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Page 2 of 13 Titolo et al. Plast Aesthet Res 2023;10:21 https://dx.doi.org/10.20517/2347-9264.2022.113

treatments and outcomes makes hand PNI a potential challenge for hand surgeons; to achieve satisfactory
results, it is important to have a clear knowledge of peripheral nerves anatomy at the wrist and hand level, of
the physiopathological mechanisms occurring after trauma, of the strategies that have been developed to
treat them and the proper timing of management.

ANATOMY
Sensory and motor innervation of the wrist and hand is guaranteed by three nerves: median, ulnar, and
radial nerves.

The Median Nerve (MN), just before entering the carpal tunnel, releases the palmar cutaneous branch of
the median nerve , which supplies afferent fibers to the palmar surface of the hand as a constant structure,
[6]
[7]
occasionally mentioned as absent in literature ; this sensory branch common spring from the radial side of
the MN at an average distance of 4.1cm to 8.4 cm proximal to the volar wrist crease, with a mean length of
the nerve spanning from 2cm to 15cm [8-10] ; the palmar cutaneous branch of the median nerve has been
shown to possess in several studies a high anatomical variability of both pathway and branching which are
[11]
complicating factors in predicting its location during surgical procedures .
Exiting the carpal tunnel, MN splits into a medial ad a lateral branch. The first and the second palmar
common digital nerves originate from the medial branch; they provide motor fibers for the second
lumbrical muscle and sensory fibers for the distal palm, the third finger, half of the index finger and, usually,
half of the ring finger; from the lateral branch, instead, arise the thenar motor branch and the first three
palmar proper digital nerves innervating the first lumbrical muscle and supplying sensory innervation to the
radial half of the index finger and the thumb; possible variants of the anatomical pathway of thenar motor
branch have been studied, but in the most frequent cases it arises from the radial side of MN, distal to the
[12]
transverse carpal ligament .

In the ulnar-palmar wrist region, the Ulnar Nerve (UN), emerging from underneath the flexor carpi ulnaris
tendon, releases the dorsal branch of the UN nerve. This branch directs dorsally and carries sensitive fibers
to the dorsal-ulnar region of the hand and supplies sensitive innervation of the hypothenar eminence
[13]
thanks to small branches ; subsequently the UN enters Guyon’s canal, where, approximately at the level of
[12]
the distal edge of the pisiform, splits into a superficial and a deep branches: the superficial branch divides
further into the proper digital nerve of the little finger, the common digital nerve of the fourth web space, a
cutaneous branch for the palmar surface and a motor branch for the palmaris brevis muscle; the deep
branch is purely motor and travels deep and ulnar in relationship to the superficial branch, commonly
giving off firstly, inside or outside the canal, fiber for the abductor digiti minimi muscle, it then curves
radially around the hook of the hamate, along with the deep branch of the ulnar artery, providing motor
innervation for the hypothenar muscles, adductor pollicis and flexor pollicis brevis [14,15] . Lumbrical and
interosseous muscles also possess variable innervation: the first and second lumbrical usually receive motor
innervation from MN branches; instead, the third lumbrical gets both UN and MN innervation up to 64%
of the cases ; interosseous muscles innervation is often provided by the deep branch of the UN, but it has
[16]
been demonstrated, during autopsy studies, that in up to 3% of cases, the first dorsal interosseus is
[12]
innervated by MN .

To complicate the scenario, many anastomoses between the UN and MN can occur, altering pathways of
innervation. The Martin-Gruber anastomosis occurs in the forearm between the anterior interosseous nerve
(or the MN itself) and the UN; it carries motor fibers from the proximal MN to the distal UN, serving
principally the first dorsal interosseous muscle and, possibly, the hypothenar muscles too [12,17] . In rare cases,