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Titolo et al. Plast Aesthet Res 2023;10:21 https://dx.doi.org/10.20517/2347-9264.2022.113 Page 3 of 13

this communication can take place even in the opposite direction, in which case it is named “Marinacci
anastomosis” [12-14,17-18] . In the hand, the anastomosis between the thenar motor branch and the deep branch
of the UN is called Thenar Ansa, or Riche-Cannieu anastomosis; in this case, the involvement of motor and
sensitive fibers can lead to a hand solely supplied by the UN [17,19] .

The Berrettini anastomosis is the most frequent of the anomalies, and it is a purely sensory anatomical
alteration between the third and the fourth common digital nerve, causing alterations in the sensibility of
the middle and ring fingers [12,17] .

The third nerve innervating the wrist and the hand is the radial nerve (RN) through its superficial branch; it
is entirely sensory and, at the radial styloid, divides into several distal sensory branches which innervate the
radial region of the dorsum of the hand as well as the dorsal side of the thumb, index, middle and radial half
[20]
of ring fingers .
PHYSIOPATHOLOGICAL MECHANISMS
PNIs are traditionally classified by Seddon and Sunderland classifications.
[21]
[22]
In 1943, Seddon first proposed a division into three groups of PNIs: neurapraxia, axonotmesis, and
neurotmesis; secondly, Sunderland expanded Seddon’s classification into five grades based on the
involvement of the nerve’s structures.

Neuroapraxia, corresponding to Sunderland grade 1, means a compression or traction injury damaging
Schwann cell sheath and leading to focal demyelination but without structural nerve interruption and
degeneration; this provokes a conduction block with transient loss of function until remyelination occurs,
usually in a period ranging from hours to some weeks, with full recovery potential; at this stage, an
advancing Tinel sign is not appreciated.

When axonotmesis occurs, the damage spreads to the axon with variable involvement of the internal nerve
structures. In this scenario, a process of degeneration and regeneration, called Wallerian degeneration, takes
place within the first 48–72 hours, serving a favorable environment for axonal regrowth thanks to the
upregulation of several trophic factors served by the surrounding proliferating Schwann cells; the regrowth
can proceeds, in the right conditions, at a speed of up to 2mm/day but, since this process decreases over
time, any surgical interventions should be planned promptly [23,24] .

Progressive disruption of the internal nerve structures (endoneurium, perineurium, and epineurium)
increases the rate of scarring and intraneural fibrosis, altering perineural vascularization and disturbing
[23]
axonal regeneration and nerve recovery . Considering the prognostic relevance of this factor, Sunderland
further subdivided axonotmesis into three grades.

In grade 2, only the axon and its myelin sheath are disrupted without harm to connective structures:
denervation with loss of motor and sensory function occurs, but since the endoneurium is not involved,
poor scar tissue is produced; thus, complete nerve regeneration with optimal recovery is expected without
surgical intervention ; it is the first stage showing an advancing Tinel sign, meaning the nerve regeneration
[24]
is progressing .
[25]