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Bekisz et al. Plast Aesthet Res 2022;9:61 https://dx.doi.org/10.20517/2347-9264.2022.69 Page 3 of 8

process of axonogenesis in severed nerves to a specified target, described by Cheesborough et al. as giving
[14]
“... the nerves somewhere to go and something to do” . With regard to facilitating enhanced control of the
prosthesis, harnessing the power of TMR allows redirection of neural signals intended for a missing limb
into input fed to a predefined target muscle that has been surgically stripped of all additional motor input.
This in turn reliably and predictably generates electromyographic signals that can be detected by the
prosthetic device. It is through this creation of “control sites” that electrodes from a myoelectric prosthesis
can translate neural input into meaningful movements and functions. These include transfer of a distal
branch of the radial nerve to the lateral head of triceps with the intention of facilitating hand opening and
transfer of the median nerve to the short head of biceps to drive hand closure . It is worth noting that, at
[27]
present, the limited sophistication of the lower extremity prosthetics available in comparison with those for
the upper extremity has constrained the extent to which the promise of TMR can be realized in below-knee
and above-knee amputations.

In the upper extremity, TMR is most frequently performed in patients who have sustained an injury that has
left them with no or significantly limited function proximal to the wrist . These patients can be divided
[28]
into three groups: those who have undergone an amputation in whom TMR is performed in anticipation of
eventual use of a myoelectric prosthesis; those who already use a prosthesis and desire improved control of
their artificial limb; and those opting for an elective amputation because of dissatisfaction with their current
level of upper extremity function post-injury. Amputations can be at the transradial, transhumeral, or
shoulder disarticulation level, and each TMR procedure differs with respect to the anatomy, technical
aspects, and number of control sites that can be created.

The success of TMR, and even the ability to offer it to a given patient, remains dependent on several
potentially limiting factors. Post-injury anatomy must be such that the residual nerves that will be coapted
to target muscles have not sustained damage that would preclude meaningful reinnervation, as could be
present in those with multilevel injuries or amputations involving an avulsion mechanism. Furthermore, the
patient’s residual limb must be able to tolerate a prosthetic device, which can be challenging in patients with
[27]
systemic conditions such as diabetes mellitus and peripheral vascular disease or burn injuries in whom
the soft tissue is compromised. Finally, a variety of socioeconomic factors warrant consideration before
pursuing TMR with a myoelectric prosthesis. Despite evidence that these devices can have a cost-benefit
[29]
over the lifetime , they are associated with a significant upfront cost burden, particularly for those without
adequate health insurance coverage . They also require a substantial time investment to learn how to attain
[30]
maximum functionality and are associated with high rates of abandonment [31,32] . However, regardless of an
individual’s ability to attain or operate a myoelectric prosthesis, TMR still offers the benefit of less
neuropathic pain following amputation and should be considered whenever feasible.

FREE FUNCTIONAL MUSCLE TRANSFER
FFMT entails the transposition of viable innervated tissue intended to restore some of the function that has
been lost. In upper extremity reconstruction, a typical candidate for FFMT is an individual with an avulsive
brachial plexus injury, loss or aberrant development of upper extremity musculature, or a time course of
[22]
injury and characteristics that preclude use of nerve or tendon transfers . The muscles used and the
specific techniques employed vary according to the individual’s reconstructive goals. However, common
aims include the restoration of shoulder abduction, elbow flexion/extension, and flexion/extension of the
digits.

There are several well-established workhorse flaps for each of the above aims. Shoulder abduction is often
addressed by transfer of the latissimus dorsi muscle or a combination of adductor longus and gracilis .
[33]