Keywords
ankle - perforator flap - wound healing
Introduction
Trauma, tumor, diabetes mellitus, and peripheral vascular disease are responsible
for majority of cases that present with soft tissue defect of lateral ankle.[1]
[2] Defects related to diabetes mellitus especially presents a significant challenge
in terms of reconstruction and healing.[3] In culture where sitting cross-legged on the floor is common, the lateral ankle
wound becomes further difficult as they are usually presented with a large dead space,
small skin opening that often accompanies an open joint.
The first line for reconstruction can be a simple rotation of a local flap or a propeller
flap based on peroneal artery perforator.[4] These fasciocutaneous flaps are commonly utilized and have provided several advantages
in lateral ankle reconstruction including reduced operative time and improved wound
healing. However, the use of fasciocutaneous local flaps or propeller flaps, in which
a skin paddle is harvested from a tight donor site often can lead to morbidity such
as delayed wound healing or nerve injury.
To address these issues for diabetes-related lateral ankle defects where the dead
space is far greater issue than the skin defect, the authors aimed for a flap that
can obliterate the dead space while allowing smooth gliding for underneath structures.
Theoretically, obliterating the dead space with fat can be anatomically ideal. Thus,
the adiposal layer only flap or so called the pure fat flap based on a single perforator
was designed. The pure fat flap will preserve the subdermal plexus of the skin allowing
the donor site skin to heal without the need for any skin grafts, preserve the deep
fascia reducing the chance of muscle hernia or nerve injury. To our knowledge, this
is the first case of utilizing a pure fat flap of moderate size which was performed
to obliterate the dead space and provide coverage for the lateral ankle defect.
Case
A 46-year-old male patient was noted with bursitis of the left lateral malleolus.
The orthopaedic team performed multiple incisions and drainage without success and
ultimately referred to reconstruction for the defect. Debridement was performed and
resulted in a 2.5 × 2 cm skin defect and a 5 × 5 cm dead space pocket with small opening
of the joint leaking fluid ([Fig. 1A]). A contrast-enhanced magnetic resonance imaging of the left ankle was performed,
revealing no evidence of osteomyelitis. The patient had history of coronary intervention
for 3-vessel disease, end-stage renal disease on hemodialysis, and had diabetes for
20 years. The ankle brachial index was 1.35 on the left side (1.28 on the right side),
and enhanced computed tomography lower extremity angiography revealed patency of the
anterior tibial artery, posterior tibial artery, and peroneal artery, which was further
confirmed by ultrasound examination. Prior to coverage, duplex ultrasonography was
used preoperatively to find a perforator that would allow a perforator-based adiposal
layer turnover flap ([Fig. 1B]).[5] A perforator was identified from the peroneal artery.
Fig. 1 (A) (Left) Preoperative photo of patient 1. (Right) Postoperative photo of patient 1
after debridement. (B) Ultrasonographic finding of patient 1, showing peroneal artery (shown by arrowheads)
and accompanying perforator from peroneal artery (shown by arrow). It was traced before
surgery using color duplex ultrasound. (C) Adiposal layer only flap design of patient 1 according to perforator course. (D) (Above, Left) After adiposal layer only flap elevation. (Above, Right) After flap
rotation. (Below, Left) ICG video angiography after flap rotation. Note that flap
is well perfused including distal portion after rotation. (Below, Right) Immediate
postoperative photo. (E) Postoperative ultrasonographic finding showing intact pedicle. Peroneal artery perforator
is seen (shown by arrow) and continued in axial pattern (shown by arrowheads). (F) Postoperative 8 months photo of patient 1. ICG, indocyanine green.
A 9 × 4 cm turnover pure fat flap was designed based on the perforator located 2 cm
from the edge of the defect ([Fig. 1C]). Dissection was performed above the deep fascia, perforator was identified, and
adiposal layer only flap was elevated preserving subdermal plexus. The sural nerve
was also saved. The perforator based pure fat flap was elevated and turned over to
cover lateral malleolus. The indocyanine green angiography confirmed the flap perfusion.
Primary closure with quilting suture was performed at the donor site to eliminate
dead space. The pure fat flap obliterated and covered the defect, and the skin was
closed primarily. A silastic drain was placed at the lateral ankle with a splint to
immobilize the joint ([Fig. 1D]).
Postoperative process was uneventful, and the drain was removed on day 4. The follow-up
duplex ultrasound on day 5 showed good flow ([Fig. 1E]). The follow-up at 8 months showed good coverage and healing with minimal donor
site morbidity ([Fig. 1F]).
Discussion
For diabetes-related lateral ankle defects with specific features such as dead space
and a relatively small skin defect, several factors need to be considered. The presence
of dead space in the lateral ankle defect refers to the gap or void that may exist
above the lateral malleolus, which is easily seen during debridement for wound preparation.
Dead space can pose a challenge to wound healing and increase the risk of complications
such as fluid accumulation and infection. It is, therefore, critical to effectively
manage this dead space to promote optimal healing and functional outcomes. The dynamic
nature of the ankle also requires the provision of a gliding surface within the defect
reconstruction.
In addressing these specific requirements, surgeons may employ various approaches.
Since lateral ankle is a watershed area between two angiosomes, it has a relatively
poor blood supply compared with other areas of the body leading to potential poor
secondary healing.[6] Patients with diabetes mellitus or peripheral vascular disease are prone to malleolus
defect to occur and they may not be a good candidate for free tissue transfer.[7] For local flap coverage, such as reverse sural artery flap,[8] it is common for distal foot wounds to become larger due to donor site morbidity.
Adipofascial flap, composed of perforator, deep fascia, and fat layer spares subdermal
plexus and skin for donor and this makes donor site healing more effective. They were
previously employed in head and neck reconstruction[9] and lower extremity reconstruction,[4] utilizing various methods such as the adipofascial fold-down flap[10] or the venoadipofascial pedicled fasciocutaneous flap.[11] However, with deep fascia harvested together, it has possibility of muscle hernia
and injuring the nerve leading to persistent pain, altered sensation, or numbness
in the donor site. The pure fat flap, with proper dissection, can preserve deep fascia
which poses no risk for sural nerve damage.
Perforator-based propeller flaps have become a valuable tool in reconstructive surgery,[12] allowing for the transfer of tissue from a donor site to a recipient site while
preserving major blood vessels. These flaps are designed based on the concept of utilizing
specific perforating blood vessels that supply the overlying tissue. With duplex ultrasound,
a noninvasive imaging technique, we can identify the pedicle of interest and design
and elevate flap according to pedicle course looking at actual vessels. However, we
commonly encounter fat necrosis without skin necrosis after proper flap elevation
according to perforator[13]
[14] and thus circulation to subcutaneous fat (adiposal layer) could be of question.
Blood circulation in the skin is indeed facilitated by capillaries, which are tiny
blood vessels that form a dense network throughout the dermis, the middle layer of
the skin. As for fat (adipose cell), it does not have its own circulatory system like
capillaries.[15]
[16] Instead, the blood supply to adipose tissue comes from the surrounding capillaries.
In other words, adipose tissue does not have terminal branches of blood vessels like
capillaries but relies on the adjacent capillaries to maintain its metabolic functions
([Fig. 2]). The capillaries in the skin, which are part of the overall circulatory system,
serve not only the skin itself but also support the functions of underlying fat tissue.
Therefore, we suggest that adiposal layer only flap should be designed more conservatively
in smaller dimension than we would normally design a perforator-based propeller flap.
Fig. 2 Schematic illustration of fat circulation. At subcutaneous fat level, there are no
terminal capillary and cells are supplied by adjacent capillaries.
Gold standard of checking blood flow of adipose tissue is 133Xenon washout technique,[17] however it is hard to use it in clinical setting. Alternative techniques such as
Doppler ultrasound was studied, and recent study[18] comparing 133Xenon washout technique and Doppler ultrasound by Lempesis et al showed ultrasound
can be effectively used as alternative to check and quantify adipose tissue blood
flow. Thus the circulation of adiposal layer only flap was checked with color duplex
ultrasound both preoperatively and postoperatively, showing intact pedicle. Moreover,
intraoperative indocyanine fluorescent angiography helps evaluate the perfusion of
flaps,[19] and all flap perfusion was checked with indocyanine fluorescent angiography after
elevation and rotation of the flap to the lateral ankle defect. Postoperative care
is also important because stretching of flap can result in damage in pedicle such
as thrombosis or ischemia. Ankle immobilization in early postoperative period will
be important, and we used short leg cast for protection.
There have been previous reports of adiposal flap in finger reconstruction, which
used pedicled adipose tissues based on digital artery.[20] They identified digital artery and elevated preserving pedicle, but they did not
check the perfusion afterwards. With aid of indocyanine fluorescent angiography and
color duplex ultrasound, we ensured the perfusion of flap. Also, digital artery-based
adiposal flaps were much smaller compared with our flap being long as 7 to 9 cm.
Limitation of adiposal layer only flap exists. Further understanding of the vascularity
for the adiposal layer is needed. Nevertheless, this report demonstrates the possibility
and potential of using the fat only as a flap.
Conclusion
Pure fat flap or the adiposal layer only flap may be an alternative for reconstruction
in areas with large dead space, small skin defect, and joint movement. The advantages
of the pure fat flap are preserving the donor site skin, allow vascular bulk tissue
to obliterate dead space, and the fat to preserve good gliding function of the underlying
structures. By carefully addressing the specific requirements of the defect and utilizing
advanced imaging techniques, we can enhance the chances of optimal wound healing using
this approach. This technique adds to the reconstructive microsurgeon's armamentarium
for complex coverage of the ankle region.
