Keywords
fibula - free tissue flaps - tibial arteries - lower extremity - foot
The free fibula flap (FFF) has become one of the workhorse flaps since its introduction
by Taylor et al in 1975.[1] It has been widely used to reconstruct posttraumatic and postoncological resection
bony defect due to its versatility, ease of harvesting, and long vascular pedicle.[2] Hidalgo further developed this flap for mandibular reconstruction in 1989 as it
has a thin and pliable bone, as well as the presence of cutaneous island allowing
reconstruction of both mandible and the surrounding soft tissues.[3]
The FFF is based on the peroneal artery (PA), and it is well known that several anatomical
variations of the lower limb vascular system exist. PA usually arise from the posterior
tibialis artery (PTA) 2.5 to 3 cm below the lower border of the popliteus muscle,
and subsequently branches off to give rise to peroneal nutrient arteries, periosteal
branches, and septocutaneous arteries to the skin over the lateral aspect of the leg.[2] The variations of the origin, course, and diameter of the anterior tibialis artery
(ATA), PTA, and PA were initially described and classified by Lippert and Pabst in
1985[4] and later modified by Kim et al in 1989.[5] The Kim-Lippert's Classification has now become the widely used guide to describe
the infrapopliteal arterial branching variations.[5]
The knowledge of the third group in Kim-Lippert's Classification is of the utmost
importance in the harvest of FFF because it describes the presence of hypoplasia or
aplasia of the tibial arteries with the PA being the dominant artery supplying the
peripheral pedal arterial supply via dorsalis pedis artery (DPA) and PTA. In Class
III C, both ATA and PTA are either hypoplastic or aplastic: otherwise commonly known
as peronea arteria magna (PAM).[5]
[6] The prevalence of PAM is estimated at only 0.4%. Albeit scarce, the awareness of
its existence is crucial as it often precludes FFF from being harvested due to the
risk of significant limb ischemia and limb loss.[6]
We present a case with an incidental intraoperative finding of PAM that had a successful
FFF harvest by luck, without preoperative vascular mapping.
Case Report
Ms. A is a 17-year-old female with no known comorbidity, presented in August 2020
with a 1-year history of swelling and tenderness over her left foot. A magnetic resonance
imaging (MRI) was performed in a private center, which showed an enhancing well-circumscribed
mass centered in the second webspace (between second and third metatarsal shafts)
involving interosseous muscles, most likely soft tissue tumor or sarcoma. Resection
was done; however, the histopathology examination (HPE) report came back as perineuroma
with the surgical margins' involvement. Unfortunately, the swelling recurred 8 months
postoperatively. She was then referred to our center for further management. Our clinical
examination revealed a well-healed scar with an ill-defined swelling over the dorsum
of her left foot. A repeat MRI showed a lesion surrounding the second metatarsal with
local infiltration to the overlying muscles and bone of the second and third metatarsal,
suggesting tumor recurrence.
She underwent wide resection of left foot tumor, left extensor digitorum tendon repair
with peroneal brevis tendon graft, and left foot reconstruction with a free fibular
osteocutaneous flap. The tumor encased the left second and third metatarsal bones;
hence these bones and overlying second and third extensor digitorum longus tendons
were removed together. The resulting soft tissue and bony defect measured approximately
8 × 8 × 4 cm ([Fig. 1A]). The harvested fibular bone was osteotomized, and 8 cm of bone and its skin paddle
were used to bridge the bony defect; proximally to middle and lateral cuneiform and
distally to second and third proximal phalanges. The arterial anastomosis was performed
between the flap's PA and recipient site's DPA, while the venous anastomosis between
the respective vena comitans of each artery. The flap was secured in place with a
T plate and screws post-anastomosis. The wound was then covered with the skin paddle
([Fig. 1B]). The configuration of the reconstruction is portrayed in the X-ray ([Fig. 1C]).
Fig. 1 The reconstruction with free fibula osteocutaneous flap. The patient's left foot
was reconstructed with a free fibula flap following oncological resection of the tumor.
(A) The defect after tumor resection, measuring 8 × 8 × 4 cm. (B) The immediate postoperative flap appearance. (C) The flap's osseous configuration as shown in an X-ray.
During the flap's harvest on the contralateral leg, a large dominant PA emerged from
the popliteal artery supplying the flap and providing a dominant blood supply to the
foot. Further exploration also revealed aplastic PTA and hypoplastic ATA originating
from the popliteal artery. The PA is shown by white arrowhead, while the black arrow
demonstrates the aplastic PTA ([Fig. 2A]). The aplastic PTA was seen tapering down and abruptly terminated at the level of
the mid tibia. The hypoplastic ATA was small in caliber upon exploration and slightly
expanded upon distal PA ligation (marked by the red arrow in [Fig. 2B]). These findings correspond to the type III-C in Kim-Lippert's Classification. Preoperatively,
clinical examination revealed normal DPA and PTA pulses, and flap planning was performed
with a handheld Doppler in the usual manner. However, no preoperative angiography
was performed to reconfirm the donor leg vascularity.
Fig. 2 The finding of peronea arteria magna (PAM) intraoperatively. Clinical findings of
PAM upon flap harvest and elevation. (A) The prominent peroneal artery (PA) with extensive branching is shown by the white
arrowhead, while the black arrow demonstrates the very small aplastic posterior tibial
artery (PTA), which was seen tapering down and abruptly terminated at the level of
mid to distal tibia. (B) The small caliber hypoplastic anterior tibialis artery (ATA) is marked by the red
arrow and has become slightly expanded upon distal PA ligation.
Additional precautionary steps were taken during harvest to avoid any ischemic event
to the right lower limb. The tourniquet was first released, and the PA was clamped
before it was divided. Distal circulation assessment and monitoring of the right foot
were performed during clamping. After 15 minutes of clamping, the right DPA remained
palpable clinically and was detectable by handheld Doppler. The oxygen saturation
over the right lower limb distal extremity was also maintaining at 100%, demonstrating
adequate residual blood flow to the foot. The artery was then divided, and the flap
was raised without any acute or chronic ischemic complications. HPE came back as deep
(desmoid type) fibromatosis, with all margins' involvement except the superficial
and proximal margins. She was then subjected to adjuvant radiotherapy.
Six months postoperatively, no ischemic event or right leg claudication was reported.
The right leg donor site healed well, and no noticeable skin changes suggestive of
an ischemic limb were observed ([Fig. 3A]). The flap also remained viable with no tumor recurrence ([Fig. 3B]), and the patient could fully bear weight. There was a solid bony union with increased
radiodensity suggesting bone remodeling and graft viability, as shown in the foot
X-ray ([Fig. 3C]). A more extended follow-up period is warranted for her. Although there was no necrosis
of the distal foot area suggesting an acute ischemic event, chronic hypoperfusion
may cause delayed manifestation of soft tissue, muscle, and bone atrophy.
Fig. 3 Right leg (donor site) and left foot (recipient site) appearance after 6 months.
The observations as shown by clinical and radiological examinations. (A) The donor site healed well with no obvious skin changes suggestive of ischemic limb.
(B) The flap appearance after 6 months. (C) Left foot's X-ray showing minimal hypertrophy with no resorption suggesting graft
viability.
Discussion
PAM is a rare congenital variation in which the ATA and PTA are either absent or hypoplastic,
and as a result, PA will be the dominant blood supply to the foot.[5] Limb ischemia and limb loss are often the feared adverse complications from the
FFF harvest in these patients.[6] Albeit some literature reporting donor site complications and impending limb loss
following FFF harvest in PAM, preoperative vascular mapping before FFF transfer remains
controversial among the microsurgeons.[7]
[8]
[9] For instance, Rosson and Singh in 2005 reported an unsuccessful FFF harvest in a
patient with PAM, requiring an emergency vascular bypass with a reversed saphenous
vein graft to regain limb perfusion.[10] It was also reported that the cost-to-benefit ratio and some imaging modalities'
invasiveness contribute to this ongoing debate.[10]
Several authors advocate for preoperative vascular mapping of the FFF donor leg by
using the computer tomography angiography (CTA), digital subtraction angiography (DSA),[9] and magnetic resonance angiography (MRA).[8]
[11] CTA may be the preferred initial screening tool for detecting vascular pathologies.
For equivocal findings, DSA is deemed superior to CTA in terms of contrast and spatial
resolution. The invasiveness of DSA carries undesirable risks such as internal bleeding,
arterial puncture, thrombosis, infection, vessel dissection, pseudoaneurysm, hematoma,
and renal injury to the contrast medium.[8] MRA offers an alternative option as it is not invasive and can give excellent visualization
of the leg vascular anatomy.[10]
[12] Nevertheless, MRA is costly, and metal fixators or implants are contraindicated
for its usage.[8]
On the other hand, some authors oppose the use of preoperative imaging of the donor
limb[7]
[13] as it is believed that preoperative clinical examination and intraoperative assessment
are reliable enough without the need for additional preoperative imaging. They also
believe that the FFF harvest can be abandoned if PAM is identified intraoperatively;
however, the added cost from the additional surgery and morbidity must be considered.
It is worth noting that PAM can even be present in patients with a normal clinical
vascular examination. Both DPA and PTA may be palpable due to the collateral branches
of the dominant PA supplying these vessels.[10] In a study by Young et al, two of their participants had PAM despite normal distal
pulses during the clinical examination.[14]
In PAM (subtype III-C), the PA is the only dominant vessel supplying the foot; hence
its removal during the FFF harvest may result in limb ischemia or total limb loss.
In the other two subtypes, the larger diameter dominant PA shares the blood supply
to the foot either with the ATA or PTA, while the other tibial vessel counterpart
being hypoplastic. These variations are not easily detected by clinical examination
alone without preoperative vascular imaging, unlike Allen's test used in the forearm
to detect radial or ulnar arteries dominance.[6]
Despite being one of the main referral centers in Malaysia for major reconstruction,
we do not perform routine preoperative imaging to assess FFF donor limb, except in
patients with a significant previous history of trauma or other comorbidities that
may compromise vascularity the fibula flap's donor site. In such cases, we usually
opt for the more conventional CTA. Our practice is due to the high cost-to-benefit
ratio owing to PAM's rarity in our population. In the last 5 years (from 2016 to 2020),
we have performed 51 free fibular transfers for various etiologies and only one of
these patients presented with PAM. Unnecessary routine imaging will add a substantial
strain to our busy and overburdened radiology unit. Only clinical assessment, perforator
identification, and flap planning with handheld Doppler were made in most cases, including
this case.
Due to limited options for simultaneous bone and cutaneous reconstruction and to avoid
unnecessary morbidity and cost increase due to aborted procedure, the FFF was still
harvested with strict precaution and rigorous postoperative monitoring despite the
relative contraindication in PAM. It is worth noting that despite our practice, we
do advocate the use of preoperative imaging to avoid any donor's ischemic complications
posttransfer. However, we are unable to routinely use preoperative vascular mapping
as a standard due to the limitations described above.
The increase in blood flow through the hypoplastic ATA and collateral vessels may
have provided adequate residual blood flow to the right foot following the distal
PA's ligation. Unfortunately, the evidence is limited as this was not explored postoperatively
with further imaging due to logistic issues caused by the COVID-19 pandemic. This
case provides some evidence that with meticulous techniques, care, and a bit of luck,
FFF may be safely harvested from a patient with PAM. Nevertheless, this practice is
risky, requiring rigorous postoperative care and a low threshold for an emergency
vascular bypass for limb salvage. We still believe that in an ideal situation with
unlimited resources, preoperative imaging is mandatory to prevent unnecessary donor
limb morbidity or even limb loss.
