and Frank Hölzle2
Department of Oral and Maxillofacial Surgery, Klinikum rechts der Isar, Technische Universität Munich, Munich, Germany
Department of Oral and Maxillofacial Surgery, University Hospital of RWTH Aachen University, Aachen, Germany
Electronic supplementary material
The online version of this chapter (doi:10.1007/978-3-319-53670-5_6) contains supplementary material, which is available to authorized users.
6.1 Development and Indications
As the first myocutaneous flap, the latissimus dorsi flap was described already in 1896 by Tansini  and used for defect coverage following radical mastectomy by D’Este in 1912 . Despite its excellent suitability for chest wall reconstruction, the flap did not become popular until the 1970s, when a number of publications appeared, in which the previously described advantages were confirmed and further indications for defect coverage in the area of the shoulder and arm were proposed [57, 58, 348, 357, 366, 387, 408, 500]. The first application of a pedicled latissimus dorsi flap for reconstruction in the head and neck area was described by Quillen in 1978 , whereas the microvascular transfer of this flap was performed by Watson in 1979 . In further publications, the reliability and safety of this flap, especially its usefulness for reconstructions in the head and neck area, was demonstrated [201, 351, 352, 435, 438, 496, 578]. In all these reports, a great variety of application possibilities was described. This broad indicational spectrum was possible because of the large amount of tissue available, offering various possibilities for changing the flap design, and the long and high-caliber vascular pedicle, making microvascular anastomoses technically easy [389, 435, 438, 442]. A particular indication of the latissimus dorsi flap is the covering of large perforating defects of the oral cavity, using two skin paddles, which can be outlined along the transverse and vertical branch of the thoracodorsal artery [30, 209, 341, 389]. The inclusion of a rib allows for an osteomyocutaneous transfer and was proposed for the reconstruction of the mandible or other parts of the facial skeleton [221, 333, 342]. Another indication of this broad and flat muscle is reconstruction of the scalp, especially when used as a muscle-only flap, which is covered by a skin graft [174, 389, 442, 517], or as a myofascial flap to cover defects at the skull base . Motor reinnervation of the muscle flap has been described by Harii, who connected the thoracodorsal nerve to the facial nerve for rehabilitation of the paralyzed face . For tongue reconstruction, an anastomosis to the hypoglossal nerve was performed [231, 438]. After de-epithelization, musculo-subcutaneous flaps are obtained, which were used for contour augmentations in the head and neck area [131, 389, 438]. Apart from applications in the head and neck area, a lot of other useful indications exist for this very popular free flap, such as reconstructions of the female breast [57, 100, 283], chest wall and axilla [18, 348, 357], shoulder and upper extremity [311, 328], closure of hernias of the diaphragm , or other intrathoracic defects [91, 95, 495]. Moreover, defect coverages at the lower extremities [57, 112], the sacrum , and treatments of chronic osteomyelitis have been performed using this flap [14, 219].
The latissimus dorsi is a flat, fan-like muscle which arises directly from the spinal processes of the lower six thoracic vertebrae, the lumbar and sacral vertebrae, and the dorsal iliac crest via the thoracolumbar fascia. The muscle inserts between the teres and pectoralis muscles at the humerus, and together with the teres major, it forms the posterior axillary fold. The main nutrient vessel is the thoracodorsal artery, which like the circumflex scapular artery, arises from the subscapular artery. The vascular pedicle travels along the lateral thoracic wall at the undersurface of the latissimus muscle, regularly giving off a strong branch to the serratus anterior muscle. This serratus branch can serve as the vascular pedicle if the thoracodorsal vessels have to be sacrificed during axillary lymph node extirpation [33, 149, 546]. The length of the extramuscular part of the vessel course varies from 6 to 16 cm, being about 9 cm in average . Apart from the aforementioned branch to the serratus muscle, on its extramuscular course, the pedicle is giving off regularly another branch to the inferior angle of scapula, mostly just proximal to the serratus branch . This scapular branch is coursing in the fascial gliding layer between the serratus, subscapularis, and teres major muscle to the scapular bone. Thus, an isolated bone flap from the tip of the scapula which is nourished from the vascular system of the thoracodorsal artery can be raised, and the vascular pedicle of this inferior angle scapular bone flap is about 15 cm on average . Further minor vessels are given off to the teres and subscapularis muscles. The neurovascular hilum where the pedicle enters at the undersurface of the latissimus is 1.5–3 cm away from the anterior muscle rim. At the point of origin from the subscapularis vessels, the thoracodorsal vessels have diameters of 1.5–4 mm (artery) and 3–5 mm (vein after unification of the two concomitant veins) . Whereas the thoracodorsal artery mainly provides blood supply to the proximal and lateral two thirds of the muscle, the distal parts of the latissimus dorsi are reached by perforating branches of the intercostal arteries . Thus, blood supply to the flap can become tenuous when harvested from the distal and medial parts of the muscle. The intramuscular course of the thoracodorsal artery, which is directly accompanied by the thoracodorsal nerve, was investigated in detail by Tobin et al.  and Bartlett et al. . According to their findings, shortly after entering the muscle the main vessel divides into a vertical branch, which runs parallel to the anterior border of the muscle, and a transversal branch, which runs parallel to the proximal muscle rim. With 94.5%  and 86% , this vascular pattern was found to be present in the vast majority of all cases. This constant vascular anatomy is giving the basis for dividing the flap into two separate skin paddles and two neuromuscular units. Acryl injections into the arterial system have additionally shown that multiple secondary branches arise from the transversal and vertical branches to the surface of the muscle, forming a dense network of anastomoses [448, 449]. This network allows thinning of the flap by removal of the superficial muscle layers without endangering blood supply [71, 450]. Although skin paddles can be designed over any part of the muscle, blood supply can become critical at the caudal and medial parts, where only a few perforating vessels to the skin where found. The highest density of myocutaneous vessels and thus the preferable region for outlining skin paddles is parallel to the anterior or cranial borders of the muscle [33, 546]. Nevertheless, up to 10 cm long extended skin flap can be built over the distal part of the latissimus muscle, which is safely perfused by myocutaneous perforators from a proximal myocutaneous portion of the flap . Because of the high density of myocutaneous perforating vessels, large skin paddles can be built along the anterior muscle border, harvesting only a narrow strip of muscle which contains the vascular pedicle . Although from an anatomical point of view flap dimensions can be extended as far as 30 × 40 cm , the ability to achieve direct wound closure limits the size of the flap; thus, depending on the patient’s body shape, flap width should not exceed 10 cm . In addition to this wide and safe perfusion of the latissimus muscle and overlying skin, the thoracodorsal artery contributes to the blood supply of the scapular bone, which was investigated by Coleman and Sultan . According to their findings, an angular branch, nourishing the tip of the scapula, branches off from the thoracodorsal artery just proximal to the serratus branch (58%) or from the serratus branch directly (42%), allowing an osteomyocutaneous transfer of the latissimus dorsi flap. This extension of flap raising can be useful for reconstruction of the anterior mandible by giving the bone a horizontal orientation to replace the interforaminal segment .
There are only few variations of the vascular anatomy described in the literature, none of them affecting the possibility of raising the flap. Whereas the subscapular artery and vein arise close to each other from the axillary vessels in the majority of patients, the subscapular artery can have a distance of up to 4 cm from the vein in seldom cases. Moreover, the thoracodorsal artery may spring off directly from the axillary artery . Satoh et al. described a seldom variation of blood supply to the latissimus dorsi in a clinical case, where the vascular pedicle was only rudimentally present, so that anastomoses had to be performed to the circumflex scapular vessels, which were found to perfuse the muscle instead of the thoracodorsal vessels .
6.3 Advantages and Disadvantages
The advantages of the latissimus dorsi flap overcome its few disadvantages very clearly: Because of its constant vascular anatomy, the high density of myocutaneous perforators to the overlying skin, the relatively long and high-caliber vessels, and the ease of flap raising, the latissimus dorsi is a popular and safe flap, offering numerous possibilities for defect coverage. Normally, the morbidity of the donor site is low, but can increase after having simultaneously performed a radical neck dissection sacrificing the accessory nerve. Under these circumstances, stability of the shoulder can be reduced . Although some reduction of strength and function of the shoulder is generally not noted by most patients, some sports and physical activities can be negatively affected [283, 302, 437]. Whereas Laitung and Peck could find a good compensation of the latissimus function by other muscle groups even in physically active patients , Russel and coworkers noted a weakness of all muscles surrounding the operated shoulder . The most significant disadvantage of the latissimus dorsi flap is the difficulty of flap raising simultaneous to tumor resection in the head and neck area [19, 406]. When bringing the patient in a lateral decubitus position prior to flap harvesting, care must be taken to stabilize the contralateral shoulder to prevent injury to the brachial plexus [351, 636]; otherwise, a weakness or paralysis of the radial nerve  or a permanent loss of sensibility  or complete motor function  at the upper extremity can occur. If the donor site has to be covered by a skin graft, the aesthetic result is always poor, so flaps should not be outlined broader than 10 cm [333, 406]. When a muscle flap is needed, harvesting can be performed using an endoscopic-assisted approach, only creating a small incision in the axillary pit . Despite the flat shape of the muscle, the myocutaneous latissimus dorsi flap is often too bulky for small and medium-sized defects of the oral cavity, because a considerable layer of adipose tissue between muscle and skin is found in many patients. When used for facial contour augmentation, the subsequent atrophy of the muscle component can lead to unfavorable secondary volume loss .
6.4 Patient Positioning
The patient is brought in a lateral decubitus position and a pad is placed between the shoulder and the neck on the contralateral side to prevent impingement of the brachial plexus by the clavicle. The ipsilateral arm is included in the operating field to allow for free movement, and prepped and draped together with the lateral thorax, shoulder, axilla, and back. If the patient is in prone position, which is also possible for flap raising, reprepping and redraping must be performed before the operation is continued with the patient in supine position.
6.5 Flap Design
Although skin paddles can be designed with a high variability over the whole proximal two thirds of the muscle, in a standard situation it is highly recommended to outline the skin paddle over its anterior part with the flap axis running 4–5 cm dorsal to the anterior edge of the latissimus dorsi. The anterior border of the skin paddle should not exceed the rim of the muscle, and the flap width should be limited to 10 cm to allow primary closure. For exposure of the pedicle, a straight incision is marked from the proximal pole of the flap to the axilla. Correct placement of the skin paddle must carefully be checked by palpating the anterior muscle rim, which forms the posterior demarcation of the axillary groove. Because of the constant anatomy of the pedicle and the high number of perforators, no preoperative measures are necessary before flap raising, if no previous surgery (lymphadenectomy) has been performed in the axilla (◘ Figs. 6.1, 6.2 and 6.3).
Skin Incision and Exposure of Anterior Rim of Latissimus Dorsi Muscle
The initial incision is made along the anterior border of the skin paddle and continued into the axilla from the upper pole of the flap. The subcutaneous fatty tissue, the amount of which can considerably vary, is transected perpendicularly until the muscle fibers are reached. The anterior rim of the latissimus muscle is exposed by dissecting the fatty tissue away from the serratus muscle and retracting it in an anterior direction. The fat underlying the skin paddle may not be separated from the latissimus muscle (◘ Figs. 6.4 and 6.5).
Identification of Anterior Muscle Rim and Serratus Branch
Having the anterior border of the latissimus clearly identified, by further retracting the skin and subcutaneous fatty tissue in an anterior direction, a branch of the thoracodorsal artery is exposed which supplies the serratus anterior muscle. This strong vessel is the first branch of the thoracodorsal artery which becomes visible. The serratus branch now is traced proximally, leading directly to the vascular pedicle. Additionally, the thoracodorsal artery can easily be located by palpating its pulsation underneath the proximal muscle rim (◘ Fig. 6.6).
Dissection of Neurovascular Pedicle and Side Branches
The anterior rim of the muscle is elevated and retracted, so that dissection of the vascular pedicle can be carried out. The serratus branch which is leading to the thoracodorsal vessels is preserved until the end of flap raising. Now, dissection of the pedicle is performed in the cranial direction. A second side branch of the thoracodorsal vessels becomes visible opposite to the serratus branch, which is running to the inferior angle of the scapula. Depending of the desired pedicle length, the thoracodorsal vessels are followed up to the axilla, until the circumflex scapula vessels are reached. Dissecting caudally, the neurovascular hilum is found about 2–4 cm distal to the serratus branch, where the thoracodorsal vessels are entering the muscle at its undersurface. Here, the vein is located lateral to the artery, and the motor nerve is running between the vessels (◘ Figs. 6.7 and 6.8).
Undermining of the Latissimus Dorsi Muscle
A vessel loop is placed around the neurovascular pedicle inferior to the serratus and scapula branch, and the latissimus dorsi muscle is further undermined by blunt dissection. Careful hemostasis is necessary, especially in the distal and medial parts, where segmental branches of the lumbar artery are additionally supplying the latissimus dorsi muscle (◘ Fig. 6.9).
Muscle Transection at Inferior Flap Pole, Complete Circumcision of Skin Paddle
The skin paddle is now completely peritomized to the muscle fascia. The muscle is elevated, and then transection of the muscle fibers is performed along the inferior pole of the flap. Because the anterior border of the skin paddle corresponds with the anterior muscle rim, the muscle must not be transected along the anterior periphery of the flap (◘ Fig. 6.10).
Further Elevation of Latissimus Muscle
The posterior parts of the latissimus muscle can now easily be undermined, and the fibro-fatty tissue between the latissimus and the serratus muscle is divided (◘ Fig. 6.11).
Transecting the Latissimus Dorsi Muscle Along the Posterior Periphery of the Flap
According to the dimensions of the skin paddle, the muscle is incised along its posterior periphery. The neurovascular pedicle is slightly retracted from the muscle to exactly visualize the neurovascular hilum in the region of the cranial pole of the flap (◘ Fig. 6.12).
Complete Division of Muscle Fibers Superior of Flap Hilum
The latissimus dorsi now is completely divided cranial to the neurovascular hilum, creating a strip of muscle between the cranial pole of the skin paddle and the vascular hilum, which carries the anterior branch of the thoracodorsal vessels. The horizontal branch travelling along the superior border of the latissimus dorsi muscle is transected at the cranial flap pole shortly after the bifurcation of the thoracodorsal vessels. To ensure safe protection of the anterior branch, which runs 1.5–3 cm away from the anterior border, this strip of muscle should be about 4–5 cm broad (◘ Fig. 6.13).