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.