Keywords
medial sural artery perforator free flap - microvascular surgery - lower extremity
- foot and ankle
The possibility of use of the integument of the medial calf as a free flap donor site
based on musculocutaneous branches of the medial sural vessels was first investigated
in cadaver dissections by Taylor and Daniel.[1] Montegut and Allen[2] presented this at a regional meeting as a local flap alternative to the gastrocnemius
myocutaneous flap. At the 5th International Course on Perforator Flaps in Gent, Belgium
(2001), the anatomical basis of the requisite perforators to the medial sural artery
flap was given as a free paper,[3] immediately followed by Cavadas et al explaining their clinical series in using
this as a free flap.[4] Since then, these original anatomical findings have been verified,[5]
[6]
[7]
[8] and clinical applications as a thin perforator flap have run the gamut throughout
the body proving versatility in the head and neck[9]
[10] to the distal extremities,[5]
[9]
[11]
[12]
[13]
[14] indeed head-to-toe. In a podium discussion at the session for use of perforator
flaps for the lower extremity at the 6th Conference of the World Society for Reconstructive
Microsurgery in Helsinki, Finland (2011),[15] many observers on the contrary took exception and vociferously opposed use of this
donor site for any part of the body without exception; as the disfigurement at the
donor site even if closed primarily to leave just a linear scar on the calf, much
less if skin grafted, was generally unacceptable but even more so as an aesthetic
defect for women. It was pointed out that a superficial circumflex iliac perforator
flap[16] or medial circumflex femoral artery perforator flap[17] could achieve the same purpose, while leaving a defect in the lateral or medial
groin, respectively, which could easily be hidden by normal clothing. This moderator
suggested a counterargument in that if used for the ipsilateral distal lower extremity
where there would ultimately be an aesthetic deformity at the defect site anyway,
the attributes of this flap could outweigh this disadvantage.[15] Therefore, for this specific indication, consideration of the use of the medial
sural artery perforator (MSAP) flap as a free flap would be legitimate, as to be discussed
here in more detail.
Methods and Materials
A retrospective review of our free flap registry over the past decade found 14 patients
with distal lower extremity wounds who had had a perforator flap using the cutaneous
territory of the ipsilateral medial sural artery ([Table 1]). Only two (14%) were females. In all cases but one, the defect requiring coverage
was a sequel of some form of trauma, and essentially these involved all zones of the
foot and ankle ([Fig. 1]) where a thin flap was essential to permit use of everyday shoe wear.
Fig. 1 Zones of the distal lower extremity including foot and ankle.[22] Zone 1, distal foot and toes; zone 2, plantar forefoot; zone 3, dorsal foot; zone
4, midfoot; zone 5, hind foot; and zone 6, distal leg and ankle.
Table 1
Medial sural artery perforator flap characteristics
|
Name
|
Etiology
|
Location defect[a]
|
Size (cm)
|
Perforators
|
Donor site
|
Recipient vessels
|
Complications
|
|
JA
|
MCA—heel degloving
|
5
|
5 × 8
|
1
|
Scar
|
PT
|
|
|
AB
|
Fall: fibula fx
|
6
|
3 × 10
|
2
|
Scar
|
AT
|
|
|
BC
|
Crush—great toe amp
|
1
|
6 × 17
|
1
|
Skin graft
|
DP
|
|
|
JE
|
Fall: distal tibia fx
|
6
|
5 × 15
|
3
|
Skin graft
|
PT
|
Chimeric; patient died
|
|
JF
|
Fall: pylon fx
|
6
|
3 × 7
|
1
|
Scar
|
PT
|
|
|
DK
|
Fall: calcaneal fx
|
5
|
5.5 × 10
|
2
|
Skin graft
|
AT
|
Venous congestion; 2nd free flap salvage
|
|
MM
|
Fall: achilles avulsion fx
|
5
|
4.5 × 12
|
1
|
Scar
|
PT
|
Dehiscence donor site closure
|
|
SN
|
Fall: pylon fx
|
6
|
3 × 5
|
1
|
Scar
|
PT
|
|
|
EO
|
Club foot— unstable scar
|
5
|
6 × 11
|
1
|
Skin graft
|
PT
|
|
|
RS
|
Fall: calcaneal fx
|
5
|
4 × 11
|
2
|
Scar
|
AT
|
|
|
AS
|
Fall: calcaneal fx
|
5
|
3 × 8
|
2
|
Scar
|
AT
|
|
|
GV
|
Fall: distal tibial fx
|
6
|
3 × 7
|
2
|
Skin graft
|
PT
|
|
|
JW
|
ATV: great toe avulsion
|
1/3
|
4 × 13
|
1
|
Scar
|
DP
|
Lateral sural perforator anomaly
|
|
RW
|
Fall: distal fibula fx
|
6
|
3 × 11
|
2
|
Scar
|
AT
|
|
Abbreviations: AT, anterior tibial; ATV, all-terrain vehicle accident; fx, fracture;
DP, dorsalis pedis; MCA, motor cycle accident; PT, posterior tibial.
a Zone of distal lower leg or foot ([Fig. 1]).
Surgical Technique
Preoperative planning first requires identification of a desirable perforator of the
posterior calf overlying the medial gastrocnemius muscle. Wang et al[5] suggest that a perforator will be found within a circle of radius 4 cm that is centered
at the intersection of a line drawn from the medial epicondyle of the femur and prominence
of the lateral malleolus, and a second line drawn from the midpoint of the popliteal
crease to the medial malleolus, which thereby will take into account variability in
height of the individual. The latter line roughly corresponds to the course of the
medial sural artery, and according to Kim et al,[6] a second perforator may sometimes be found within 7 cm distal to the first. Unfortunately,
these are only rough guidelines as variation here is common[18]; and, unless computed tomography angiography or color duplex ultrasound[7] is available, the ubiquitous handheld acoustic Doppler by default may be a reasonable
substitute for widely scanning this region[19] for a perforator of choice.
A template of the defect should be eccentrically placed with about two-thirds of the
design distal to the chosen perforator to allow a longer pedicle, if needed. The major
axis of the design should parallel the tibial border to best capture adjacent perforasomes
if a longer flap is needed.[20] The entire procedure can be performed within a bloodless field by using a tourniquet,
but without previous exsanguination to ensure that venous structures remain filled
and highly visible. Note that calf perforators tend to course obliquely for some distance
after leaving the heads of the gastrocnemius before piercing the deep fascia, presumably
to safely adjust for muscle contraction during ambulation. Therefore, after incising
only the anterior border of the MSAP flap through the subcutaneous tissues, a subfacial
dissection may be the safest approach to first confirm the exact location of the perforator.
Often, the actual site of facial perforation is different than suspected, so the design
must be correspondingly altered. Next, the usual tedious intramuscular dissection
of these relatively diminutive perforators back to a branch of the medial sural vessels
must be completed until the desired pedicle length and/or vessel caliber is obtained.
Any motor nerves encountered are carefully protected. The posterior boundary can then
be incised through the deep fascia to create an island flap. At the superior flap
margin, a large subcutaneous vein, if encountered, should be kept to permit flap venous
supercharging later if needed, although this maneuver is rarely required. The tourniquet
is next deflated and flap perfusion assessed. If adequate, transfer to the recipient
defect with the requisite microanastomosis is performed per routine. Donor site closure
requires a skin graft if primary closure is too tight to avoid an iatrogenic compartment
syndrome.[21]
Results
All MSAP flaps in this series were for ipsilateral traumatic defects except for one
unstable surgical scar ([Table 1]), with the majority (86%) involving men. Most were used for the distal leg and ankle
or hind foot zones according to the Duke classification ([Fig. 1]).[22] One patient had a chimeric flap including a portion of the medial gastrocnemius
muscle for fill of a bony defect.[23]
[24] The flap lived, but the patient succumbed from congestive heart failure in the immediate
postoperative period. One flap was lost in a diabetic patient with a calcaneal fracture,
secondary to venous congestion, which had to be salvaged with a different free flap,
for an overall success rate of 92.9%.
A single perforator was utilized in 7/14 (50%) of flaps, with more only if they lined
up along the same medial sural branch during the dissection of the flap pedicle, and
if each seemed particularly diminutive. The largest flap was 17 cm in length and well
served by a single perforator. In one case, the only perforator found over the medial
head of the gastrocnemius muscle actually crossed the midline and emanated from the
lateral head, so technically this was a lateral sural artery perforator flap. Lateral
ankle and foot, plus some Achilles defects required the anterior tibial vessels as
the recipient site. Some Achilles and all medial ankle defects used the closer posterior
tibial vessels. Forefoot or toe defects used the dorsalis pedis artery and a subcutaneous
vein as the recipient vessels. Regardless of the recipient artery, in all cases an
end-to-side anastomosis was performed, with end-to-end venous anastomoses.
A skin graft was necessary for 5/14 (36%) of the donor sites, and usually only if
flap width were greater than 5 cm, although in one obese male a 3 cm wide flap required
a skin graft so as to avoid excessive tension during skin approximation. A linear
scar was left for both female patients.
Case Example: Zone 5—Posterior Hind Foot
Patient MM lost his balance while cleaning his truck and sustained a closed left Achilles
tendon avulsion fracture. Reinsertion was performed by suturing the tendon to screw
anchors in his comminuted calcaneus. The surgical wound never healed and became infected,
requiring that all foreign material be removed some 6 months after the accident. During
this same time period he had been treated at a local wound center with no progress.
The Achilles tendon remained exposed ([Fig. 2]), but there was by this time no evidence of osteomyelitis. Therefore, a 4.5 cm × 12
cm MSAP free flap from the ipsilateral calf was raised based on a single perforator.
The posterior tibial vessels were the recipient site. The primary donor site closure
dehisced slightly, but healed with conservative treatment only. He returned to work
2 months later fitting easily into his normal steel-tipped reinforced work boots without
further difficulty.
Fig. 2 Patient MM. (A) Exposed left Achilles tendon, (B) original median sural artery perforator
(MSAP) flap design (solid line) on ipsilateral medial calf about perforator “x” heard
with audible Doppler, but following anterior exploratory incision with exact perforator
identification, was moved slightly distally (dotted line), (C) island MSAP flap in
situ with microgrid under vascular pedicle in trough created by division of medial
gastrocnemius muscle fibers, showing how superficial the vascular supply can be, (D)
the free MSAP flap based on a single perforator, (E) healed heel with widened donor
site scar of ipsilateral calf.
Case Example: Zone 6—Distal Leg and Ankle
Patient AB fell down her basement steps sustaining a closed bimalleolar left ankle
fracture. The lateral ankle incision used for plate fixation of her fibula never really
healed, with hardware exposure occurring 11 weeks after this surgery ([Fig. 3]). The plate was removed leaving the fibula exposed. Local tissues were extremely
indurated and unsuitable to be used for bony coverage. For this narrow wound, a gracilis
muscle free flap was considered. Instead, a 3 cm × 10 cm MSAP free flap from the ipsilateral
calf was raised based on 2 perforators that serendipitously entered opposite ends
of the flap to insure complete flap perfusion. The anterior tibial vessels were the
recipient site. The donor site could be closed primarily. After 2 months, the appearance
of the left lower leg was superior to a skin grafted muscle free flap.
Fig. 3 Patient AB. (A) Exposed left fibula fracture fixation plate, (B) following plate
removal, bone remains exposed. Note nearby anterior tibial recipient site. (C) Flap
designed longitudinally about perforator “x” heard with audible Doppler, that was
found along line drawn from midpoint of the popliteal crease to the prominence of
the medial malleolus, (D) free medial sural artery perforator (MSAP) flap with two
perforators emanating from the same branch of the medial sural vessels fortuitously
at opposite ends of the flap, (E) healed MSAP flap 2 months later, (F) linear scar
of medial calf donor site.
Discussion
The MSAP flap usually relies on musculocutaneous perforators of the medial head of
the gastrocnemius muscle; and the existence of at least one of adequate size is normally
present,[3]
[7]
[8] although none were found in one case in this series, albeit an alternative was nearby.
Pedicle caliber is sufficient for patulous microanastomoses, with the artery up to
2 mm and vein 4 mm in diameter.[13] Pedicle length in our anatomical dissections had a mean of 15.3 cm,[3] and clinically can easily exceed 10 cm[9]
[13] to allow reach to a recipient site well above the ankle ([Fig. 3]); so as to avoid the need for vein grafts and yet still be outside the zone of injury
of a given foot defect. This characteristic also avoids sacrifice of a major artery
to the foot, where often circulation already is compromised. The MSAP flap is relatively
thin even in the obese individual,[25] which is important for foot and ankle defects where motion during ambulation and
use of shoe wear cannot be impeded. Flap harvest can be done with the patient in either
a supine or prone position.[25] A tourniquet may be used to create a bloodless field to facilitate dissection. The
course of perforators from the medial sural branches tend to run longitudinally very
close to the posterior surface of the muscle[3] ([Fig. 2]), so that pedicle dissection is simplified compared with other major perforator
flap donor sites. Spinal anesthesia alone may be satisfactory for patients with other
comorbidities. Chimeric flaps including vascularized plantaris tendon or gastrocnemius
muscle can simultaneously be transferred independently.[23] Of course, as with all perforator flaps, there is minimal muscle damage so that
function is maximally preserved.
The MSAP perforators are relatively diminutive so that great care must be observed
during their dissection, but this should not be beyond the ability of the usual microsurgeon.
However, the other major disadvantage may be an insurmountable obstacle. That is the
residue left at the donor site. Even a linear scar, much less a skin graft, is understandably
highly objectionable especially for women, as this is not easily hidden by clothing.
When the MSAP flap is chosen for head and neck or upper extremity problems, this would
then be inappropriate as long as other better alternatives are available.[16]
[17] Yet one could legitimately argue that for the ipsilateral lower extremity where
a thin free flap is necessary that can be easily and rapidly harvested, that a MSAP
flap is a reasonable alternative. All dissection is within the same field. All eventual
residue will be close together, so that the scarring inevitable and obvious at the
recipient site may be little different or perhaps worse than that of the MSAP calf
donor site itself. Even in a woman, an adjacent linear scar may be better than having
another body region violated. That decision must be understood and approved by the
patient before embarking on whatever course is needed to provide lower limb salvage. The MSAP flap
provides here another justifiable alternative.
