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 The physiology of the venous flow through flap (VFTF) places unique
restrictions on its design. The tissue farthest away from the venous plexus is
prone to congestion and necrosis. Larger flaps require a more extensive venous
plexus for complete survival. Studies have shown that VFTFs designed with a
central venous plexus with two or more efferent veins have a survival pattern
similar to that of a conventional flaps which have an inflow artery and outflow
vein. The flap on the left has a single afferent vein (left most over blue
background) and 2 efferent systems. One superficial (top right) and one
deep perforating venous system (bottom center)
A fine network of veins extending throughout the
flap is not the only factor in the VFTF's survival. Characteristics of the donor
site also play a role. There are several potential VFTF donor sites:
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Distal Volar Forearm
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Proximal Volar Forearm
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Dorsum Digit/Hand
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Dorsal Foot
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Medial Thigh/Leg
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Upper Arm
The superficial venous system located distally on
the extremity is less likely to have valves, has more extensive networking, and
is more intimately associated with and supportive of its overlying skin. This
improves the success rate making the hand, foot, and distal volar forearm
preferred donor sites for VFTFs. When a larger flap is required the proximal
forearm is the next best option. Direct visualization of the venous plexus
through the thin skin of the distal extremities allows precise design of the
VFTFs. The flap can not only be centered over the most appropriate plexus, but
creative inflow and outflow circuits can also be designed in the branching
venous system. The donor sites of small and moderate sized flaps can usually be
closed primarily.
VFTFs harvested from the leg and upper arm are
nourished by the saphenous and basilic vein respectively. These flaps are useful
when long vascular conduits or a larger soft tissue paddle is required. These
flaps are associated with increased subcutaneous tissue between the nourishing
vein and overlying skin. The smaller venous systems cannot be visualized and
their extent cannot be determined at the time of flap design. These flaps are
usually designed over the main vein. Their maximum width is restricted to insure
optimal survival.
Another limiting factor in the survival and success
of VFTFs is the recipient bed. Areas with ongoing infection can prolong healing
time and delay neovascularization of the VFTF. This can prolong the time the
flap has to rely on venous physiology and potentially decrease flap survival. In
addition, factors such as infection can result in activation of platelets and
increase thrombosis potential.
The VFTF can be harvested with additional tissues
creating a composite VFTF. This composite flap is more difficult because success
is dependent on spatial distribution of multiple components rather than just
inflow and outflow circuits. Sensory nerves such as the brachial cutaneous and
saphenous nerves have been included to create a sensate flap or to graft nerve
defects at the recipient site. Tendon has been included to reconstruct tendons,
ligaments, and joints capsules. One author has reported inclusion of tibial bone
with a saphenous venous flap for reconstruction of soft tissue and bony defects
in the hand. Theoretically, these are vascular grafts. Composite VFTFs have been
reported sporatically but no series has evaluated the efficacy of their
components as vascularized grafts.
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