Rerouting Nerves Reduces Post-Amputation Pain

Rerouting severed nerves in below-knee amputations into surrounding muscle prevented symptomatic neuromas and reduced phantom limb pain, researchers reported.

None of 22 amputation patients who underwent the nerve reassignment procedure — known as targeted muscle reinnervation (TMR) — developed symptomatic neuromas over an average of 18 months, according to Ian Valerio, MD, of the Ohio State University Wexner Medical Center in Columbus, and co-authors.

And of 18 patients who had TMR performed concurrently with their amputation surgery, only 13% reported phantom limb pain at 6 months, they wrote in Plastic and Reconstructive Surgery.

While previous studies have shown TMR can reduce phantom limb pain and peripheral neuropathy months or years later, this is the first major paper to show it can produce successful results when performed concurrently with below-knee amputation, Valerio said.

TMR involves transferring transected peripheral nerves of an amputated limb to motor nerves of residual muscle. Attaching cut nerve endings to nerves in a nearby muscle helps re-establish neural circuitry and “gives the peripheral nerve somewhere to go and something to do,” Valerio told MedPage Today.

Targeted reinnervation originally was developed in 2002 to allow patients better control of prosthetics; that it also improved post-amputation pain was a later, incidental finding. The technique differs considerably from the traction neurectomy often performed in below-knee amputations in which “you would pull the nerve, cut it, and let it retract into the limb, then cover it while you close the amputation stump,” Valerio explained. With conventional neurectomy methods, up to 25% of patients with major limb amputations can develop chronic localized pain from symptomatic neuromas, he noted.

Since 2015, Valerio and co-authors have performed 22 TMR surgeries on patients with below-knee amputations, including 18 primary TMR (performed concurrently with amputation) and 4 secondary (performed months or years later) procedures. Over a mean of 18 months post-surgery, no patient developed symptomatic neuromas. In the primary TMR cohort, 72% reported phantom limb pain in the first month; this dropped to 19% at 3 months and 13% at 6 months — a substantial difference from other reported long-term phantom limb pain rates, which range up to 80%.

TMR patients who experienced phantom limb pain also reported lower pain scores and used less pain medication than patients who did not have the procedure, Valerio added.

“Targeted muscle reinnervation completely reshapes everything we thought we knew about nerve endings,” said Gregory Dumanian, MD, of Northwestern University’s Feinberg School of Medicine in Chicago, who recently led a randomized clinical trial which showed that secondary TMR improved phantom limb pain.

“TMR can revolutionize treatment for the limb pain that affects and often debilitates millions of amputees around the world,” Dumanian told MedPage Today. “There are low barriers to adoption. The ability to perform TMR is everywhere, but surgeons just need to know how to do the procedure.”

Why TMR reduces pain is not clear. It may be because the technique “has the advantage of preservation of longer peripheral nerve length than traditional traction neurectomy, permits rapid nerve ingrowth and reinnervation of target muscle, and potentially permits greater neuroplasticity to possibly alter the pain circuits and central pain upregulation,” Valerio and co-authors hypothesized. Their paper provides a surgical description of primary TMR in below-knee amputations in detail.

last updated 12.27.2018