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modifications observed in a pedicled flap such as difference in the degree of vascularization, reticulin
[18]
sympathetic stimulation that reduces blood flow to framework collapse, rate and extent of axonal
93% of normal through production of noradrenaline, regeneration and remyelination between non‑vascularized
vasoactive intestinal polypeptide, 5‑hydroxytryptamine and conventional nerve grafts.
and substance P. Most experimental models assessed
pedicled VNG affected by these factors, rather than In contrast, using a large sciatic nerve gap in the rabbit,
[24]
free ones. [19,20] Settergren and Wood. showed in their Restepo et al. found that VNGs in all time periods
[17]
canine model a better blood flow after 4‑6 days for studied (from 5 weeks to 15 weeks) did better in terms
NVNG compared to a VNG. A free VNG, not affected of remyelination and number of axonal fibers than did
[25]
by sympathetic stimulation, would likely eliminate this conventional nerve grafts. Shibata et al. reported results
difference. on 40 rabbits median nerve grafts (20 vascularized and
20 nonvascularized). Although there were no significant
While NVNGs, when placed in a well‑vascularized differences in nerve conduction, action potential, and axon
bed, undergo a 72 h period of warm ischemia prior to diameters, there were statistically significant differences
neovascularization, VNGs do not. [16,17] When placed in in muscle contraction force (20% greater in VNGs than
a nonvascularized bed, the ischemic period last up to NVNGs and comparable to the healthy control side) and
14 days for a short NVNG (30 mm nerve graft in rats), axon counts. Kanaya et al. reported that the vascularized
[16]
[26]
while VNGs have no ischemia time. Despite remaining sciatic nerve graft group showed a better mean sciatic
avascular for 14 days, NVNGs eventually regained their function index (SFI) (n = 30, SFI = ‑64 ± 11) than
[27]
vascularity and performed better than VNGs on nerve the nonvascularized sciatic nerve graft group (n = 27,
conduction velocity studies. [16,17] Still it is unclear if this SF = 99 ± 7) (P < 0.01). A SFI of ‑100 represents a
has any clinical relevance. complete loss of function of the nerve. There was also a
The above findings were observed in thin small animal significantly higher nerve conduction velocity in the VNG
nerves. It is likely that a larger nerve, such as a human group. This was the only study to evaluate the resulting
mixed nerve of a limb, is not as efficiently revascularized function instead of morphologic parameters. In a normally
from the surrounding bed as the small nerves investigated vascularized bed, VNGs appear to perform better. Kärcher
in animal models. Clinical experience has shown that small and Kleinert evaluated recovery following a 1.5 cm
[28]
cable grafts are required to make a large caliber nerve that sciatic nerve defect in rats repaired with a pedicled
will be efficiently revascularized. [10‑12] Revascularization femoral nerve graft with the creation of an AV fistula
might not reach the core in a NVNG while a VNG stays of the femoral vessels. He reported better and faster
well‑perfused. regeneration of a VNG that was complete at 5 months, but
which was incomplete in the NVNG.
REGENERATION IN VASCULARIZED Scarred (nonvascularized) wound bed
NERVE GRAFTS VERSUS Koshima and Harii tried to replicate a scarred
[29]
NONVASCU‑LARIZED NERVE GRAFT wound bed using a rat burn wound model with nerves
transplanted into silicone tubes. They demonstrated an
Although the mechanism is not clear, VNGs appear to increased size and density of myelinated axons and earlier
provide more effective regeneration than NVNGs. This regeneration of nerve fibers in VNGs as compared to
difference becomes more evident and functionally relevant conventional nerve grafting.
as length and caliber of the graft increase and as wound
[16]
vascularization decreases. No comparison has been made Mani et al. did not find any significant difference in
in the clinical setting, but clinical reports generally agree nerve conduction velocity studies between vascularized
that VNGs provide faster regeneration. and non‑VNGs in avascular graft beds, even following
a prolonged initial period of revascularization for
Studies of VNGs in animal models have reported non‑VNGs.
conflicting results. For the purpose of clarity, we have
divided the following discussion into studies performed Functional results
on a vascularized bed and studies performed on a Prior studies have produced conflicting results secondary
nonvascularized bed. to a lack of homogeneity in evaluation methods. As
[26]
previously noted, Kanaya et al. reported in their work
Normal (vascularized) bed that the vascularized sciatic nerve graft group showed a
McCullough et al. found no difference between significantly better mean SFI than the nonvascularized
[21]
[27]
vascularized and nonvascularized grafts when studied sciatic nerve graft group.
by electrophysiological examination and the degree
of axonal regeneration. In a similar rat sciatic nerve Several authors had reported superior results when placing
model, Seckel et al. found no differences in number VNGs where previous conventional nerve grafts had
[22]
[30]
of regenerated axonal fibers, amount of intraneural already failed. Rose and Kowalski reported good results
scarring, or thickness of regenerated myelin sheaths. with the dorsalis pedis artery‑peroneal nerve complex in
Pho et al. performed histological studies in eighteen five cases with a digital sensory nerve reconstruction in
[23]
rat femoral nerves. Their experiment showed no the setting of prior failed non‑VNGs.
Plast Aesthet Res || Vol 2 || Issue 4 || Jul 15, 2015 185