Keywords
cadaveric - anatomy - sural artery perforator flap - gastrocnemius muscle
Introduction
Taylor & Daniel[1] first suggested the medial sural vessels as the basis of a new flap donor site in
1975 and, two decades later, Montegut[2] presented the first clinical cases of the medial sural artery perforator flap. Subsequently,
Cavadas[3] and other authors[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11] reported small clinical series of its use and emphasized its many advantages and
limited donor morbidity. In situations when a thin and pliable flap is needed, the
radial forearm flap has traditionally been the choice flap.[12] The medial sural artery perforator flap is comparable to the radial forearm flap
in its thinness and pliability. It is therefore a suitable alternative for such defects
with much lower donor site morbidity. The medial sural artery perforator flap is,
however, more technically demanding, with a need for intramuscular dissection to raise
the flap. Compounded by the lack of clearly described surgical anatomy of the flap,
many surgeons have avoided utilizing this flap. Previous anatomic studies have sought
to identify the locations of the medial sural artery perforators. Although their approximate
vertical distances from the popliteal crease have been described, it remains difficult
to predict its location preoperatively. This is particularly important when a small
flap is needed, as the flap needs to be centered exactly over the dominant perforator.
This study aimed to further clarify the vascular anatomy of this flap and identify
the most consistent major perforator to facilitate safer flap harvesting.
Methods and Materials
Ten lower limbs from fresh adult cadavers were injected with red latex. The limbs
were positioned prone with the knee extended, and subfascial dissection was begun
from the posterior midline and advanced medially. The number of major (subfascial
diameter >1.0 mm) and minor perforators were noted. The vertical distance from the
popliteal crease and the horizontal distance from the posterior midline of the leg
were recorded in centimeters. Each sizable perforator was followed by intramuscular
dissection to its origin, and the pedicle length was recorded.
Results
An average of 4.4 perforators (range = 3 to 8) was found to pierce the medial gastrocnemius
muscle in each lower limb. At least one major perforator was identified in all specimens
(mean = 2). Eight of ten legs had two or more sizable perforators.
The medial sural artery originated from the popliteal artery. After running for a
distance of 3 to 6 cm, the medial sural artery typically divided into two branches
(a medial and lateral branch) within the substance of the medial gastrocnemius muscle.
In one specimen, the medial sural artery did not give off any divisions and in another
it was observed to divide into three branches. Perforators were given off at intervals
along the course of each branch, and these musculocutaneous perforators supplied the
skin over the medial calf. We noted that perforators of the medial sural artery were
consistently arranged in two vertical rows (a medial and a lateral row) along the
axis of the leg. By dividing the medial gastrocnemius bulk into equal thirds vertically,
the lines between adjacent thirds serve as approximate surface landmarks for the medial
and lateral rows of perforators ([Fig. 1]). Perforators were more plentiful and larger in the lateral row, which was situated
closer to the posterior midline of the leg, ~2 cm away ([Fig. 2]). Large perforators were identified in the medial row (~6 cm medial to the posterior
midline) in only five of the ten lower limbs.
Figure 1 The medial sural artery divides into two branches and perforators are given off along
each of their lengths. The perforators are orientated in two parallel rows, which
can be landmarked by roughly dividing the gastrocnemius muscle bulk into thirds.
Figure 2 They are clustered ~2 cm (lateral row) and 6 cm from the posterior midline (medial
row). The proximal perforators are clustered an average of 10 cm from the popliteal
crease, whereas the distal group of perforators lie an average of 15 cm from the popliteal
crease.
In nine out of ten specimens, a consistent large perforator could be identified between
10 cm (±2 cm) from the popliteal crease and an average 2 cm (±0.5 cm) from the posterior
midline. This reliable perforator had a superficial axial intramuscular course when
traced to its origin from the lateral branch of the medial sural artery ([Fig. 3]). In one specimen, this perforator was located more distally, 15 cm from the popliteal
crease. A second perforator was found in the medial row at 10 cm distal to the popliteal
crease.
Figure 3 In nine of ten specimens, a consistent major perforator could be identified between
10 cm (+/−2 cm) from the popliteal crease and an average 2 cm (+/−0.5cm) from the
posterior midline. This perforator was large and had a superficial intramuscular course,
facilitating intramuscular dissection.
Most perforators appeared to arise in the proximal half of the medial gastrocnemius
muscle bulk; although in half the leg specimens, at least one other reliable perforator
could be identified 16 cm (±2 cm) from the popliteal crease ([Fig. 4]). Pedicle length of 11 to 19 cm (mean = 13.7 cm) could be obtained at completion
of flap harvest. The mean diameter of the major perforators at the subfascial level
ranged from 1 to 2 mm (mean = 1.5 mm). The medial sural artery itself averaged 2.5
to 3 mm in diameter.
Figure 4 Distribution of major perforators (>1.0 mm) Perforators in the lateral row (nearer
the posterior midline of the leg) are more dominant.
Based on this information, we modified our surgical approach to harvesting the medial
sural artery perforator flap. Preoperatively, the medial calf was examined with the
handheld Doppler. The preferred perforator was the one located ~10 cm from the popliteal
crease and 2 cm from the midline. The flap was harvested with no tourniquet applied
to enable observation of pulsation of the perforator prior to committing to its use
as the vessel nourishing the flap. The lateral (nearer to the posterior midline) incision
was made first, as this enabled the surgeon to get to the medial row where the location
of the dominant perforator was most likely located. Having identified the perforator,
the skin was completely islanded and intramuscular dissection completed to elevate
the flap. The pedicle was mobilized to the origin of the medial sural artery from
the popliteal artery, usually located at the level of the popliteal crease. Using
this approach, we successfully used this flap in five clinical cases. The mean pedicle
length was 12 cm (range = 9 to 15 cm). All flaps were successfully raised and survived
uneventfully. In three cases, the donor site required skin grafting. In two cases
where a small flap was harvested, the donor site could be closed primarily.
Case 1
A 19-year-old female presented with a right dorsal hand defect after debridement of
an abscess secondary to extravasation injury ([Fig. 5a]). The 3 cm by 5 cm defect with exposed extensor tendons was covered with a contralateral
medial sural artery perforator flap. Preoperative examination with the handheld Doppler
showed that the perforators were located in two rows, as expected from our cadaveric
study ([Fig. 5b]). A posterior midline incision was made first, and dissection proceeded subfascially.
Intraoperatively, the medial sural artery divided into two branches 2 cm from its
origin from the popliteal artery. Correspondingly, one perforator could be identified
in the medial row (10 cm from popliteal crease and 5 cm from the posterior midline),
arising from the medial branch. Another more substantial perforator (10 cm from popliteal
crease and 2 cm from the posterior midline) arose from the lateral branch of the medial
sural artery. Both perforators were completely unroofed, and the flap was islanded
and raised based on both branches of the medial sural artery ([Fig. 5c]). End-to-end anastomoses were performed between the medial sural artery and one
vena comitans to the princeps pollicis artery and a dorsal cutaneous vein respectively.
One side of the flap was left unsutured due to intraoperative swelling, and secondary
suture was completed 4 days later. The donor site was skin-grafted. Healing was uneventful.
Secondary debulking of the flap was performed with good results ([Fig. 5d], [5e]).
Figure 5 (a) A 19-year-old female presented with a right dorsal hand defect with exposed extensor
tendons. (b) A left medial sural artery perforator flap was designed and the perforators
were localized preoperatively. (c) The flap was harvested based on two perforators,
one arising from each branch of the medial sural artery. The more substantial perforator
arose from the lateral branch of the medial sural artery. (d, e) Final result shows
acceptable contour and excellent hand function
Case 2
A 22-year-old male smoker presented with a left foot degloving injury exposing the
first metartarsophalangeal joint. The defect measured 7 cm by 6 cm ([Fig. 6a]). The patient was positioned prone, and dissection proceeded from a posterior midline
incision. An ipsilateral medial sural artery perforator flap was harvested based on
a large lateral row perforator (8 cm from popliteal crease and 2 cm medial to posterior
midline) arising from the lateral branch of medial sural artery ([Fig. 6b]). The patient was turned back supine and end-to-end anastomoses were performed between
the medial sural artery pedicle to the dorsalis pedis artery, one accompanying vena
comitans and a branch of the great saphenous vein. The donor site was covered with
an unmeshed split-thickness skin graft ([Fig. 6c]). Secondary flap debulking was performed 6 months later with good final contour
of the flap ([Fig. 6d], [6e]).
Figure 6 (a) A 22-year-old male presented with a left foot degloving injury with exposure
of the first metatarsophalangeal joint. (b) An ipsilateral medial sural artery perforator
flap was harvested based on a large lateral row perforator (8 cm from popliteal crease
and 2 cm medial to posterior midline) arising from the lateral branch of the medial
sural artery. (c) Appearance of the donor site after skin-grafting. (d, e) Good final
contour of the flap after secondary debulking.
Discussion
Since its description in 2001 by Hallock[13] and, independently, by Cavadas,[3] the medial sural artery perforator flap has been shown to be a promising flap for
coverage of regional and distant defects. It is muscle sparing with limited donor
morbidity; because of intramuscular dissection, its pedicle length and arc of rotation
are superior to the conventional medial gastrocnemius myocutaneous flap.[5] It has found applications as a pedicled flap for defects of the knee and upper third
of the lower leg[4]
[5] and as a free flap for head and neck and limb reconstruction.[6]
[7]
[8]
[9]
[10]
[11]
[14] Inclusion of the plantaris tendon, sural nerve, and gastrocnemius muscle increases
its versatility as a chimeric flap.[15]
[16]
Despite its advantages, concerns limiting its use include the variability of its vascular
anatomy and the need for intramuscular dissection.[17] Cavadas[3] first reported that the perforating vessels were clustered 8.5 to 19 cm from the
popliteal crease. In the most frequent case when two perforators were present, Thione
et al[18] concluded that the proximal one was at an average distance of 10.7 cm (range = 8
to 13 cm) from the popliteal crease, and the distant one was at an average distance
of 16.3 cm (range =12.5 to 18 cm). In comparison, studies on Asian populations postulated
that the perforators were located 1 to 2 cm more proximally due to either shorter
leg length[19] or skin folding with flap harvest in knee flexion.[20]
Consistent with previous studies,[3]
[18]
[19]
[20]
[21] we found the proximal and distal perforators to be located at an average of 10 cm
and 16 cm from the popliteal crease. Although the vertical distances are quite well
described, their locations in the horizontal plane with respect to the posterior midline
remains conflicting and poorly defined.[20]
[22] We found that the medial sural artery divides into two branches[14] shortly after it pierces the medial gastrocnemius muscle: a medial and a lateral
branch. These two branches traverse vertically down the muscle and give off musculocutaneous
perforators, which are thus arranged in two parallel rows ~2 cm and 6 cm, respectively,
from the posterior midline of the leg. The lateral row perforators are commonly larger
and more dominant. In none of the specimens was the medial system dominant. In all
except one leg, the most consistent major perforator was found ~10 cm from the popliteal
crease and 2 cm from the posterior midline. This reliable perforator had a superficial
straight intramuscular course, just beneath the surface of the muscle, thus facilitating
intramuscular dissection. Computed tomography (CT) angiography may be useful in confirming
the presence of this perforator[23]; however, it may not always be available. Therefore, to successfully identify and
preserve this largest perforator early on in the dissection, we propose that the initial
incision when raising the flap should start from the posterior midline. Once it is
located, the surgeon must visually confirm that the perforator is pulsating well.
Sometimes the supposed “perforator” may in fact be a cutaneous nerve that does not
carry an artery. The flap can then be completely islanded and the intramuscular dissection
completed in the usual manner using perforator flap techniques.[24]
When a second perforator is found in the distal half of the medial gastrocnemius,
this is typically smaller than the proximal perforator but may still be chosen to
provide an increased arc of flap rotation in the appropriate clinical situation.
