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The thoracodorsal artery perforator or TAP flap is
a fasciocutaneous flap based on a musculocutaneous perforator or perforators
from the thoracodorsal vessel axis and/or its vertical branch derivative. In
contrast to the other well-known DIEP (deep inferior epigastric perforator) and
SGAP (superior gluteal artery perforator) flaps that provide
bulk, the TAP flap provides a relatively thin and pliable skin paddle. In a
reasonably thin person, the flap ranges from 1 – 2 cm in thickness. In heavier
patients the flap may be thinned by delaminating the deep adipose layer from the
superficial adipose layer at the level of the superficial fascia. The resulting
thickness of the skin and superficial fat layer will be approximately 1 cm. The
TAP flap is well suited for extremity, head and neck, and peri-articular
resurfacing as well as for the contouring of shallow defects. As is the case
with other perforator flaps, the surgical dissection can be difficult.
A flap of dimensions 15 X 8 cm can be harvested on
a single perforator. These dimensions allow for both primary closure of the
donor site and avoidance of post-operative venous congestion in the flap.
Anatomy
After originating from the subscapular axis, the
thoracodorsal vessels course toward the latissimus dorsi. On reaching the deep
surface of the muscle, the thoracodorsal vessels most commonly divide into two
primary muscular branches: the medial or horizontal branch, and the lateral or
vertical branch. These branches usually diverge at approximately 45 degree
angles to one another. Both course initially on the deep surface of the muscle
eventually becoming intramuscular more distally. The lateral branch courses
vertically and 2 - 3 cm inside the lateral border of the latissimus. A
perforator or combination of perforators off the distal main thoracodorsal
and/or it’s lateral branch constitute the vascular supply of the TAP flap.
The first perforator is located approximately 6 – 8
cm below the posterior axillary fold and may be either a branch of the distal
main thoracodorsal or arise from it’s lateral branch. Subsequent perforators, up
to a total of three, arise at 1.5 – 4 cm intervals inferiorly off the lateral
branch. Each perforator displays a 3 – 5 cm oblique course through the substance
of the muscle giving off numerous muscular branches before penetrating through
the dorsal thoracic fascia to supply the overlying skin and subcutaneous fat
layers. Each perforating artery is 0.3 - 0.6 mm in diameter and accompanied by
two venae comitans.
Operative Technique
The patient is placed in the lateral decubitus
position on a beanbag. The ipsilateral arm is left free and included in the
operative scrub. A stockinette around the arm and Mayo stand with a well-padded
pillow helps to rest and optimally position the arm during surgery.
The lateral border of the latissimus is palpably
identified and outlined with a marking pen. With the arm placed at the patient’s
side, a sterile pencil doppler is used to identify and map out the perforators
starting about 6 – 8 cm below the posterior axillary fold and 2 – 4 cm inside
the lateral border of the latissimus. Additional perforators are identified at
1.5 – 4.0 cm intervals inferior to the first.
A flap of dimensions approximating 8 X 15 cm,
centered over the perforators is outlined. This results in an ellipse with its
anterior longitudinal arc skirting the lateral border of the latissimus.
The width is determined by the pinch test to determine what can be closed
primarily. The maximum reliable length of a TAP flap that can be elevated on a
single perforator has not been clearly established. Flaps up to 25 cm in length
have been reported.
The anterior incision is made first. The anterior
margin of the latissimus is identified. Scissor dissection then proceeds in an
anterior to posterior direction gently separating the dorsal thoracic fascia
from the underlying muscle using vertical spreads. All perforators are
identified and protected. A cutaneous nerve may be seen accompanying the largest
perforator. The dominant perforator is selected and the others can be ligated.
Alternatively, if a second perforator appears to be in the same longitudinal
plane as the first, it is likely that it is a more distal branch of the same
intramuscular vessel and can be included with only a small additional time
investment. Also, if all perforators are small, it seems prudent to include more
than one.
The perforator or perforators are chased through
the substance of the muscle toward their origin from the distal thoracodorsal or
its lateral branch, which may be intramuscular at this point. Bipolar cautery is
used to ligate the multiple small muscular branches that are present during all
stages of the dissection. Cautious use of mini sel-retaining retractors
within extended longitudinal muscle splits on each side of the perforator(s)
greatly facilitates the dissection. When the perforator has been dissected 2 – 3 cm
within the muscle the posterior skin incision is completed thus isolating the
fasciocutaneous ellipse on its pedicle. This not only allows the skin
flap to be manipulated in order to facilitate completion of the dissection but
also allows flap perfusion to be confirmed before the blood supply to the
potential fall back latissimus muscle flap has been compromised.
With flap perfusion deemed adequate, dissection
continues through the latissimus. If the source of the perforator is the distal
main thoracodorsal trunk, this vessel is easily identified proximally on the
deep surface of the muscle.
The vessels distal to the perforator are clipped
after care is taken to separate the accompanying thoracodorsal nerve. The
proximal vessels are also separated from the nerve and the desired length of
thoracodorsal pedicle liberated. The vessels are ligated, and with gentle
traction on the flap are simply pulled through the split in the muscle.
If the source of the perforator is the lateral
branch of the thoracodorsal, its intramuscular path is traced proximally until
its course on the deep surface of the muscle is revealed. The lateral
branch of the thoracodorsal is then dissected off the deep surface of the muscle
and traced proximally to its junction with the main axis and the
medial/horizontal branch. If adequate pedicle length and vessel diameter are
present, the pedicle may be divided here. If a longer pedicle with larger
diameter vessels is necessary, the medial/horizontal branch is ligated and
dissection proceeds up the main thoracodorsal axis as required. Caution,
accompanying the lateral branch of the thoracodorsal vascular axis are branches
of the thoracodorsal nerve. More proximal nerve branches to muscle can usually
be preserved by separating the nerve from the pedicle. Distally, the
perforator becomes so small that separating the nerve at this level could prove
disastrous. Therefore, at some point, the distal intramuscular branches of the thoracodorsal nerve accompanying the perforator must be sacrificed and left
adherent to the pedicle. This trivial amount of deinnervation is surely
inconsequential. If there is a desire to neurotize the flap the previously
mentioned cutaneous nerve can be separated off the main nerve branches
proximally by intrafascicular dissection.
The edges of the vertical muscle split are
approximated with absorbable suture. Closure of the back wound proceeds in the
usual fashion.
References
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Angrigiani, C., Gilli, D., and Siebert, J.
Latissimus dorsi musculocutaneous flap without muscle. Plast. Reconstr. Surg.
96: 7: 1608-1614: 1995.
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Kim, J.T., Koo, B.S., and Kim, S.K. The thin
latissimus dorsi perforator-based free flap for resurfacing. Plast. Reconstr.
Surg. 107: 2: 374-382: 2001.
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Rowsell, A.R., Eisenberg, N., Davies, D.M., and
Taylor, G.I. The anatomy of the thoracodorsal artery within the latissimus
dorsi muscle. Br. J. Plast. Surg. 39: 206-209: 1986.
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Spinelli. H.M., Fink, J.A., and Muzaffar, A.R.
The latissimus dorsi perforator-based fasciocutaneous flap. Ann. Plast. Surg.
37: 5: 500-506: 1996.
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