Page 39 - Read Online

Azoury et al. Plast Aesthet Res 2020;7:4 I http://dx.doi.org/10.20517/2347-9264.2019.44 Page 5 of 20

fascicular transfer may allow even greater prosthetic control through the creation of an array of individual
[30]
EMG signals . Finally, while all currently available prostheses rely on visual feedback, future prostheses
[21]
will integrate a sensory feedback loop to allow more effective patient interaction with their environment .
Finally, as new surgical techniques develop, so will indications for TMR versus transfers of existing
musculature for prosthetic and pain control. Already, it is possible for metacarpal level amputees to obtain
excellent finger function with the starfish procedure, in which existing interosseous muscles are dorsally
transposed to create a reliable myoelectric signal . In this same patient, a sensory neuroma may be
[31]
resected and the nerve coapted to a motor nerve to the volar interosseous for pain control. Future success
will depend on balancing pain control and function with the most effective surgical technique available.

Lower extremity TMR
While the use of myoelectric prostheses in the upper extremity is somewhat common, it has been modest in
the lower extremity . This is likely partially related to the relatively recent introduction of lower extremity
[32]
TMR when compared to the upper extremity. However, it also appears that sensory and proprioceptive
feedback of both the amputated limb/prosthesis and the contralateral unaffected limb play a much more
important role in developing an intuitive and natural lower extremity prosthesis. Moreover, in the absence
of widespread TMR in the lower extremity, there has been some success in developing myoelectric
prostheses that rely on EMG signals from the existing innervated musculature in the amputated limb [33,34] .
Although TMR in the lower extremity may allow more nuanced control of a myoelectric prosthesis, it is
possible to control movement as distal as the ankle even with a transfemoral amputation using pattern
[35]
recognition from the remaining thigh musculature .
In the absence of widely available lower extremity prostheses that rely on TMR, much of the conversation
surrounding lower extremity TMR has focused on treating and preventing nerve-related pain. For decades,
traction neurectomy was the standard of care during amputation, which has proven ineffective in both
[36]
preventing and relieving post-amputation pain . For many patients, the decision to amputate is driven by
chronic pain, and they are frustrated to find that they trade the pain prior to amputation for new forms of
chronic pain after amputation.

This new pain includes pain at their residual limb site, known as residual limb pain (RLP), and painful
sensations in their absent extremity, known as phantom limb pain (PLP). RLP is usually due to neuroma
formation. These neuromas stem from the terminal sprouts that form at a transected nerve end after injury
primarily and are comprised of disorganized, sensory nerve fibers. PLP is thought to be due to sensory-
cortical remapping over time and an altered perception of pain. With standard amputation methods, the
rates of post-amputation pain were astounding, with over 55% of longstanding amputees suffering from
RLP, and the prevalence of PLP after lower extremity amputation ranging as high as 85% [37-40] .

Lower extremity TMR was first employed to treat the pain many of these existing amputees had suffered
from for years. While several prior methods had achieved moderate success in treating post-amputation
nerve pain, such as implanting nerves into bone, veins, or muscle [41-43] , these methods do not treat the
underlying pathophysiology - they simply provide some mechanical masking of neuromas so they are less
likely to result in pain. Conversely, TMR prevents the formation of disorganized nerve growth that results
neuromas by providing a pathway for nerves to grow down and a denervated target to reinnervate.

After its established success as a secondary intervention for post-amputation neuromas, attention shifted
[44]
to the use of TMR at the time of amputation as a means to prevent pain . Several case series have
demonstrated excellent results, although efforts at conducting a randomized control trial comparing TMR
to standard methods (i.e., implantation into muscle) were thwarted by patient refusal of randomization due