Plastic surgeons want to use nerve regeneration to make prosthetic limbs move

Plastic surgeon Paul Cederna, MD, has always been interested in solving some of the most challenging issues in reconstructive surgery. He co-leads the Neuromuscular Lab at the University of Michigan, which focuses on developing futuristic technology that uses an amputee's nerves to control a prosthetic limb.

This next-generation technology may sound like the stuff of science fiction movies; still, Cederna and his lab colleagues have combined the regenerative power of peripheral nerve cells with biotechnologies to bring this technology closer to becoming a reality.

"When I was a kid, one of my favorite shows was the 'Six Million Dollar Man,' and astronaut Steve Austin crashed his test plane into the ground – lost an arm, an eye and both his legs, and they rebuilt him better than he was before," said Cederna. "Stronger. Faster. We're working on it every single day to achieve those goals."

Still a long way to go

He said the technology is not there yet, but he works every day to achieve his goal – to give amputees back the hand or leg they had before their accident and make sure that their prosthetic limb moves as it should.

A critical problem for those who have lost an extremity is the lack of control and sensory feedback in arm and hand prosthetics. Many patients find everyday tasks such as carrying something, shaking hands or using a smartphone difficult or impossible.

In the United States, over 185,000 individuals undergo amputation annually. That's nearly 500 per day. Approximately two million people overall have lost an extremity. While upper extremity prosthetics have advanced over the years, much work still needs to be done to improve their functionality.

The biotechnology Cederna is developing is grounded in the knowledge that peripheral nerves can regenerate, unlike central nervous system cells.

"When you have an amputation, the nerve is just trying to grow back to where it was before," said Cederna. "When it has no target to grow to, you develop a neuroma on the end of the nerve."

A neuroma is an extensive collection of nerve fibers that is incredibly painful to an amputee. It can prevent them from wearing a traditional prosthetic and even keep them awake at night.

Making a connection

"So, we thought to connect with the peripheral nerve," said Cederna. "And at the same time, address the issues the patients are having with the neuroma, and this is where the concept of the regenerative peripheral nerve interface came from."

Cederna's plastic surgery background helped him attach a muscle to the end of the nerve to give it a target or something it wants to do. The nerve regenerates into the muscle just like it did before the amputation happened.

"Not only can we control the neural pain and the phantom pain, but we also get huge amplification or nerve signals which allows us to get that high fidelity, fine digital dexterity that we're going to want out of any prosthetic device," said Cederna.

Collaboration at its best

The Neuromuscular Lab brings together a collaborative team with extensive expertise in multiple areas to solve the complex problem of combining limb loss with a biotechnologically-advanced prosthetic. Stephen Kemp, PhD, is an assistant research professor and plastic surgery co-director at the lab.

"The primary goal of the neuromuscular lab is to get an amputee to play the piano with their prosthetic hand," said Kemp. "The way that we do that is by creating a nerve machine interface. What I mean by that is that the patient's own nerves will control a prosthetic hand, so they'll be able to move the prosthetic hand naturally like a human hand."

In addition, Kemp said the amputee will also be able to feel the prosthetic hand like a normal hand, sensing touch, temperature and pain, which isn't possible right now in any prosthetic limb.

"We're the engineering team. So, it's our job to take these beautiful signals that Dr. Cederna is creating by attaching muscle to the ends of nerves," said Cindy Chestek, PhD, an associate professor of biomedical engineering. "Then we apply machine learning algorithms to those nice, pretty, big signals and use that to control prosthetic hands."

This project aims to take people who have lost a hand and enable them to control a prosthetic hand at the level of individual fingers just by thinking about it.

"There are amazing opportunities for us, and I'm so excited every single day to be able to have this job," said Cederna. "It is an honor and a privilege to be able to serve our communities in this way, to serve our patients in this way and actually to help our specialty move forward."

To find a qualified plastic surgeon for any cosmetic or reconstructive procedure, consult a member of the American Society of Plastic Surgeons. All ASPS members are board certified by the American Board of Plastic Surgery, have completed an accredited plastic surgery training program, practice in accredited facilities and follow strict standards of safety and ethics. Find an ASPS member in your area.