Figure 2 - Matt Scott showed Dr.
Breidenbach and Dr. Tobin early
function of his ground-breaking
transplanted hand in 1999. It would
become the World’s first long-term
success.
Rickelman, who received his transplant at Jewish Hospital in 2011,
reported that function of his hand is so fully restored that he often
forgets it is a transplant. This is an ideal outcome.
The success of the Louisville effort stimulated a new transplantation
field, “vascularized composite allotransplantation (VCA),”
with more than 30 active clinical programs in the US, Europe and
Asia. The UofL VCA program has now been active for nearly 25
years, and it continues national and international leadership in VCA
clinical trials and translational research.
RECENT TECHNOLOGY ADVANCEMENTS IN PROSTHETICS
Experience with hand transplantation demonstrated that it is appropriate
for only a very select patient population, not all amputees. 4
This presents opportunities for alternative technologies. One has
recently emerged that promises substantially improved prosthetic
function by pairing a microprocessor-controlled myoelectric
prosthesis with a new surgical procedure called Targeted Muscle
Reinnervation (TMR). In TMR, key nerves previously divided by
the amputation are surgically re-routed and anastomosed to nerves
of selected nearby muscles. Each recipient nerve is transected to
receive the transferred nerve, and neurons of the transferred nerve
regenerate through the recipient nerve sheath to its motor endplates.
This converts the muscle to control by the transferred nerve, which
can be detected by electromyographic (EMG) signals. EMG signals
are much more easily detected than nerve conduction signals, so
the muscle becomes a biologic amplifier of the transferred nerve’s
signals. EMG sensors placed on the overlying skin detect these amplified
signals, and direct them to a microprocessor in the prosthesis,
which is programmed to control specific actions of the prosthesis. 2
TRANS-HUMERAL AMPUTATIONS AND TMR
The most promising application of TMR-controlled prosthetic
technology has been in trans-humeral (above-elbow) amputations.
Improvised explosive devices in the Iraq and Afghanistan wars
created large numbers of such injuries. Trans-humeral amputations
have been exceptionally challenging to both prosthetic solutions
and to full-arm transplantation, as functional results of both are
substantially inferior to hand/forearm transplants. In shoulder
TECHNOLOGY IN MEDICINE
disarticulations and very high-humeral amputations, no
limb muscles remain to receive TMR transfers. Instead,
adjacent chest-wall muscles, especially pectoralis major
muscle segments, are used. These applications are based
on segmental muscle anatomy and innervation, which
were first described by our research in the UofL Plastic
Surgery laboratories 5,6 (figure 3). A common TMR protocol
that uses this segmental anatomy is shown in figure 4. The
musculocutaneous nerve remaining above the amputation
site is transferred and anastomosed to the nerve of the
pectoralis muscle clavicular segment, which will then
respond to the transferred nerve. This response is detected
by an overlying EMG sensor connected to the microprocessor,
which is programed to cause “elbow flexion” of the
prosthesis. Similarly, the median nerve remaining above
the amputation site is transferred and anastomosed to the
nerve of the pectoralis upper sternal-costal segment, which
will generate EMG signals to the microprocessor for “hand-closing”
of the prosthesis. The radial nerve remaining above the amputation
site is transferred and anastomosed to the nerve of a third muscle
segment to generate signals to the microprocessor for “hand-opening”
of the prosthesis. This TMR anastomosis is either to the nerve
of the pectoralis external segment (figure 4) or to the nerve of the
latissimus dorsi muscle. Alternatively, a serratus anterior muscle
segment, or a transposed pectoralis minor muscle may be used. The
ulnar nerve remaining above the amputation site is transferred and
anastomosed to a muscle segment nerve left unused after the TMRs
described above are done. There is no fixed hierarchy of options,
and both recipient nerve availability and size guide the choices.
In low trans-humeral amputations that preserve motor endplates
to the triceps and biceps muscles, anatomically distinct components
of these muscles are split and selectively used for TMR transfers
and prosthesis control via the microprocessor. A pattern commonly
used is transfer of the distal radial nerve and anastomosis to the
nerve of the triceps lateral head for “hand opening” signals, and
Figure 3 - Segmental neurovascular anatomy of the pectoralis major
muscle, as first identified in studies at the University of Louisville
Plastic Surgery laboratory. Muscle segments are shown at left, and
their independent neurovascular supplies are at right.
(continued on page 18)
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