Flap design-Anatomical and physiological considerations
There is a ladder of possibilities for how a flap can be supplied by
blood. Here we try to differentiate the different flap types due to
their supply axis. Pedicled flaps can either be supplied with blood
according to a random-pattern principle or if one can define the
vascular pedicle or an anatomical axis of supply, as an axial-pattern
flap, further as an island flap (again with no definite axis). [3,
13] As was practised in the past, flaps were taken randomly and
transferred to the defect after “Autonomization”. [18]
Autonomization of random-pattern flaps is recommended when the 2:1
length-to-width ratio has to be expanded. In Autonomization, a new blood
supply by disconnecting its original blood vessels in axial or random
pattern flaps is established by elevating the flap and re-suturing it to
the graft bed. This technique not only adapts Oxygen-decrease in the
blood but curbs the arterio-venous shunts over vegetative-nervous
stimulation. Autonomization of random pattern flaps is recommended when
the 2:1 ratio from length to width is extended. [19] After the
elevated flap is sutured to his donor bed for at least three weeks, the
“Autonomized” flap is then located to the defect area for
reconstruction. Further, Autonomization can be used in axial pattern
flaps. Therefore Neo-Vascularization of the flap connects it with the
wound bed and then, after 3 to 6 weeks, the vascular pedicle can be
disconnected. [20, 21]
The use of axial pattern flaps has several advantages: Normally, no
delayed surgical procedures are
required, the skin is full-thickness and durable, and excellent cosmetic
results can be achieved. In addition, survival rates are significantly
higher for axial-pattern flaps (95%) than for flaps that do not have a
direct blood supply (53%). [22, 23]
Some examples of axial pattern flaps necessary for the Head and Neck
reconstructive surgeon are, the nasolabial flap from the angular vessels
[18], the paramedian middle-forehead flap [24] from the
supratrochlear vessels and outside the face, for example, the
supraclavicular island flap [25, 26], where
the supraclavicular artery is mostly present as an supply-axis.
Aside from axial and random pattern flaps, a third type of vascular
supply in flaps is the segmental blood supply which can be seen as a
separate flap architecture. So-called perforators, promote an
area-related blood supply from the depth to the superficial present as a
blood source. The disadvantage of these Perforator-flaps is, that they
are sensitive to traction and pressure. [18] Perforator flaps can be
pedicled or used as free flap designs with micro-anastomoses and are
usually used for the reconstruction of large tissue defects. [27]
Finally -in pedicled flaps- island flaps as a subtype of the
axial-pattern flap, are supplied with a non-defined vascular pedicle and
the skin “island” cannot be transferred without this supply. [22]
The concept of free tissue transfer through vascular anastomosis was
introduced at the turn of the last century but only saw significant
development in the 80’s. Technical innovations and an enhanced
understanding of cutaneous circulation have led to improved outcomes.
Successful anastomosis of small blood vessels was achieved in 1960 with
the use of an operating microscope. In the same decade, surgeons
explored vascular territories serviced by a single arterio-venous
system, leading to the description of axial pattern skin flaps. The
transfer of such flaps to distant sites with microvascular anastomosis
became known as ”free flaps.” [28] Compared to pedicled flaps, free
flaps exhibit distinct anatomical advantages. For one, compared to
random pattern flaps, Surgeons are no longer limited by the rule that a
flap must not be longer than it is broad (length-to-width-ratio,
normally 2:1). Vascularized tissue with a permanent blood supply can now
be introduced to devitalized areas, allowing for the repair of complex
defects in a single operation.