Regenerative peripheral nerve interface (RPNI) surgery

What an RPNI is

When a nerve is cut, its fibres regrow. Without a target, they form a painful neuroma. The RPNI provides that target: an autologous free muscle graft (a small piece of your own muscle) is secured around the end of the transected nerve. The muscle graft gives the regenerating fibres something to reinnervate, which is thought to prevent neuroma formation.^[1]

RPNI is related to targeted muscle reinnervation. TMR connects a cut nerve to the motor nerve of a nearby muscle. RPNI wraps the nerve end in a separate muscle graft. Some surgeons combine the two. One technical report describes combining TMR with a pedicled, vascularized RPNI (vRPNI), which keeps the muscle’s own blood supply, with the aim of improving nerve regeneration. It presents a technique rather than outcome data.^[4]

Who might be considered

• People with a painful residual limb neuroma after lower-limb amputation. See residual limb neuroma pain.
• People having an amputation, when RPNIs can be created at the same time to help prevent neuromas. In studies where TMR or RPNI was done as prevention at the time of amputation, many patients reported no neuroma pain (48 to 100 percent) or no phantom limb pain (45% to 87%) at follow-up.^[3]

What the studies show

• Prospective lower-limb study. Twenty-two people with established chronic post-amputation pain had RPNI surgery for symptomatic neuromas. Over 12 months, residual limb pain improved significantly, phantom limb sensation improved significantly, and phantom limb pain fell modestly. Psychosocial measures improved, prosthesis use rose slightly, and no one lost function.^[2]
• Ultrasound comparison. In a retrospective study of 14 lower-limb amputees (7 with RPNI and 7 with traditional amputation), pain scores were significantly lower in the RPNI group, and ultrasound measured the neuromas objectively.^[5]
• Pooled review. A systematic review of three RPNI studies (75 patients) and 14 TMR studies found that these procedures improved neuroma pain in 75 to 100 percent of patients, with complication rates from 13% to 31%. Only one study overall was a randomized trial.^[3]
• Early recovery. In a small study of 22 amputees who had TMR or RPNI, several people had more pain in the first three months even though the overall trend was down.^[6]

What the operation involves

RPNI is done in an operating room under anaesthesia. The surgeon removes the neuroma, if one is present, takes a small piece of your own muscle, and wraps it around the trimmed end of the nerve. If you wear a prosthesis, your prosthetist is part of planning for recovery.

Risks

The risks are those of any limb operation: infection, wound-healing problems, bleeding, persistent or recurrent pain, and the need for more surgery. In pooled studies of TMR and RPNI, delayed wound healing was the most frequent complication.^[3]

How it compares with other options

Older, “passive” techniques such as removing a neuroma and covering or burying the nerve end still give positive results in a majority of patients treated. A review of the literature found no single standard of care, and surgeons choose among many techniques case by case.^[7] See neuroma surgery options for a comparison, and pain after leg amputation for the wider picture.

Is it right for you?

The decision depends on where your pain arises, the nerves involved, your health and your goals. 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 scar, or pain that limits your prosthesis or activity.