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Page 6 of 13 Titolo et al. Plast Aesthet Res 2023;10:21 https://dx.doi.org/10.20517/2347-9264.2022.113

barrier against scar formation, and their non-immunogenic structure causes a less inflammatory response
[40]
and possesses enough permeability to allow diffusion of neurotrophic elements . Skeletal muscle tissue
possesses longitudinally oriented basal lamina and extracellular matrix elements that orient and stimulate
regrowing nerve fibers and, furthermore, limits the risk of vein collapse [40,41] . The surgical technique is quite
easy: the vein graft ends are sutured in a similar manner as previously explained with other types of
[42]
conduits . Advantages of this method are many: easy availability of graft materials, no comorbidity to the
donor site, immunological compatibility of the grafts, and low costs; unfortunately, the technique’s major
downside is its current limitation to short nerve defects treatment (< 3 cm) [41,42] .

Nerve transfers
Other options have been developed to bypass nerve gaps; nerve transfers have been traditionally employed
in brachial plexus lesions and in proximal nerve injuries, but subsequently, they also gained popularity for
[43]
the restoration of hand function in distal nerve injuries . They are defined as the surgical coaptation of a
healthy donor nerve to a recipient nerve proximal to its target, sharing a similar principle to tendon
transfers in which a more useful distal function is restored by sacrificing another function that is less
[44]
important to the patient .

This procedure has many advantages: bringing the donor nerve closer to the target reduces nerve
regeneration time and accelerates functional recovery, and a motor-to-motor or a sensory-to-sensory nerve
transfer can optimize regeneration potential; unlike tendon transfers, the sacrifice of a donor nerve branch
with a singular function can compensate the loss of a nerve which possesses many. In addition to that, nerve
transfers do not need to modify the muscle’s insertion and vector and the recovered function is closer to the
original muscle function, thereby achieving synchronous physiologic motion [44-46] . Nerve transfers are
indicated when nerve reconstruction would require an excessively long nerve graft, or in case of low-quality
of the proximal stump, or when delayed surgery is performed; contraindications include situations in which
better options are available (such as a simple end-to-end neurorrhaphy), when the excessive time between
injury and reinnervation occurs, or when donor nerve motor function is below Medical Research Council
grade 4 [24,44,45] .

It is mandatory, prior to performing the transfer, to test donor nerve function with a nerve stimulator and,
at the same time, to confirm the lack of function in the recipient nerve; following the law of “donor-distal,
recipient proximal”, the donor nerve is transected as distally as possible while the recipient nerve as
proximally as possible in order to maximize the length of each nerve branch and to perform a tension-free
repair [24,45] .

In case of MN defects, restoration of the motor branch to thenar muscles is essential to the thumb’s
opposition movements, and this problem can be solved by transferring the anterior interosseous nerve
branch to the pronator quadratus to motor branch, usually using an interposition nerve graft; although a
good match in size between the donor and recipient is achieved and effective results have been reported by
different authors, the employ of nerve graft causes the loss of some regenerating axons, thus, reducing the
potential of reinnervation [45,47,48] .

Possible alternatives reported in the literature involve the transfer of the third lumbrical motor branch (UN)
or the motor branch to the extensor digiti minimi and extensor carpi ulnaris (RN) with mixed results [43,49] ; in
recent years, transfer of the motor branch of the abductor digiti minimi muscle (UN) proposed by Bertelli et
al. has shown encouraging results , while in a novel cadaveric study, Abou-Al-Shaar et al. described an
[50]
interesting technique involving the motor branch to flexor digiti minimi brevi (UN), favoring this nerve due