Regenerative Peripheral Nerve Interface (RPNI)
ICD-10-PCS root operation selection

What is this new procedure, where a free muscle graft is wrapped around a cut nerve ending, like a piece of sashimi around the end of a piece of spaghetti? The muscle graft doesn’t “do” anything active to the nerve, it just acts as a target for reinnervation by the nerve, so things stay organized and neuroma is less likely to form. This creates a challenge in choosing a PCS root operation.

So if you’re hungry for the PCS coding implications, read on!


A relatively new procedure, Regenerative Peripheral Nerve Interface (RPNI), is intended to reduce or eliminate neuroma formation by providing a free muscle graft as physiological target for peripheral nerve ingrowth. This procedure was originally designed for prosthetic control. RPNI would most commonly be done after an amputation, either at the same operative episode or afterwards if a neuroma formed.

An RPNI is a piece of grafted autologous muscle that regenerates and becomes reinnervated by an implanted residual peripheral nerve. RPNIs rival “Targeted Muscle reinnervation” for controlling myoelectric prostheses because RPNI electrodes are in direct contact with muscle instead of skin.

Post-above-knee amputation stump
A) nerve trunk exposed B) nerve fascicles separated C) free muscle grafts harvested
 muscle grafts wrapped over and sewn to the cut nerve endings

Regenerative Peripheral Nerve Interfaces for the Treatment of Postamputation Neuroma Pain
Woo SL1, et al. Section of Plastic Surgery, University of Michigan Health System, Ann Arbor, Mich.; and Department of Physical Medicine and Rehabilitation, University of Michigan Health System, Ann Arbor, Mich.

How do we code this in ICD-10-PCS?

Likely Root Operation choices include Repair, Transfer, Reposition, and Supplement.


Supplement is recommended as the root operation as the application of the free muscle graft augments the functioning of the nerve by allowing the nerve to re-innervate the muscle. In doing so, it inhibits neuroma formation. Though the muscle graft is the passive recipient of the innervation, it is its presence which confers the therapeutic benefit to the nerve by allowing the nerve to actively innervate it. In the case of RPNI for neuroma inhibition, therefore the muscle then has no other subsequent function.

Rejected PCS root operations include:
Reposition - because the nerve which is the recipient of the free muscle graft is not moved, or moved only incidentally, but nothing about the new location confers any therapeutic benefit to the nerve.

Transfer - since the cut nerve end is not taking over the function of another body part. The outcome in which the nerve re-innervates the small, free muscle graft does not create any functionality in the muscle graft or otherwise. The therapeutic benefit is enjoyed by the nerve itself.

Repair - as there is no restoration to normal function in either the nerve or the free muscle graft.

However, closely associated procedures done to reduce neuroma after amputation (often at the same time as RPNI), which involve attaching the cut end of the nerve to a different structure, for the identical outcome of avoiding neuroma formation, and which have a different root operation recommendation, include implantation of the cut nerve ending into:

Muscle in-situ = Reposition
Another nerve = Transfer

Example documentation:

“I then proceeded to harvest a tibialis anterior free muscle flap, a soleus free muscle flap, and a gastrocnemius free muscle flap. I planned to utilize each of these free muscle flaps for the purposes of creating a regenerative peripheral nerve interface. I started with the sural nerve. The cut end of the sural nerve was freshened. I utilized the tibialis anterior free muscle flap for creation of a regenerative peripheral nerve interface. The free muscle flap was approximately 3 cm in length by 1 cm wide x 0.5 cm thick. I utilized a 6-0 nylon suture to tack the tibialis anterior free muscle flap to the epineurium of the sural nerve. I then placed an additional epineurial suture at the cut end, tacking it to the central portion of the free muscle flap. I then folded the free muscle flap on itself and tacked the opposite end of the free muscle flap 180 degrees around the nerve to the epineurium. I then sewed muscle to muscle to complete the pocket. This effectively buried the sural nerve within the tibialis anterior free muscle flap. This created a good regenerative peripheral nerve interface. This will be allowed to indirectly revascularize over time.



Ed has been in healthcare his entire career with 15 years as a clinician and 11 years in a variety of HIM coding related roles. After 4 years as a respiratory therapist and 11 years as an emergency medicine Physician Assistant, the fascination with reading, analyzing, and translating medical documentation overcame his desire to perform patient care. For a guy who with a habit for reading the Encyclopedia Brittanica, the Merck Manual, and medical records just for fun, HIM became a natural fit.

Documentation and coding audits are firmly in Ed’s skillset but educating coders is what really makes him tick. He is known for effectively integrating anatomy, physiology, pathophysiology, medicine, and detailed procedural descriptions into his coding education in all forms.

He is a BS graduate in Biology from Virginia Commonwealth University and Master of Health Sciences from Duke University. Obsessed with aviation, he has a pilot’s license, 1000 skydives, owned an ultralight for several years, and currently designs, builds, and flies radio controlled airplanes and drones. Ed lives in Virginia with his wife and two kids, and plays outside with them as much as possible.


  1. Laura Capelo

    This is great information, what CPT codes are used to report these services?

    • kkluglein

      Hi Laura, This is difficult to answer without an operative report, but it’s likely that it’s an unlisted CPT 64999. It’s possible it could also qualify a modifier 22 if performed with another procedure that has a CPT code (i.e., neuroma excision).

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