TECHNOLOGY IN MEDICINE
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Figure 4 - TMR transfer to Pectoralis Major segments for EMG-monitored
and microprocessor-controlled myoelectric prostheses designed
for high-humeral amputations. C is the musculocutaneous nerve (n.)
TMR to the pectoralis clavicular segment. SC is the median n. TMR
to the pectoralis upper sternal-costal segment. E is the radial n. TMR
to the external (lower) segment. S are EMG sensors connected to the
microprocessor (MP). A are Latissimus Dorsi and Serratus Anterior
alternative recipient muscles.
transfer of the median nerve and anastomosis to the nerve of the
biceps muscle short head for “hand closing” signals. The musculocutaneous
innervation of the biceps long head is left for “elbow
flexion” signals, and the proximal radial nerve to the triceps long
head is left for “elbow extension” signals. If the brachialis is present,
the ulnar nerve is transferred and anastomosed to its nerve for wrist
function. EMG sensors in a cuff around the skin over these upper
arm muscles signal the microprocessor to produce the desired
prosthetic actions.
These TMR patterns are chosen to follow normal synergistic
use, when possible, which provides prosthetic control that is intuitive,
or near-intuitive. This gives great advantage over previous
prosthetic technology.
PAINFUL NEUROMA MANAGEMENT
An unexpected benefit from TMR has been a decrease in painful
neuromas, which often follow amputations. 7 Transected sensory
nerves given neural sheath conduits for regeneration beyond the
amputation site are less prone to painful neuroma formation than
those with “nowhere to go.” Thus, TMR is being used for established
neuroma pain, and for prevention in nerve transections at high risk
for such pain. Although not always successful, the benefits address
a troublesome problem that has been most resistant to solutions.
SENSORY RESTORATION: THE LIMITATIONS TO TMR-CON-
TROLLED PROSTHETICS
Sensation and sensory feedback for fine motor control are necessary
to provide the most functionally effective upper limb use. To date,
this remains an unsolved problem in TMR-controlled prosthetic
technology. Some localized finger and hand sensations from skin
closely overlying the re-innervated muscle segments are detectable
after TMR. Potentially, these could be better defined and linked to
touch and pressure sensors placed in the prosthetic hand. Investigators
are currently exploring these phenomena for potential use. 8
Studies include placing surface network grids of multiple EMG
sensors, which detect multiple signals and their complex patterns
for analysis by the microprocessor (“pattern recognition analysis.”)
Direct sensory nerve stimulation is also being studied. Sensory feedback
and more refined prosthesis control are goals of these efforts.
CURRENT STATUS OF UPPER LIMB REPLACEMENT
As hand transplantation enters its third decade of clinical application,
it remains the best treatment for functional and cosmetic upper limb
restoration, but careful candidate screening, diligent compliance and
lifelong immunosuppression are required. 3,4 The useful sensation and
sensory feedback restored by hand transplantation is not currently
matched by TMR-controlled prostheses, and the TMR-controlled
prosthetic abandonment rate remains high. 9 Thus, widespread use
would require substantial technologic advances.
Investigators pursuing progress in VCA and TMR-controlled
prosthetic technology have great opportunities and challenges.
Surgeons and investigators at UofL are field leaders who continue
to make significant contributions. We strive to bring more perfect
limb restorations to today’s amputees and to the Luke Skywalkers
of the future.
References
1. Tobin GR, Kaufman C, Jones C. The world’s first successful hand transplant
at 20 years: background, consequences, and future. Louisville Med. 2019
Jan;66(8):21-23.
2. Kuiken TA, Barlow AK, Hargrove L, Dumanian GA. Targeted muscle reinnervation
for the upper and lower extremity. Tech Orthop. 2017Jun;32(2):109-116.
3. Tobin GR, Breidenbach WC, Klapheke MM, Bentley FR, Pidwell DJ, Simmons
PD. Ethical considerations in the early composite tissue allograft experience: a
review of the Louisville ethics program. Transplant Proc. 2005;37:1392-1395.
4. Kaufman CL, Bhutiani N, Ramirez A et al. Current status of vascularized
composite allotransplantation. Am Surg. 2019;85:631-637.
5. Tobin GR. Pectoralis major segmental anatomy and segmentally split pectoralis
major flaps. Plast Reconstr Surg. 1985;75:814-824.
6. Tobin GR. Segmentally split pectoral girdle muscle flaps for chest wall and
intrathoracic reconstruction. Clin Plast Surg. 1990;17:683-696.
7. Dumanian GA, Potter BK, Mioton LM, et al. Targeted muscle reinnervation
treats neuroma and phantom pain in major limb amputees: a randomized
clinical trial. Ann Surg. 2019;270:238-246.
8. Wolf EJ, Cruz TH, Emondi AA, et al. Advanced technologies for intuitive control
and sensation of prosthetics. Biomed Eng Lett. 2019 Aug 8;10(1):119-128.
9. Salminger S, Sturma A, Roche AD, et al. Outcomes, challenges and pitfalls ater
targeted muscle reinnervation in high-level amputees: is it worth the effort?
Plast Reconstr Surg. 2019;144:1037e-1043e.
Dr. Tobin is a professor at the University of Louisville School of Medicine, Department
of Surgery, Division of Plastic and Reconstructive Surgery. He practices with UofL
Physicians – Plastic and Reconstructive Surgery.
Dr. Jones is an associate professor at the University of Louisville School of Medicine,
Department of Surgery, Division of Hepatobiliary and Transplant Surgery. He serves
as Director of the Trager Transplant Center and is Director of the UofL Health/
University of Louisville VCA Program.
Dr. Kaufman is the Scientific Director of the UofL Health/University of Louisville VCA
Program and a faculty member of the Department of Cardiovascular and Thoracic
Surgery in the School of Medicine. (non-member)
18 LOUISVILLE MEDICINE