A new technique known as targeted muscle reinnervation (TMR), where severed nerves in the amputated limb are rerouted to other muscle targets, is showing impressive reductions in debilitating phantom limb and stump pain in patients with below-knee amputations.

Pioneers of the technique, Ian Valerio, MD, and Byers Bowen, MD, Ohio State University Wexner Medical Center, Columbus, describe how to perform the procedure in below-the-knee amputation and report their outcomes in an initial group of patients in an article published in the January 2019 issue of Plastic and Reconstructive Surgery.

They explain that losing a limb because of trauma, cancer, or poor circulation can result in phantom limb and stump pain in upwards of 75% of amputees.

Over the course of 3 years, the surgeons performed 22 TMR surgeries on below-the-knee amputees. Results show that none of the patients developed symptomatic neuromas and only 13% of patients who had the procedure at the time of amputation reported having pain 6 months later.

“We are seeing phenomenal results with this technique, with much better pain control, a large reduction in the use of painkillers, and easier use of prosthetics,” Valerio told Medscape Medical News.

At the time of amputation, the researchers identified and rerouted the peripheral nerves.

“We connect the cut nerves to other nerves around them so they reinnervate other muscles,” he explained. “This allows the body to reestablish its neural circuitry. It gives the cut nerve somewhere to go and something to do.”

They have found a large reduction in pain, including symptomatic neuroma — where the prosthetic presses on nerves causing pain — residual limb pain, and phantom limb pain.

Valerio prefers to perform the rerouting procedure at the time of amputation (primary TMR) rather than conducting a second operation months or years later after the patient reports severe pain (secondary TMR).

“With primary TMR patients only have to have one surgery. The operation takes a bit longer, as we have to dissect out the nerves and transfer them, but we are seeing a fourfold reduction in pain and less narcotic use, which is a tremendous advantage in the current environment of the opioid crisis,” he said.

He estimates the average number of nerves that need to be rerouted is about three to six.

The surgery is now being performed at several centers, including Ohio State University, Walter Reed National Military Medical Center, Northwestern Memorial Hospital, and Massachusetts General Hospital. An additional 15 to 20 centers plan to offer the procedure soon, Valerio reported.

He and his team now offer training to surgeons who want to learn the technique at Ohio State, partially funded by the US Department of Defense.

In a press release by Ohio State, the dean of the institution states the current article “provides a blueprint for improving patient outcomes and quality of life following amputation.”

Valerio and Bowen note that TMR was first developed to allow amputees better control of upper limb prosthetics. Traditionally, the surgery was performed months or years after the initial amputation. It was later discovered the procedure also improves certain causes of pain, and it started to be used to treat symptomatic neuromas and/or phantom limb pain.

In the article, they give a detailed description of the surgical technique for TMR used for below-knee amputation and introduce primary TMR, when the procedure is performed concurrently with amputation.

Valerio and Bowen report that they have performed TMR on 22 below-knee amputees — 18 primary and four secondary procedures — since 2015.

Whereas multiple studies have reported a prevalence of symptomatic neuroma of 2% to 25%, “none of our below-the-knee TMR patients have developed symptomatic neuromas postoperatively with mean time since operation of 18 months,” they say.

In addition, although 72% of the primary TMR cohort experienced phantom limb pain in the first month, this “abruptly declined” to 19% at 3 months and 13% at 6 months.

“This corresponds with the timeline of reinnervation with return of voluntary muscle twitches noted at 3 months,” they comment.

“We hypothesize that primary TMR has the advantage of preservation of longer peripheral nerve length than traditional traction neurectomy, permits rapid nerve in-growth and reinnervation of target muscle, and potentially greater neuroplasticity to possibly alter the pain circuits and central pain up-regulation,” they conclude.