Targeted muscle reinnervation (TMR)
“Targeted muscle reinnervation” has become a proven method of treatment following an amputation of the upper arm or a shoulder disarticulation. In a surgical procedure, the nerves in the residual limb that previously controlled the arm and hand are assigned a new function. They are removed from the surrounding tissue and connected precisely to muscles in intact areas of the body; for example, they can grow into the pectoral muscle. This makes it possible for the patient to control their subsequent arm prosthesis using “thought signals”.
Signals from the musculature control the hand
When the user imagines moving their phantom arm, the nerves transmit the signals to the new target musculature so that it is tensed. This results in electric signals in the millivolt range, which are measured by electrodes in the prosthetic socket. A miniature computer analyses the signals and translates them into the intended movement. If the user thinks of making a fist, for example, or closing their hand, the corresponding muscle is activated and the associated signal closes the prosthetic hand.
For the first time, TMR treatment also makes it possible to move several joints at the same time. The TMR arm prosthesis is equipped with up to six electrodes for this purpose, in contrast to conventional myoelectric prostheses, which are controlled by just two electrodes. This lets the user control up to six movements with separate muscle signals – and gives them significantly better control over the prosthesis. TMR allows the user to intuitively make faster, more precise movements with the arm prosthesis.
The TMR treatment process
Treating a patient with a TMR arm prosthesis is considerably more complex and intensive than treatment involving a conventional prosthetic device. The entire process, from the operation up to the definitive fitting, requires close cooperation between the surgeons, O&P professionals and physiotherapists. Because this process is highly tailored to the patient as an individual, it can take up to two years.
The patient is given therapy in preparation for the operation and a personal rehabilitation programme for after surgery. The most significant phase is known as “signal training”: This complex motor training ensures that the patient is able to adequately and selectively activate the newly innervated muscles. Based on this training, the O&P professional then determines the ideal position for the electrodes. Before the final prosthesis can be fitted, the user first tests a number of prosthetic sockets intended for therapy and training. The patient also gradually becomes accustomed to the weight of the prosthesis. Once the O&P professional has identified the optimal settings, he or she can fit the final socket. The physiotherapist supports the patient during the further process of learning to use the prosthesis. Regular follow-ups with the interdisciplinary team ensure the long-term success of the TMR device.
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Figure 1 – Signal training
Figure 2 – Establishing the electrode positions
Figure 3 – TMR training
Figure 4 – Targeted muscle reinnervation (TMR)