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Figure 1. Expanded reconstructive ladder with targeted muscle reinnervation, osseointegration, and vascularized composite
allotransplantation. TMR: targeted muscle reinnervation

necessitates creating a proximal motor nerve that is now disconnected and left with no target. However,
unlike pure sensory or mixed motor-sensory nerves, these cut pure motor nerves do not form symptomatic
neuromas. In fact, contrary to initial reservations, TMR was found to substantially reduce post-amputation
[18]
pain in upper extremity amputees .
The discovery that TMR had the potential to reduce post-amputation pain drastically expanded its
indications. The majority of amputees suffer from chronic pain after amputation that can prevent fitting
of a prosthesis. While a state-of-the-art myoelectric prosthesis may not be practical for every amputee,
a procedure with the potential to reduce chronic pain ballooned in popularity amongst amputees. With
this in mind, surgeons have now turned to employing TMR at the time of amputation to prevent post-
[19]
amputation pain .
Below, we provide an overview of the indications, techniques, and future directions of TMR in upper and
lower extremity amputees, both at the time of amputation and as a secondary procedure. With additional
experience using TMR and advancements in prostheses, we will continue to see a shift in functional
expectations after amputation from both surgeons and amputees alike.

Upper extremity TMR
The development of upper extremity TMR was primarily driven by the desire for more natural, intuitive
prostheses. Loss of a hand or upper extremity is profoundly limiting. While body powered prostheses help
fill this functional void, they cannot recapitulate all of the degrees of freedom of a human upper extremity,
particularly with higher-level amputations. They also do not allow for simultaneous movements across
multiple joints. As such, there was a push to overcome the shortcomings of traditional prosthesis, chiefly
[20]
funded by the Defense Advanced Research Projects Agency Revolutionizing Prosthetics Program .
TMR was an answer to the call for more intuitive, higher capability prosthetic control. By providing a
neural interface with the prosthetic using multiple discrete high-amplitude EMG signals, it has exhibited
excellent results for real time control of upper extremity myoelectric prostheses for the last decade [17,21,22] .
The upper extremity amputee now has several commercially available myoelectric prosthetic options to
choose from [21,23] . Moreover, as signal processing and pattern recognition algorithms continue to improve
the neural interface between patient and prosthetic, amputees benefit from more natural prosthetic
movement [24,25] .