method of suture placement is popular. Three stay sutures are placed initially to approximate the vessel ends 120 degrees apart. As the stay sutures (two »

at a time) are pulled taut, the back wall tends to fall away facilitating accurate placement (Fig. 24). Sutures are placed by continually halving the distance between the ^ apposing sutures to achieve a watertight seal. The needle must pass through the media and intima at a right angle approximately two vessel thicknesses away from the edge. The posterior edge is accessed for suture placement by flipping the vascular clamps 180 degrees. Problems that may lead to thrombosis include inadvertent § suture placement through the back wall of the vessel, rough handling, failure to

Figure 24 The triangulation method of microvascular suture placement is convenient since the 120 degree offset of the sutures allows the back wall of the vessel to fall away, thereby avoiding inadvertent suture placement through it.

include a slightly separated intima with the stitch, and inclusion of a significant amount of adventitia within the vessel lumen. The venous anastomosis is slightly more difficult than the arterial anastomosis because the walls of the veins are thinner and collapsible; however, fewer sutures are required. The venous clamps are released first. Arterial leakage is common but will usually subside. Brisk bleeding will require the placement of additional sutures. Re-endothelialization along the suture line begins by day 3 and is complete by day 7 in the veins and arteries.

Vessel size mismatch is better tolerated on the venous side where mismatches up to 2:1 are acceptable. Cutting the smaller vein at an angle allows end-to-end approximation but greater mismatches are best handled by an end-to-side anastomosis. The usual problem on the arterial side is that the donor artery is much smaller than most of the branches of the external carotid artery. End-to-side anastomoses are generally not performed on the arterial side because of technical limitations and connecting to the common or internal carotid system is contraindicated because of the risk of thrombosis.

Interrupted sutures are preferred but a continuous suture technique is feasible for both the artery and vein. Continuous suturing is reserved for larger vessels with a diameter of at least 2 mm because the continuous suture narrows the lumen. A continuous suture technique is most applicable to large veins where slight luminal narrow is insignificant and tight approximation is not critical. Interpositional vein grafts can be used to bridge arterial and venous gaps, with comparable success to single anastomoses. Vein grafts must be reversed so that the valves do not obstruct flow.

A useful alternative to suture for the venous anastomosis is a stapling device (e.g., 3M Coupler). The end of each vein is pulled through a plastic ring and spread over protruding prongs that penetrate and secure the veins. The opposing plastic rings are approximated and secured by penetration of the prongs into the opposite ring. These devices are indicated only for the venous anastomosis. Anastomotic time is significantly reduced and animal studies show that patency rates are equivalent to hand-sewn anastomoses.

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