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Page 4 of 13 Titolo et al. Plast Aesthet Res 2023;10:21 https://dx.doi.org/10.20517/2347-9264.2022.113

In grade 3, the injury reaches the endoneurium: more scarring and disorganization in nerve regeneration
are expected, although a slow advancing Tinel sign could be recognized; under these circumstances, full
recovery is hardly achievable, and in severe cases, surgical excision and nerve reconstruction may be
required [25,26] . In grade 4, epineurium is the only structure remaining intact; Tinel sign is present at injury
level, but it does not advance due to the huge amount of fibrosis. Function restoration is such impaired that
surgical intervention is mostly required [24-27] . Neurotmesis, corresponding to a grade 5, indicates a complete
discontinuity of the nerve ends; thus, surgical intervention is mandatory to achieve functional recovery .
[24]
[28]
Lastly, Mackinnon introduced a grade 6 injury in which more traumatic mechanisms are involved; in
these “mixed injuries”, a combination of findings mentioned above can co-exist.

TREATMENTS
End-to-end neurorrhaphy
Alignment and coaptation of nerve endings with epineural microsutures are the gold standard treatment for
higher-grade axonotmesis and neurotmesis injuries [26,27] . However, it is essential to achieve tension-free
coaptation, as increased tension has been shown to negatively impact blood flow, impairing the healing
processes of the nerve; trimming the proximal and distal stumps removes nonviable tissues that might
interfere with the healing process, then nerve endings are mobilized to overcome elastic forces and achieve a
tension-free repair. As tension-free coaptation might be subjective, an idea of the proper amount of tension
can be observed by positioning only one stitch between the nerve’s ends: if the stitch can withstand the
retracting tension between the two nerve ends, it is possible to carry on the coaptation.

Finally, the nerve defect is closed with microsurgical sutures, usually 8-0 to 10-0, to minimize the formation
of foreign body scar tissue, avoiding excessive tension [24,28] [Figure 1]. In case of more proximal lesions at
wrist level, an interfascicular suture is suggested; the outer epineurium is pulled back to expose individual
fascicles which are approximated in an end-to-end fashion with a single 10-0 suture placed through the
perineurium. In order to obtain a better nerve repair, the fascicular pattern can be better identified by
observing the epineural blood vessels.

Commercial fibrin glue in nerve reconstructions is commonly used as it provides an adhesive layer
shielding the defect and, possibly, has positive effects upon inflammatory and fibrotic response; despite its
employ alone, it is still the object of dispute, the addition of fibrin glue seems to provide a useful aid to
neurorrhaphy [24,26,29] . In a study of Sallam et al., motor and sensory recovery of autologous fibrin glue
application was compared with a standard micro-suturing technique for nerve defects at the forearm and
wrist levels: the authors reported that the use of fibrin glue was as effective as microsuturing in regaining
[30]
motor and sensory functions and associated with shorter operative time .
Following surgery, a period of immobilization with plaster for three weeks is recommended to limit
movement and tension at the coaptation site in order to protect the suture, even if some authors suggest an
[31]
immobilization after isolated digital nerve reconstruction for 10 days or even shorter .
Nerve reconstruction techniques
Sometimes, the nerve’s defect could be so long to prevent suturing without excessive tension or to restrain
ends coaptation; in these cases, a nerve reconstruction is indicated. Reversed autologous nerve grafts are the
best option since they offer a reliable scaffold full of stimulating elements, such as Schwann cell basal
laminae and neurotrophic factors [26,27] . Nerve ends are prepared in the same fashion as to perform an end-to-
end neurorrhaphy; after that, the length of the defect is measured to calculate how much of the donor nerve
will be taken, estimating an extra percentage of 10% to 15% due to nerve graft’s shrinkage [24,32] . Common