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Page 4 of 17 Qiu et al. Plast Aesthet Res 2022;9:19 https://dx.doi.org/10.20517/2347-9264.2021.126

Neurolysis of common compression sites may augment functional recovery. Decompression relieves any
existing insult to the nerve and prevents the development of new compression neuropathies as a result of
PNI induced neural edema - perhaps limiting axonal injury and clinical symptoms under the double crush
[19]
hypothesis .

One of the most challenging clinical scenarios is a nerve injury in continuity. We currently lack
intraoperative tools to ascertain the presence of viable axons regenerating beyond the injury site that have
yet to synapse with end organs. We therefore must rely on clinical assessment of the nerve appearance and
its consistency on palpation. A bulbous segment of nerve tissue that is firm and pale is suggestive of a
neuroma in continuity. This is classified as an axonotmetic injury with partial or complete damage to the
internal architecture of the nerve (Sunderland grade II-IV) that can impede spontaneous regeneration
beyond the injury. If a large neuroma-in-continuity affecting the entire diameter of the nerve is
encountered, complete excision to healthy appearing fascicles followed by interposition nerve grafting is
typically indicated. If a partial neuroma-in-continuity is encountered, perhaps with some muscle
contractions elicited by direct electrical stimulation proximal to the injury site, an internal neurolysis can be
considered to free intact fascicles and reconstruct only the injured portions of the nerve. However, the
surgeon should proceed with caution so as not to downgrade any baseline function or remove the potential
for spontaneous recovery. In the scenario of a partial neuroma-in-continuity, it is often wise to avoid
surgical interventions at the injury site and consider distal end-to-side nerve transfers when these options
are available.

When one encounters a complete neuroma-in-continuity or nerve transection, resection and nerve
reconstruction are indicated if the lesion is thought to be causing neuropathic pain. If the patient is not
experiencing pain originating from that lesion, the surgeon must consider whether nerve reconstruction has
the potential to restore motor or sensory function and whether the benefit and likelihood of success
outweighs the ensuing deficits created from harvesting nerve graft or nerve transfers. Intraoperative neural
monitoring and electrodiagnostics are particularly useful in this setting, as the absence of nerve action
potentials across the neuroma in continuity would motivate resection and reconstruction over neurolysis
alone [20-22] . However, the potential for successful reconstruction depends on the likelihood of innervation
prior to advanced denervation-induced atrophy. With time, denervated muscle undergoes progressive,
irreversible atrophy with fibrosis and degradation of myofibers and motor endplates [23,24] . As such, surgeons
must consider the time elapsed since injury, the regenerative distance, and the innate regenerative capacity
of the patient based on age and comorbidities. Assuming that nerves regenerate at a rate of roughly 1 mm
per day or 1 inch per month and that reinnervation must occur within 18 months of denervation, the
regenerative distance for a proposed surgical plan can be used to determine the favorability for meaningful
motor recovery [Figure 1] . If the regeneration distance is favorable, then primary repair or secondary
[25]
grafting should generally be attempted.

The advent of distal nerve transfers expanded the window of opportunity in which surgical intervention can
be considered by decreasing the regenerative distances required to reinnervate target muscle groups. This
requires the availability of a healthy donor nerve with redundant or expendable function in close enough
proximity to allow for an end-to-end or end-to-side coaptation sufficiently distal to the site of injury. When
performing nerve transfers, the donor nerve should be transected as distally as possible to facilitate a
tension-free distal coaptation to the recipient nerve and the recipient nerve should be transected as
proximally as needed to provide additional redundancy if needed. If the redundancy is not needed, the
recipient nerve stump is typically trimmed to prioritize a distal repair, minimizing the regenerative distance.
Donor nerve selection should also be mindful of any agonism/antagonism vis-a-vis the function to be