Northwestern Medicine researchers evaluate unique surgical method to treat chronic amputee pain

Northwestern Medicine® researchers are leading a new multi-center clinical trial to evaluate a unique surgical method, known as targeted muscle reinnervation (TMR), to treat chronic pain that can result from limb amputation. Around a quarter of all amputees develop chronic pain in the remaining portion of their amputated limb, which can include phantom limb syndrome (pain that is perceived in the portion of the limb that is gone), and prevents many patients from using prostheses. While there are many causes for amputation, more than 1,000 active military personnel have had a major limb amputation due to combat-related injuries in recent conflicts.

Northwestern Memorial Hospital is the lead site for the four-year study, "Targeted Reinnervation as a Means to Treat Neuromas in Major Limb Amputation," which is funded by the Department of Defense's (DoD) Office of Congressionally Directed Medical Research. Other participating sites include Walter Reed National Military Medical Center, The University of Washington Medical Center and Harborview Medical Center, and San Antonio Military Medical Center as participating sites.

"The problem for amputees that experience chronic pain isn't that the limb itself was removed," said Northwestern Medicine's chief of plastic surgery and principal investigator for the study, Gregory A. Dumanian, MD. "The problem is that the nerves that used to control the amputated limb are incomplete, but also remain active, constantly sending signals to the brain. These separated nerves cannot heal properly without the chance to connect to other nerve tissue, and end up creating painful growths called neuromas."

The current standard of care for a painful amputee neuroma is to remove the nerve growth and then place the nerve ending into a nearby muscle for extra cushioning. While this treatment can reduce neuroma pain, it is not always successful and still leaves the nerve active and disconnected to inevitably create a new neuroma.

The TMR therapy's goal is to transfer a nerve that has been cut-off from the muscles it used to control and essentially plug it into a functioning muscle nearby. This is accomplished by removing the neuroma from the damaged nerve, and then surgically joining it with a healthy nerve that controls the existing target muscle. Joining these nerves together allows them to then grow into, or reinnervate, the target muscle and prevent the neuroma from reforming.

"TMR is a completely new approach to treating neuroma induced pain for amputees," said co-investigator Todd Kuiken, MD, PhD, a Northwestern Medicine physiatrist who is director of the Center for Bionic Medicine at the Rehabilitation Institute of Chicago (RIC) and professor of surgery at the Northwestern University Feinberg School of Medicine. "Instead of trying to treat a painful neuroma by burying it, this procedure provides damaged nerves with a new purpose. After TMR, patients can use these previously unable nerves to contract their target muscle and their repurposed signals can even be detected and used to control prostheses."

TMR was pioneered in 2002 by Dumanian at Northwestern Memorial in conjunction with Kuiken in order to address the rehabilitation needs of amputees. Since 2002, TMR has now been performed successfully more than 100 times worldwide and nearly all of the patients who had painful neuromas before the procedure reported no neuroma pain afterward.

"By giving an amputee's damaged nerves a new purpose, we have seen TMR improve many lives," added Dumanian, who is also a professor at the Feinberg School of Medicine. "Now we have the chance to test TMR in a large clinical trial which will allow us to take the next steps toward the possibility of making it a new standard of care."

The clinical trial will use an online pain questionnaire and MRI imaging of the nerves treated before and after surgery to compare the outcomes of TMR and the current standard surgical treatment for painful neuromas. The research is supported by the DoD's Office of Congressionally Directed Medical Research grant OR120021 and will seek to enroll a total of 200 individuals across all four centers, making it the largest neuroma study ever performed.