Targeted muscle reinnervation (TMR) for leg nerve pain

What TMR is

Every nerve cut during an amputation, or in an injury, sprouts new fibres. Without a target, these fibres tangle into a neuroma. In TMR, the surgeon divides the cut nerve, finds a nearby branch that supplies a muscle, and connects the cut nerve to that branch. The muscle acts as a target, and the nerve fibres regrow into it.^[1] TMR was introduced to help amputees control prosthetic limbs, and doctors noticed that these patients also had less pain.^[2]

Who might be considered

• People with a painful neuroma at the end of a residual limb, or phantom limb pain, after a lower-limb amputation. See residual limb neuroma pain and phantom limb pain.
• People having a planned amputation, when TMR can be done at the same operation to help prevent neuromas. See pain after leg amputation.
• Selected people with a painful neuroma of a limb that has not been amputated. Techniques for doing this in the lower limb have been described, but there is little evidence about how well it works.^[3]

What the studies show

• Randomized trial. Twenty-eight people with chronic pain after major limb amputation were assigned to TMR or the standard treatment of removing the neuroma and burying the nerve in muscle. At one year, the difference in phantom limb pain change was not statistically definite (adjusted P = 0.06), but a longitudinal analysis showed a significantly greater reduction in phantom limb pain with TMR. Residual limb pain trended in favour of TMR. At the longest follow-up, results favoured TMR.^[1]
• Lower-limb amputations. A systematic review of 11 studies (318 patients) found TMR effective in reducing phantom and residual limb pain with limited complications. The most commonly used donor nerve was the tibial nerve, and an average of about two nerve transfers were done per case. A neuroma developed after surgery in 7.2%.^[4]
• Pooled results. A systematic review of 14 TMR studies (366 patients), together with regenerative peripheral nerve interface studies, found improved neuroma pain in 75 to 100 percent of treated patients and phantom limb pain in 45% to 80%, with complications in 13% to 31%, most often slow wound healing. Only one study was a randomized trial.^[5]
• Compared with nerve removal. In a meta-analysis of neuroma surgery (1,150 neuromas), TMR gave good results in 82% of neuromas, performing better than neurectomy in a post hoc analysis.^[6]
• Timing. In a comparison of 105 limbs, a symptomatic neuroma came back in 19% of limbs where TMR was delayed until after a neuroma developed, versus 1% when TMR was done at the time of amputation.^[7]

What the operation involves

TMR is done in an operating room under anaesthesia. The surgeon finds the painful nerve, removes the neuroma if there is one, and connects the nerve end to a motor branch of a nearby muscle. If you wear a prosthesis, your prosthetist is part of the plan for recovery.

Recovery and expectations

• Pain may briefly increase at first. In a small study of 22 amputees who had TMR or a regenerative peripheral nerve interface, overall pain and pain medicine use decreased, but several people had more pain or needed more pain medicine in the first three months.^[8]
• Nerve fibres regrow slowly, so improvement can take months.
• Results vary, and TMR does not always remove all pain.

Risks

Risks include infection, wound-healing problems (the most common complication in reviews), bleeding, persistent or new neuroma pain, and the need for more surgery.^[5,4]

Is it right for you?

The right treatment depends on where the pain arises, how the nerve is arranged, your overall health and your goals. A nerve-focused evaluation, with imaging and diagnostic injections arranged with another specialist, helps decide. Other options are described in neuroma surgery options and regenerative peripheral nerve interface. Dr. Ozturk performs this procedure for appropriate patients, and an evaluation is how to find out whether it fits your situation.

When to seek care

Consider an evaluation if you have a tender, shocking spot in a residual limb or a scar, or pain in a missing limb that has not settled with treatment.