Regenerative Peripheral Nerve Interface (RPNI)

Nerve injuries can occur due to a variety of reasons including trauma, surgery (including mastectomy), and amputation. Damaged nerves may form neuromas, which are a painful ball-shaped growths at the end of an injured nerve. Fortunately, a technique known as regenerative peripheral nerve interface (RPNI) can help reduce neuroma pain, post-amputation phantom limb pain, and even improve the control of advanced myoelectric prostheses.

RPNI was developed by Dr. Paul Cederna at the University of Michigan for patients with amputations. By transferring nerves that had been cut into a free muscle graft wrapped around the nerve, the grafted muscles act as signal amplifiers. These amplified signals can be detected to permit improved control of advanced myoelectric prostheses. For individuals who have access to these advanced prostheses for upper extremity amputations (shoulder disarticulation, transhumeral, or transradial), RPNI can be performed to increase the number of myosites for control of their myoelectric prostheses.

Serendipitously, Dr. Cederna recognized that patients who underwent RPNI had decreased rates of post-amputation phantom limb pain and neuroma pain. This observation has been confirmed in numerous additional studies. RPNI or a related technique known as TMR is now performed at the time of amputation at many institutions to reduce phantom limb pain and neuroma pain and to increase quality of life for amputees.

For individuals who already have undergone an amputation, RPNI remains effective for treatment of established post-amputation phantom limb pain and neuroma pain.

Any patient undergoing an amputation is a candidate for evaluation for RPNI or TMR. For patients who already have undergone an amputation and have established phantom limb pain or neuroma pain, they should be evaluated for RPNI or TMR. This often includes a physical examination to identify sites of neuromas and nerve blocks performed with an injection of local anesthetic. This involves the injection of a local anesthetic near the affected nerve or nerves. If an individual experiences significant pain relief following the nerve block, it may indicate that RPNI could be a beneficial treatment option for neuroma-related pain.

For patients interested in RPNI to enhance control of their myoelectric prostheses, they should establish a relationship with a prosthetist experienced in working with advanced prosthetic devices. The prosthetist will play a vital role in the patient's journey, ensuring proper fit and function of the prosthesis and guiding the patient through the process of learning to use their new device effectively.

RPNI surgery involves identifying the cut nerves and harvesting a small piece of muscle as a free muscle graft, either from the surgical site or from another area on the body. This muscle is then wrapped around the cut nerve, acting as a signal amplifier. This surgery typically takes less than 2 hours and is done as an outpatient procedure with same-day surgery.

Surgery typically can be done as an outpatient with same day surgery. There is usually localized post-operative pain, which quickly improves, although there may be occasional flare up of nerve pain. Prosthesis wear may resume once the wounds are fully healed, which usually is by 6 weeks post-operatively.

Be sure to see an experienced surgeon to treat this condition. Our fellowship-trained specialists at The Buncke Clinic in San Francisco treat patients using regenerative peripheral nerve interface (RPNI) from across the Bay Area and Northern California. Contact us to schedule a consultation.