Selective nerve transfers, also known as TMR, can improve prosthetic function. However, to make full use of the technique, a specific rehabilitation is needed, which we present here. This protocol is well structured, making it easy to use for therapists with little experience.
Furthermore, it has been tested with over 30 patients undergoing TMR. To begin, collect the patient's medical history and ask the patient about expectations for prosthetic rehabilitation and demands for a prosthetic system in daily life. Based on this information and examination, discuss if targeted muscle reinnervation or short TMR is a good option for the patient.
Agree within the team and with the patient on performing the TMR surgery. After TMR surgery, facilitate the reinnervation process on a cortical level using mirror therapy by setting up a mirror in front of the patient. Then, ask the patient to hide the residual limb behind the mirror and instruct the patient to perform different movements with the healthy hand while watching its reflection in the mirror.
Alternatively, use the imagined movements method for the reinnervation process by asking the patient to imagine different movements of the amputated hand and arm while keeping their eyes closed. If using lateralization training, present the patient with cards that show either left or right hands and arms and ask to name the side. Then give the patient feedback on their choice.
For signal training, first, study the surgery report to understand which muscle parts are reinnervated and which nerves were transferred. Three months after the surgery, evaluate the volitional muscle activity by setting up a surface electromyographic or SEMG biofeedback system. Remove excess body hair, dead skin flakes, oil, or cream from the patient's skin to reduce impedance before explaining the goal of the assessment and the functionality of the system to the patient.
Instruct the patient to perform hand and arm movements depending on the original function of the donor's nerves and try to palpate the muscle. Place a surface EMG electrode on the skin above the muscle and if the signal amplitude during activation is two to three times higher than during relaxation, consider reinnervation to be successful. After measuring the volitional activation of all nerves, note which muscles can be activated with which motor command and ask the patient to train the motor commands at home.
Next, begin training the selective activation of the reinnervated muscles using the SEMG electrode to pick up the recipient's muscle signals and ask the patient to think of the previously evaluated movement patterns. Then display the activity of muscle using EMG biofeedback. After examining the notes from the previous evaluation, ask the patient to perform the desired movements bilaterally if it is easier.
As soon as the patient can activate the muscle, ask the patient to activate and fully relax the muscle repeatedly. Instruct the patient to perform different movements and position the electrode at different locations to find the combination leading to the highest amplitude. Once found, mark it on the skin.
If more muscles can be activated, train the activation and relaxation of each muscle individually, and when a reasonable control of the single muscle is possible, display the activity of two muscles. Start with antagonistic muscles or movements, such as hand opening and closing and instruct the patient to activate one muscle while the other one should be as relaxed as possible. Try different movement cues for both muscles if such a selective action is not possible.
Console the patient by explaining the requirement of some training for selectivity. As soon as the selective activation of two muscles is achieved, add one more muscle and repeat the procedure until the patient can selectively activate each muscle. Once the selective activation of all signals is established, introduce a tabletop prosthetic hand.
Ask the patient to control the prosthetic hand while carefully watching it, and if the prosthetic hardware allows it, explain to the patient that a low EMG amplitude corresponds to slow movement while fast movement is achieved through a high signal. Let the patient test different movement speeds. Next, activate the prosthetic elbow joint or wrist, let the patient control it, and once a good control of the signal levels is achieved, switch on all prosthetic joints and enable simultaneous control.
When the patient is fitted with a new prosthetic, explain the basic functionality of the prosthesis to the patient, such as degrees of freedom, how switching between the active joints works, the waterproof status of the prosthesis, and how it should be cleaned. Then train the patient to move prosthetic without external objects, and to do so, instruct the patient to vary the speed of movement if the prosthesis allows different movement speeds. To add more complexity, ask the patient to control the prosthesis in different positions and combine more degrees of freedom simultaneously.
For object manipulation training, provide different objects such as stress balls or wooden blocks to the patient and explain that manipulating objects adds another layer of complexity. Ask the patient to use their healthy hand to put the object into the prosthetic hand and close it. Then allow the patient to move the prosthetic elbow or wrist joint before releasing the object.
Next, place the object on the table or shelf, and ask the patient to pick it up with the prosthetic hand and place it somewhere else. Finally, train activities of daily living before the patient is dismissed from rehabilitation and uses the device at home. For the follow up assessments, invite the patient to a multidisciplinary medical consultation three months after discharge from rehabilitation.
Ask the patient about using a prosthesis at home and work or if the patient faced any issues, and assess the prosthetic function using the standardized tests. In the present study, out of 30 originally included participants, only 13 underwent prosthetic rehabilitation and 10 were available for a follow up assessment. The prosthetic function was assessed using South Hampton Hand Assessment Procedure, Action Research Arm Test, and Clothespin Relocation Tests.
In the SHAP and ARAT, higher scores mean a better function, which was also indicated by less time needed in the CPRT. We have found the use of surface EMT biofeedback extremely helpful within rehabilitation. Still, the duration of rehabilitation is relatively long due to the reinnervation of the muscle.
Our team is currently exploring how TMR changes multi-unit recruitment. We plan to use this knowledge to enhance prosthetic control in the future.
