Rehabilitation Biomechanics Laboratory - RPNI and Electrode FAQs

Frequently Asked Questions About RPNI Research Studies

Researchers at the University of Michigan are developing new ways to improve how people control advanced prosthetic limbs. This research uses regenerative peripheral nerve interfaces (RPNIs) and implanted recording electrodes to study the signals that remain in nerves after amputation. By understanding these signals, we hope to develop prosthetic control systems that are more intuitive, reliable, and responsive. Below we address frequently asked questions about RPNIs and our on-going research studies. Questions are divided into those about the surgery, living with implanted electrodes, and those about the study procedures.

Questions About the Surgery

Are there any risks to having RPNIs?

Risks are primarily associated with the surgery required to create an RPNI rather than the RPNI itself. These risks include:

Infection
Side effects from anesthesia
Post-operative pain and discomfort

There are certain conditions and factors that could interfere with an RPNI developing properly and connecting to new blood vessels. These may include:

Vascular Disease
Nutrition Deficiency
Corticosteroid Use
Immunosuppression
Nicotine Usage

Are there any risks to implanting electrodes?

There may be risks associated with the electrodes used in research studies. These risks can be separated into those specific to the surgery and those associated with the wires exiting the skin.

Risks of surgery include:

Infection
Side effects from anesthesia
Post-operative pain and discomfort

Risks of the wires include:

Infections and/or skin irritation at the exit sites

How long does the electrode implantation surgery and recovery take?

As part of research, electrodes may be placed into existing RPNIs or inserted at the same time the RPNIs are created. Either surgery can take approximately 2-4 hours. The specific duration will depend on the location of amputation and number of RPNIs created.

After the surgery, study participants stay in the hospital until their pain is well managed. This depends on prior history and whether additional surgeries, such as limb revision, are done as part of the same surgical procedure. For prior participants, this time period has ranged from 1-7 days.

What is an exit site?

An exit site is the specific spot on your body where small wires from your implanted electrodes exit the skin so they can connect to external recording equipment.

When not in use, the wires are secured in an external holder placed on your body and covered with a waterproof dressing. Before surgery, you will meet with a surgeon and/or prosthetist to choose the best location for your exit site based on your current prosthesis, anatomy, and daily routine.

When can I start wearing my prosthesis again?

It is important to wait until the wound on the residual limb fully heals before wearing a prosthesis. On average, this takes about six weeks.

Are there any reasons a patient should not get this surgery?

Since the tiny muscle graft relies on the surrounding tissue to stay alive, the area must have excellent blood flow. Certain medical conditions can affect healing or blood flow and may make RPNI surgery less appropriate. The study surgeon will review each potential participant’s history to ensure they are a good candidate.

Questions About Living With Implanted Electrodes

Is there anything to be aware of or precautions to take when getting my surgical site(s) wet during a shower or bath? Are there any restrictions on products I use in the shower/bath?

The one area that needs special care is where the wires exit your skin. This spot needs to stay clean and dry, without soap or water getting on it directly. During your dressing changes, you'll clean around the wire exit site with an alcohol pad instead.

You can shower and wash your hair and body with whatever soap or shampoo you normally use — there are no product restrictions for most of your skin.

Can I go swimming?

Swimming in a clean, chlorinated pool is generally permitted after the surgical incision has healed. The wire exit sites must remain clean and dry and should be covered with a waterproof dressing before entering the water.

Can I still exercise?

During the first several weeks after surgery, participants should avoid strenuous exercise and activities that could place excessive stress on the surgical sites. Light daily activities, such as walking and climbing stairs, are generally encouraged as tolerated. Recommendations for returning to more vigorous exercise will depend on healing and should be discussed with the clinical care team.

Can I have MRI scans after this surgery?

Participants with implanted research electrodes cannot undergo MRI while the electrodes remain implanted because the electrodes contain metal components that are not MRI compatible.

If you need medical imaging, please let your care providers know about your implant so they can discuss safe alternative imaging options with you.

Will my electrodes set off metal detectors or impact flying?

The implanted electrodes are not expected to set off airport metal detectors or interfere with commercial air travel.

Can I sleep in my usual position after surgery?

Most participants are able to return to their usual sleeping position after the surgical sites have healed. Recommendations during the initial recovery period may vary depending on the location of the wire exit sites.

Questions About Study Procedures

When do experiments begin and how long do they last?

Once the RPNIs have healed and the nerve has grown into the muscle graft, participants may begin study visits, depending on their recovery and the study schedule (typically around 3 months after surgery). The number and length of experiments depends on the specific study and can be found on clinicaltrials.gov:

Transhumeral RPNIs for prosthetic control and sensation
Transradial RPNIs for prosthetic control and sensation
Transfemoral RPNIs for prosthetic control and sensation

What happens to the electrodes when someone is finished with their part in the study?

Once your participation is complete, you will have the choice to undergo either a partial or total removal (explantation) of the electrodes. Your surgeon will walk you through the pros and cons of each option to help you decide what is best for you.

Both explantation options are outpatient procedures.

Can I still participate if I live far from the University of Michigan campus?

Yes! We can offer mileage reimbursement and hotel accommodations for those who travel 120 miles or more to reach the University of Michigan campus.

Can I still use nicotine while in one of the studies?

No. Nicotine use—including cigarettes, vapes, or chewing tobacco—is not permitted for at least one month prior to enrollment or at any point during the study. Nicotine can restrict blood flow to surrounding tissues, which hinders the RPNI's ability to establish a healthy blood supply.

Will I have to pay for parking while I am participating in a lab session?

No. You will not have to pay for parking while participating in the study. We provide free on-site parking at the School of Kinesiology, as well as access to nearby parking structures.

What if I’m not eligible for any current studies?

If you aren't eligible for our active studies, we recommend joining the University of Michigan O&P Registry. By signing up, you can be notified if a new study matches your profile in the future.

Click on the link above to sign up!

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