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Page 6 of 17 Toyoda et al. Plast Aesthet Res 2022;9:17 https://dx.doi.org/10.20517/2347-9264.2021.118

With traction neurectomy, the problematic nerve is held in traction and the terminal end excised so that
once relaxed, it is cut in a much more proximal position, thereby relocating the sensitive end to a position
that is more likely to be protected by soft tissues. These passive/ablative procedures have so far had mixed
[37]
results. In a study by Sehirlioglu et al. of 75 lower extremity amputees with neuroma pain who were
treated with traction neurectomy relatively early in their symptom development, no neuroma recurrence
[38]
was noted at a mean follow-up of 2.8 years. On the other hand, a retrospective cohort study by Pet et al. of
38 patients who were older than the Sehirlioglu study and presented multiple years after symptom
development, which had a 42% recurrence rate and 21% required subsequent surgical treatment. Given
these mixed results for passive neuroma management, advances in TMR and RPNI for symptomatic
neuroma treatment hold hope for these patients.

TARGETED MUSCLE REINNERVATION
History of TMR
TMR is a technique in which the cut ends of the problematic sensory nerves are coapted to nearby motor
nerves of redundant muscles. The sensory nerve fascicles are thereby provided with terminal receptors,
which are thought to prune axonal sprouting . TMR was originally developed to make use of redundant
[39]
muscle and nerves in amputees for improved use of upper extremity myoelectric bioprosthetics [39-45] .
Myoelectric prostheses use electromyography (EMG) signals from the residual limb to control the motors of
the device. TMR, RPNI, and agonist-antagonist myoneural interfaces are the three main means of deriving
stable, high signal-to-noise ratio signals from muscles . Ideally, the controls are in independently
[46]
controlled muscle groups with minimal extraneous EMG noise from nearby musculature, termed muscle
[42]
cross-talk . Without TMR, there is typically only one pair of independent control sides in the residual limb
for prosthesis control (i.e., the extensors and flexors at a joint). However, with TMR, new myoelectric
control sites are available, allowing for multiple joint movements while simultaneously bioamplifying the
signals to increase signal capture by surface electrodes and reduce relative muscle cross talk, which is
especially beneficial for those with very proximal amputations [42,47] .

One of the first patients who received TMR had bilateral humeral disarticulations in which the median,
radial, ulnar, and musculocutaneous nerves were transferred to the pectoralis major and minor muscles.
[40]
According to Hijjawi et al. , this patient demonstrated significant improvement in myoelectric device use.
In another patient with an amputation at the humeral neck, TMR was performed to motor nerves of the
pectoral and serratus muscles . The patient reported intuitive control as well as the sensation that the
[43]
appropriate phantom limb sensations were transferred to her chest upon light touch . Early studies in
[43]
transhumeral amputees demonstrated signs of reinnervation in 8-12 weeks and sufficient EMG signals for
prosthesis operation in 5-7 months . In a study by Miller et al. with six transhumeral or shoulder
[44]
[48]
disarticulation patients, all patients found prosthesis use to be easier with TMR control compared to
conventional control, and this was corroborated with improvement in the performance of clothespin and
box-and-blocks tests. For upper extremity prostheses, TMR has been described in combination with free
muscle transfers such as a free myocutaneous gracilis flap in those lacking adequate soft tissue coverage for
prosthesis use . In this patient without biceps muscles, who therefore had a limited number of target
[42]
[42]
muscles, the free gracilis also served as additional nerve targets .
TMR has also been studied in conjunction with machine learning algorithms to optimize prosthesis use.
Pattern classification techniques could be applied to surface EMG signals of upper extremity amputees so
[50]
[49]
that pattern recognition could be used . A randomized crossover study by Hargrove et al. evaluated
direct control compared to pattern recognition myoelectric prosthesis control in nine transhumeral
amputees. After 6-8 weeks of at-home trial, most patients preferred pattern recognition control, opening a