Keywords keystone flap - local flaps - perforators
Introduction
The keystone design perforator flap was first described by Behan[1 ] in 2003 as a trapezoid island flap based on a random vasculature consisting of perforators
running along the major axis of the flap. The major advantages presented in Behan's
first presentation regarded its adjustability and easy dissection and the fact that
it allows closing cutaneous defects with reduced tension. These features made the
keystone flap a workhorse in limb and trunk reconstruction from the very beginning.
Since then, it has been widely modified to make it suitable for different reconstructive
demands.[2 ]
[3 ]
[4 ]
[5 ]
[6 ]
[7 ]
The design of the keystone flap requires the defect to be elliptical-shaped, with
the long axis parallel to the cutaneous nerves, veins, and arteries from which the
cutaneous perforators detach. The skin adjacent to the defect is bluntly dissected
respecting the 1:1 (width of the defect:width of the flap) ratio and advanced until
wound approximation is reached. When required, a deep fascial incision along the outer
border of the flap provides further advancement.
In the last few years, this easy-to-harvest island flap has gained increasing popularity
in the fields of both posttraumatic and postoncologic resection reconstruction. The
keystone design perforator island flap (KDPIF) is indeed suitable for covering wide
full-thickness soft-tissue defects that would otherwise require more time-consuming
free or myocutaneous flaps, still providing functional and aesthetically pleasant
results.
This article aims to present a single-center experience with this type of flap, highlighting
its great pliability and versatility. Here are described some modifications we have
adopted to make the KDPIF safer and a valid competitor to more challenging flaps.
In particular, the major objective of this retrospective study was to underline how
a flap (which has always been considered based on random vasculature) could easily
become a perforator flap to meet peculiar reconstructive demands. Knowing the exact
location of perforators allows the surgeon to undermine a larger portion of the flap
without the fear of injuring the vascular supply, providing a better resurfacing of
a cutaneous defect.
Materials and Methods
Patients with skin defects who underwent reconstructive surgery using a KDPIF from
January 2020 to May 2023 at our department were retrospectively reviewed. Given the
retrospective nature of the study, approval of the ethical committee was not necessary.
All patients enrolled in the study had signed an informed consent prior to surgery.
Demographic data (age, sex, characteristics of skin defects, comorbidities, smoking
habits), type of KDPIF, postoperative complications, wound dressing, and follow-up
were revised. All the patients underwent accurate surgical debridement of the wound
before preparing the flap. Four KDPIFs were used to reconstruct the lower leg area,
2 for the neck region, 1 for the shoulder, 1 for the fourth finger of the hand, 1
for the ischiatic area, 4 for the skin overlying the Achilles tendon, and 1 for the
skin overlying the knee. The average defect size was 15.9 cm2 (range: 2–48 cm2 ). All classical KDPIF variants were utilized: type IIA was the most frequent (6 patients,
46.2%), followed by type IV (3 patients, 23.1%; [Fig. 1 ]), then type IIb (1 patient, 7.7%), type III (1 patient, 7.7%; [Fig. 2 ]), and type I (1 patient, 7.7%). Patients' demographics are listed in [Table 1 ].
Fig. 1 (A ) Ulcerated lesion (which later was diagnosed as a squamous cell carcinoma) of the
lateral subpatellar region in an 87-year-old man. (B ) Flap marking; type IV keystone design perforator island flap (KDPIF). (C ) Picture of the fully healed lesion at the 1-month follow-up.
Fig. 2 (A ) Postradicalization tissue defect. Detail of the underlying Achilles tendon. (B ) Preoperative marking of the type III keystone design perforator island flap (KDPIF)
before radicalization of a Merkel cell carcinoma of the Achilles tendon region in
a 62 year old man. The perforators were marked as red dots. (C ) Immediate postoperative. Two suction drainages in place.
Table 1
Patients' characteristics and demographics
Age (y)
Sex
Indication
Body area
Comorbidities
Complications
Keystone type
Tissue loss dimension (cm2 )
34
M
Caustic burn
Shoulder
None
Partial posterior dehiscence
IIA
48
14
M
Retractive scar
4th finger—hand
None
None
IV (no skin graft)
2
79
M
Basal cell carcinoma
Neck
IHD
Partial posterior dehiscence
IIA
25
48
M
Pressure ulcer
Ischiatic
None
None
IIA
12
87
M
Squamous cell carcinoma
Lateral leg (proximal one-third)
None
None
IV (with skin graft)
20
48
M
Chronic osteomyelitis
Anterior leg (lower one-third)
None
None
IIA
18
80
M
Basal cell carcinoma
Lateral-anterior leg
DM, hypertension
Minimal dehiscence
IIA
6
74
M
Basal cell carcinoma
Neck
None
None
IIA
22
75
F
pT1 sarcoma
Achilles' tendon region
DM, hypertension
Partial flap loss
IV (with skin graft)
21
73
M
Hardware exposure
Knee
hypertension
None
IV (with skin graft)
10
62
M
Tendon exposure
Achilles' tendon region
None
None
IV (with skin graft)
4
83
F
Basal cell carcinoma
Lateral leg
None
None
IA
6
62
M
Merkel's cell carcinoma
Achilles' tendon region
None
None
III
16
Complications were divided into major (complete or partial flap loss) and minor (wound
dehiscence and wound infection). All the patients were dismissed from the hospital
within 10 days with bland analgesics (nonsteroidal anti-inflammatory drugs [NSAIDs],
acetaminophen). The minimum follow-up period was 30 days.
Each patient underwent preoperative evaluation and selection of suitable perforators
near the defect to treat and the flap marked upon, using a handheld ultrasound (US)
color Doppler probe (Clarius L20 20 MHz).
This preoperative study of the perforators allowed us to model better the flap preserving
its original shape, while also giving us the confidence to undermine the flap as needed
or to even skeletonize the perforators when deemed necessary.
The surgery was performed under local anesthesia plus sedation or general anesthesia.
Even when the tumors or cutaneous defects were located on the limbs, we did not use
a tourniquet. The excisions were designed elliptical and the markings were done taking
into account the size and location of the evaluated perforators. Possibly, dissection
of the deep fascia was avoided and the perforator area was preserved with no need
to fully skeletonize the perforators. Resorbable sutures (Monocryl 2–0 and 3–0) were
used for skin closure of the double lateral V-Y advancements and for closing the outer
curvilinear line. The “front” of the flap was closed using a monofilament, nonresorbable
suture (Prolene). Three patients were treated with Negative Pressure Therapy (NPT)
applied above surgical incisions and skin grafted areas (where present) for 7 days
postoperatively at a pressure of –90 mm Hg, whereas the majority of patients were
treated with classical wound dressing. Antibiotic ointment (fusidic acid) was used
daily for 15 days on sutures only. No antibiotic therapy was administered a priori.
Results
The analysis of our medical records reported a total of 13 patients treated with a
KDPIF from January 2020 to May 2023. The average age was 63 years (range: 14–87 years),
and all the patients were nonsmokers. Six patients (46.2%) suffered from hypertension,
ischemic heart disease, or diabetes. Basal cell carcinoma (Basal Cell Carcinoma [BCC])
excision was the most frequent cause (30.8%), followed by previous trauma (23.8%),
decubitus ulcer (7,7%), retractive scar correction (7,7%), squamous cell carcinoma
(Squamous Cell Carcinoma [SCC]) excision (7,7%), sarcoma resection (7.7%), Merkel's
cell carcinoma radicalization (7.7%), and knee hardware exposure (7.7%). As regards
posttraumatic reconstructions, one patient was treated for a third-degree caustic
burn of the shoulder, one patient experienced wound dehiscence and Achilles' tendon
exposure after surgical tendon repair ([Fig. 3 ]), and another patient had a chronic ulcer of the lower leg ([Fig. 4 ]). The follow-up ranged from 7 to 36 months, with a mean follow-up period of 13 months.
Minor complications occurred in three cases (23.1%) and did not compromise the overall
outcome. They were treated with local wound care and no patient required hospitalization
or surgical revision. We experienced one major complication (7.7%) in a patient in
which the KDPIF was used to resurface the Achilles tendon area. The flap suffered
from partial superficial necrosis and required surgical revision and coverage with
a split-thickness skin graft. Notably, the patient suffered from diabetes and did
not strictly stick to the given directions. Details regarding complication rates and
management are specified in [Table 2 ].
Table 2
Complication rates and details
Postoperative complication
N (%)
Body region
Management
Major complication
1 (7.7%)
Complete flap loss
–
–
Partial flap loss
1 (7.7%)
Achilles' tendon region
NPT, toilette + skin graft
Minor complication
3 (23.1%)
Wound dehiscence
2 (15.4%)
Shoulder, lower leg
Local wound care
Wound infection
1 (7.7%)
Neck
Local wound care, oral antibiotics
Fig. 3 (A ) Preoperative picture of wound dehiscence after surgical tendon repair in a 62-year-old
man. (B ) Marking of the type IV keystone design perforator island flap (KDPIF) with evidence
of the main perforator (red cross ). The dotted line separates the part of the flap that will be raised underneath the fascia (right side)
from the one that will remain mostly untouched (to preserve the perforator). (C ) Immediate postoperative picture shows the details of the grafted donor site. The
split-thickness skin graft was meshed 1:1.5.
Fig. 4 (A ) Preoperative picture of a chronic wound with underlying chronic osteomyelitis of
the anterior region of the leg in a 48-year-old man. (B ) Marking of the type IV keystone design perforator island flap (KDPIF) with evidenced
of the main perforator (green cross ). (C ) Immediate postoperative. One suction drainage in place.
Discussion
Unlike free flaps or perforator flaps, the KDPIF is simple in its dissection and does
not require any preoperative imaging. Behan first described four variations of the
flap, each one suited for specific reconstructive issues. Type I does not allow fascia
dissection and is suitable for defects up to 2 cm in width; type IIA is ideal for
greater cutaneous defects located over muscular compartments since the deep fascia
has to be dissected along the outer curvature of the flap; type IIB differs from type
IIA for the grafting of the donor area in body regions where excess tension cannot
be mitigated; type III is chosen when resurfacing larger cutaneous defects (up to
10 cm) since it consists of two juxtaposed keystone design flaps. Type IV facilitates
resurfacing of joints since it may be raised with subfascial undermining up to 50%
of its size.
Several other modifications, as the omega variant and the Sydney Melanoma Unit variation,
have been described during the last decade.[8 ]
In this article, we have illustrated how it is possible to adapt the KDPIF to everyday
surgical practice. The additional Doppler study of the nearby perforators prior to
surgery allows surgeons to perfectly tailor the flap and makes it safer by identifying
and thus preserving vascular supply, nevertheless avoiding pedicle dissection. This
procedure is not vital for a positive outcome when using this flap, but we still prefer
to perform it since it is easy and not time-consuming, and it allows surgeons to perform
a more reliable procedure in body regions where the paucity of blood supply represents
a major problem. We deem the keystone flap particularly adequate when there is the
need to resurface wide cutaneous defects quickly and easily, especially in patients
in which microvascular flaps are not an option.[9 ]
[10 ]
Even if we usually think about the KDPIF as the first reconstructive option when feasible,
we also recommend it as a great backup flap for secondary reconstruction or in combination
with other regional flaps to overcome reconstructive challenges.[11 ]
Key points about skin reconstruction with a KDPIF are listed:
It is “easy to design” and can adapt to different reconstructive demands. It is therefore
a very approachable flap, especially for young surgeons and institutions for which
a more complex flap might become challenging. Unlike perforator flaps, the KDPIF does
not have a steep learning curve and can be easily tailored on the patient.[12 ]
Microscope and microsurgical instruments are not needed, which means that there is
no need for a microsurgery-experienced surgeon, either. Nevertheless, the lack of
magnification does not make the KDPIF a “hazardous” flap: the reliability of blood
supply lies on its design and orientation, which allow random perforators to be included
in the skin island. This theory was first formulated and confirmed by Milton in 1971,[13 ] when he published the experiments that gave him the idea that a cutaneous pedicle
was not only unnecessary but also possibly detrimental to flap survival. From these
first studies, Behan could conceive of an island flap that was sufficiently wide to
contain enough perforators and with a design that evenly distributes tension forces.
There is no need to skeletonize perforators. This can be a tedious procedure that
sometimes engages surgeons for a great amount of time. The KDPIF does not rely on
a single perforator, so its design is easy and this translates into a reduction of
operating and surgical planning time.
It can be adapted to almost every region of the body. Several authors have described
its use not only for limb and trunk reconstruction but also for resurfacing soft-tissue
defects located on the face, hands, and feet,[14 ] slightly modifying the original markings.[15 ]
[16 ]
[17 ] Although the KDPIF is a naturally “thin” flap (its harvesting does not include muscle
masses), it can be in part de-epithelialized, buried, and grafted to fill deeper defects.
The KDPIF is perfectly suitable for lower limb reconstruction.[4 ]
[6 ] The paucity of alternatives makes it a workhorse flap when it comes to resurfacing
soft-tissue defects in these body areas, in particular above the joints. The amount
of subcutaneous tissue included in the KDPIF is usually sufficient to protect noble
structures, without providing the annoying bulky effect that is typical of myocutaneous
flaps. This also means that refining “touch-up” surgeries are usually not necessary,
leading to easier and quicker recovery and, consequently, swifter access to rehabilitation
and normal mobilization.
The lymphatic drainage is somehow preserved despite the island nature of this flap.
Probably, blunt dissection preserves a part of the deep lymphatic drainage and this,
combined with the incision of the superficial cutaneous lymphatics, might lead to
a lymphangiogenetic stimulus that may guide a quicker-than-usual restoration of the
lymphatic flow. This leads to an extremely rare incidence of pincushioning and trap-door
deformity, and the postoperative flap swelling is greatly minimized.
The KDPIF is a flap with both a low rate of major and minor complications that are
easily treated most of the times. Furthermore, for this type of reconstruction, flap
loss can be considered a rare event.
We were able to achieve excellent results with various types of KDPIF applied to different
reconstructive demands across the entire body surface. The main limitations of this
study are represented by the small sample size and the different applications of this
typology of flap. Results may vary according to the location and the size of the defect
to be reconstructed; specifically, we would not recommend the use of the KDPIF when
reconstructing defects located on the face because of the major risk of distortion
of aesthetically relevant structures. As described earlier, we routinely use this
flap in case of upper and lower limb reconstruction as well as for covering defects
located on the thorax or above mobile joints.
Conclusion
The KDPIF is suitable for all body areas “from the scalp to the feet” thanks to its
curvilinear shape, which made it apt to resurface mostly all cutaneous defects consequent
to tumor resection or trauma. Together with preoperative US-assisted planning, we
deem this flap very versatile and safe, a real workhorse flap if not the first choice
in selected cases.
