Neurovascular Anatomy

The subscapular artery branches within a few millimeters of its origin from the axial artery into the circumflex scapular artery and the thoracodorsal artery. The triangular space is the essential anatomical landmark for the system of flaps nourished by the circumflex scapular artery. The long head of the triceps, teres minor muscle, and teres major muscle form the boundaries of the space. Deep within the triangular space, the circumflex artery gives off several ascending and descending branches along the lateral border of the scapula to supply the periosteum and underlying bone. As the artery exits the triangle, it divides into transverse and descending branches to supply the transverse and parascapular fasciocutaneous flaps, respectively. The transverse flap tends to be a slightly better color match to the face and neck but the dimensions must be smaller than a parascapular flap to allow primary closure of the donor site. A transverse flap can be up to 6 x 15 cm while a parascap-ular flap can be much larger depending on the size and habitus of the patient. The length of the vascular pedicle including the subscapular artery ranges from 6 to 8 cm and the individual components (bone and skin flaps) can be freely manipulated based on their respective vascular pedicles.

The thoracodorsal artery does not exit the triangular space but continues infer-iorly behind the teres major muscle to travel deep to the latissimus muscle. A branch to the serratus anterior muscle is found at approximately the inferior border of the teres major muscle. The angular artery branches off the artery to the serratus to supply the tip and lower third of the scapula. This portion of the scapula can be harvested with the thoracodorsal system or it can be preserved with the circumflex scapular system. If it is preserved with the circumflex scapular system, the lower third of the scapula will be vascularized despite osteotomies that would otherwise place this segment at risk. The artery to the serratus anterior continues on to supply the lower three or four slips of the serratus anterior. The lateral thoracic artery supplies the upper five slips of the serratus anterior muscle. Injection studies demonstrate that the thoracodorsal artery provides reliable vascularity to the sixth and seventh ribs at the origin of the serratus muscle (62). A twig from the long thoracic nerve and a segmental branch of the artery supply each slip of muscle. The thoraco-dorsal artery penetrates the deep surface of the latissimus muscle approximately 10 cm from the axillary artery, well inferior to its insertion into the humerus (at the intertubercular groove). After penetrating the latissimus muscle, the thoracodor-sal artery splits into a lateral branch that parallels the anterior border of the muscle and a medial branch that courses inferomedially.

No harvestable sensory nerves are described for any component of the scapular |

system. Most components have two veins accompanying the artery (the venae comi-tantes) that measure between 1.5 and 3 mm. The venae comitantes usually merge into c a single large vein near the subscapular artery. ^

Surgical Highlights g

The Fasciocutaneous Flaps and the Osteocutaneous Scapular Flap. As for all of o the scapular flaps, the patient must be placed in the lateral decubitus position for flap harvest. The ipsilateral arm can be gently supported over a sterilely covered Mayo stand with generous cushioning around the elbow. An axillary roll should be placed under the opposite shoulder and axilla to prevent a neuropraxic injury. The key surface landmark is the triangular space bounded by the long head of the triceps, the teres major muscle, and the teres minor muscle (Fig. 52). It is palpated with the thumb as the axilla is grasped and the arm is extended (Fig. 53). The circumflex scapular artery passes through this space to supply the transverse and parascapular fasciocutaneous components. En route through the space, the artery sends periosteal branches to the lateral border of the scapular. The transverse and parascapular fasciocutaneous flaps can be harvested as separate components based on the transverse and descending branches of the circumflex scapular vascular bundle. The lateral aspect of the flap must be placed over the triangular space to capture the circumflex artery as it exits the triangular space. A parascapular flap, due to its oblique orientation on the back, can be designed much larger (up to 12 cm x 20 cm) than its counterpart, the transverse scapular flap, while still allowing primary donor site closure. Dissection begins medially by raising the flap (including its underlying fascia) towards the triangular space. The fasciocutaneous vessels (transverse and descending branches of the circumflex scapular) are visualized on the undersurface of the flap while the thick white deep fascia over the infraspinatus muscle is left undisturbed. Once the vessels are seen diving into the triangular space, the fasciocuta-neous flap is raised circumferentially, pedicled only by its vascular supply (Fig. 54). The periosteal branches to the scapular bone are divided and the teres minor and major and triceps muscles are retracted. The circumflex scapular vessels are dissected to their origin from the subscapular artery where they are divided, thereby harvesting the skin flap and its attached vascular pedicle.

Figure 52 A large parascapular flap marked over the back. The dimensions of a parascapular flap can be much greater than a transverse flap, while still allowing for primary closure of the donor site.
Figure 53 Seeking the triangular space with the thumb. This is the first step to determine the exit point of the feeding vessels. The skin flaps must be harvested to include the skin and subcutaneous tissues over this space.
Figure 54 The transverse scapular flap harvested and pedicled on the circumflex scapular vessels. Note the origin of the vessels through the triangular space.

Harvest of an osteocutaneous scapular flap requires that the periosteal branches to the lateral border of the scapula be preserved while the pedicle is being dissected toward the subscapular artery. To harvest the bone, a cautery device is used to incise the teres and infraspinatus muscles sharply along a line approximately 2 cm from the lateral scapular border. The glenoid fossa is palpated and an oscillating saw is used to cut along the line previously outlined by cautery. A transverse osteotomy is made 2 cm below the glenoid fossa, thereby completing the bony cuts. Once the bone is pulled laterally, it will be noted that muscular slips from the serra-tus anterior and subscapularis must also be divided with cautery. The angular artery enters the tip of the scapula and should be preserved if conforming osteotomies are planned. This artery is a branch from the artery to the serratus anterior muscle (a division of the thoracodorsal artery). The artery to the serratus muscle is divided distal to the take-off of the angular branch (Fig. 55). The osteocutaneous flap is finally freed by dividing the subscapular artery. The circumflex scapular and thoracodorsal arteries should be carefully preserved. After harvesting the flap, the cut teres muscles

Figure 55 The parascapular skin flap harvested with the scapular bone (osteocutaneous scapular flap). Note that the bone consists of only the lateral border of the scapular bone. The bone along the tip of the scapular is prone to necrosis only if a shaping osteotomy is created that isolates the tip from its vascular supply. To ensure adequate vascularity of this segment of bone in the event of osteotomy, the angular artery should be preserved (see text).

Figure 55 The parascapular skin flap harvested with the scapular bone (osteocutaneous scapular flap). Note that the bone consists of only the lateral border of the scapular bone. The bone along the tip of the scapular is prone to necrosis only if a shaping osteotomy is created that isolates the tip from its vascular supply. To ensure adequate vascularity of this segment of bone in the event of osteotomy, the angular artery should be preserved (see text).

are not sutured together but are left in situ to prevent shoulder stiffness postoperatively. The serratus muscle fibers may be reattached to the inferior aspect of the scapula to stabilize this structure, if needed.

The Latissimus Musculocutaneous Flap. The latissimus muscle is harvested via an access incision along the posterior axillary fold. The extent of the incision depends on the volume of muscle to be harvested and whether a muscle-only or a musculocutaneous flap is planned (Fig. 56). The anterior border of the muscle is retracted and the neurovascular anatomy is exposed (Figs. 57, 58). If a segment of muscle is going to be used for facial reanimation, the thoracodorsal nerve is dissected free and traced superiorly to deep within the axilla near the axillary artery. Additional length on the nerve can be achieved by dissection of the nerve distally toward the muscle and division of small twigs until the main body of the nerve actually penetrates the segment of muscle that will be transferred. The length of nerve that can be harvested is up to 15 cm. The segment of muscle should be 3-4 cm wide by 810 cm long, with the direction of the fibers paralleling the long axis. The vascular pedicle is dissected proximally to the subscapular artery and divided. The muscle is inset into the face in the typical manner (see section on gracilis muscle) from the zygoma to the modiolus and inferior lip. The thoracodorsal nerve is placed through a subcutaneous pocket in the upper lip to the preauricular area over the opposite cheek. The thoracodorsal nerve is anastomosed end-to-end with two or three buccal branches of the facial nerve.

When harvesting the latissimus muscle with or without the overlying skin, the thoracodorsal vascular pedicle should be identified first through the upper part of the access incision. This simplifies the dissection because the vascular pedicle enters the muscle well inferior to, and at a variable distance from, its insertion into the upper humerus. A muscle-only flap is harvested by dissecting the subcutaneous tissues of the surface of the latissimus muscle while identifying the entire anterior

Figure 56 After a lengthy longitudinal incision along the axillary fold corresponding to the anterior border of the latissimus muscle, anterior and posterior subcutaneous flaps are raised over the muscle outside the intended skin paddle. The skin paddle must be of sufficient size to capture the terminal musculocutaneous vessels that nourish it.

Figure 56 After a lengthy longitudinal incision along the axillary fold corresponding to the anterior border of the latissimus muscle, anterior and posterior subcutaneous flaps are raised over the muscle outside the intended skin paddle. The skin paddle must be of sufficient size to capture the terminal musculocutaneous vessels that nourish it.

Figure 57 Retraction of the anterior border of the latissimus muscle uncovers the relevant neurovascular anatomy. Note the surface neurovascular structures over the serratus muscle including the long thoracic nerve and serratus vessels. The thoracodorsal vessels supplying the latissimus muscle are large and easily identified.

Figure 57 Retraction of the anterior border of the latissimus muscle uncovers the relevant neurovascular anatomy. Note the surface neurovascular structures over the serratus muscle including the long thoracic nerve and serratus vessels. The thoracodorsal vessels supplying the latissimus muscle are large and easily identified.

edge of the muscle. The thoracodorsal pedicle is identified as mentioned by retracting the humeral head of the muscle and a vessel loop is placed around the vascular pedicle. The natural tissue plane between the underlying muscles and fascia including the serratus muscle is bluntly dissected. The vascular pedicle is separated from the thor-acodorsal nerve and dissected superiorly to the subscapular artery after the branch to the serratus muscle is divided. The humeral head of the muscle is divided using cautery. The muscle is freed by dividing its inferomedial insertions and, finally, dividing the subscapular artery and thoracodorsal nerve.

To harvest a musculocutaneous flap, a skin island is designed that is completely within the boundary of the latissimus muscle since any portion of the skin that extends beyond the muscle is subject to ischemia and necrosis. The skin paddle should be no less than 25 cm2 to ensure the inclusion of sufficient musculocutaneous perforating vessels. The outline of the skin island is sharply incised to (not through) the underlying muscle. A subcutaneous dissection over the muscle proceeds outside the borders of the skin island. The anterior edge of the latissimus muscle is identified through the posterior axillary incision and the dissection proceeds as in a muscle-only harvest.

Primary closure over one or two large suction drains is typical. The subcutaneous tissues are closed with strong absorbable sutures and the skin is closed with staples supplemented with horizontal mattress nonabsorbable sutures. This harvest site is especially prone to the formation of seromas; therefore, the drains should remain in place for 10 days. Some collection of fluid is to be expected after the drains •§, are removed but the strong closure should prevent dehiscence of the wound.

The Serratus Anterior Muscle for Facial Reanimation. The anterior border of the >3

latissimus muscle is identified through the posterior axillary fold incision. The serra-tus muscle is exposed by posterior retraction of the latissimus muscle, blunt dissection, and subcutaneous dissection over the muscle itself. The neurovascular components are easily identified since they enter the muscle from its outer surface.

The thoracodorsal vessels are divided distal to the take-off of the serratus branch. The serratus branch supplies only the lower three or four slips of the muscle and these slips of muscle will be harvested. The long thoracic nerve is split with respect to its segmental innervation of each muscular slip with the aid of a nerve stimulator. The muscular slips to be harvested are separated from their site of origin (underlying rib) and insertion (scapula) and freed (Fig. 58). The thoracodorsal nerve is divided proximally and the serratus and thoracodorsal vessels are dissected towards the subscapular artery and divided. Donor site closure is accomplished through simple layered approximation of the subcutaneous and cutaneous tissues over a suction drain.

The slips of the serratus muscle can be used to rehabilitate separate functioning units of the face. Cross-face nerve grafting is usually required several months prior to flap transfer. Immediate anastomosis with the hypoglossal nerve is also described (63).

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