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WHAT IS THE THEORETICAL divides into two branches which course along the nerve;
ADVANTAGE OF A VASCULARIZED (4) multiple dominant arterial pedicles; and (5) multiple
NERVE GRAFT? dominant arterial pedicles which form a continuous artery
accompanying the nerve.
A VNG should be theoretically result in a more According to the authors, the best nerves for use as VNGs
functional nerve for several reasons: (1) vascularization are the superficial radial nerve and the deep peroneal
is maintained: revascularization of the nerve graft nerve (type 2 grafts), the saphenous nerve (type 4 graft)
restores the extrinsic neural blood vessels; (2) reduction and the ulnar nerve (type 5 graft). [14]
of intraneural fibrosis secondary to ischemia facilitates Taylor and Ham also classified peripheral nerves according
[7]
axonal regeneration; (3) faster reinnervation reduces to their blood supply with special reference to their
denervation muscle atrophy; and (4) maintenance of suitability for microvascular free transfer:
vascularization promotes faster Wallerian degeneration (1) Type A: considered to be the ideal nerve for free
and clearance of myelin debris, reducing obstruction to transfer, as the neurovascular bundle contains a long
axonal growth into the graft with faster remyelination of unbranched nerve that receives a segmental blood
regenerated axons.
supply from a single parallel arteriovenous (AV) system.
Nerves have both an extrinsic and intrinsic blood supply. The superficial radial and ulnar neurovascular bundles,
The extrinsic system consists of arteries and veins that the posterior and anterior tibial neurovascular bundles
accompany a nerve outside of its epineurium for a and the median nerve with the brachial artery belong
variable distance along its length. The intrinsic system to this type; (2) Type B: similar to Type A, but the nerve
consists of epineural, perineural and endoneural vessels branches early and must be reversed to avoid axonal
running longitudinally within the nerve. The two systems loss, provided that the unidirectional flow of the veins
freely interface through the vasa nervorum, which pass is taken into account. The intercostal neurovascular
through the mesoneurium. bundle or the radial nerve with the profunda brachii
artery belong to this type; (3) Type C: long unbranched
Conventionally, interpositional nerve grafting interrupts nerve supplied by a single large nutrient vessel; the
both the extrinsic and intrinsic systems, which can be median nerve when supplied by a large median artery
restored only by peripheral neovascularization. Lind and or the sciatic nerve when its arteria comitans is the
[8]
Wood suggested that early ischemia of conventional dominant supply belong to this type; (4) Type D: long
nerve grafts may be associated with sufficient graft unbranched nerve which receives nutrient branches
necrosis to hinder the stromal function of the graft as a from different “parent” vessels of various diameters.
conduit for advancing axons.
The sciatic nerve in the thigh belongs to this type.
Revascularization of a nerve graft is carried out in two Conversely, the sural nerve and the meodial cutaneous
ways: vessels from the surrounding tissue bed grow nerve of the forearm are usually unsuitable, as the
into the graft tissue (centripetal revascularization) and “parent” vessels which give rise to the nutrient branches
vessels from the end of the graft sprout into the existing are small and diverse; and (5) Type E: branching nerve
vascular tree (inosculation). Vascular ingrowth from the with a fragmented blood supply; a most unsatisfactory
surrounding tissues is the most important. [8,9] As donor situation for free transfer. The posterior cutaneous
nerve caliber increases, the ability for neovascularization nerve of the forearm, the cutaneous nerves of the
to reach the center of the nerve decreases. [2,5] thigh, and the saphenous nerve in the calf belong to
Experimental and clinical evidence have confirmed that a this type.
critical diameter is reached beyond which central necrosis
will result. [10‑12] IS VASCULARIZATION OF A VNG
SUPERIOR TO THAT OF A NVNG?
DO VNGs HAVE AN EFFICIENT
VASCULARIZATION? Yes, vascularization of a VNG is considered to be superior
as it possesses an independent blood supply that avoids
Several clinical and experimental studies have demonstrated ischemia eliminating the need for revascularization from
that free and pedicled VNGs do have an efficient the surrounding wound bed. It is speculated that this
vascularization, that their extremities bleed well after avoids core necrosis and eventual scarring within the
isolation and transfer, that they are well‑perfused and that graft and maintains Schwann cells viability. [7]
their anastomoses stay patent. [13]
Although it has been shown that VNGs are efficiently
It has been postulated that VNGs can be performed vascularized, it can be postulated that revascularization
without the need for venous anastomosis because they of a NVNG can, under certain conditions, be as efficient
drain through their cut ends. El‑Barrany et al. have as a well‑vascularized bed. NVNG remain nonvascularized
[14]
described five types of nerve vascularization patterns for 3 days in a well‑vascularized bed and for up to
[15]
in relation to their feasibility for harvest as VNGs: 14 days in a nonvascularized bed. The flow across
[16]
(1) no dominant arterial pedicle; (2) one dominant NVNG then catches up and is even superior to that of
arterial pedicle; (3) one dominant arterial pedicle that VNG. This difference can be explained by the flow
[17]
184 Plast Aesthet Res || Vol 2 || Issue 4 || Jul 15, 2015