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Eftekari et al. Plast Aesthet Res 2022;9:43 https://dx.doi.org/10.20517/2347-9264.2022.33 Page 9 of 13

In a retrospective review of 90 patients, RPNI surgery has shown a significant decrease in symptomatic
neuroma pain (0% vs. 13.3%) when done prophylactically at the time of amputation compared to simple
[28]
neuroma excision with burial in muscle . Moreover, these data also support an overall significant decrease
in phantom limb pain (51.1% vs. 91.1%) and post-operative complication rate (31.1% vs. 55.6%) at 1year
follow-up . Although RPNI surgery has shown positive results in both animal studies and clinical trials,
[28]
drawbacks of this approach include an increased operative time by 8-12 min per muscle graft, as well as the
possibility of hematoma formation at the muscle tissue harvest site . Further longitudinal studies will allow
[27]
for a more complete understanding of the long-term benefits and consequences RPNI may have for
symptomatic neuroma formation as well as control of neural prosthetics.

INTRAOSSEOUS TRANSPOSITION
Unlike the TMR and RPNI approaches, an intraosseous (IO) transposition relocates a transected nerve into
bone rather than muscle. This approach was first reported in 1943 when a transected nerve was buried into
the spongy bone and thus protected from external stimuli by the encasing bone . More recently, this
[32]
technique was again reported as a viable methodology for the treatment of symptomatic neuromas
transposing nerves into the medullary cavity of long bones . Creating a transposition into the medullary
[1]
cavity of a long bone instead of spongy bone affords a much larger and protected space for the residual
nerve and also allows for larger nerves to be transposed. This technique has also recently been shown as a
methodology for neural interfacing by utilizing an electrode interface on the residual nerve placed within
the medullary canal . This technology - the Osseointegrated Neural Interface (ONI) - provides a stable
[33]
platform that is bimodal, including the treatment and prevention of amputation pain and the creation of a
[33]
neural interface for prosthesis control [Figure 7] .
The IO transposition approach begins in the same fashion as the previous techniques, with isolation and
resection of the symptomatic neuroma and proximal transection of the involved nerve. Next, the underlying
bone is identified, and a cortical surface is cleared for creating a corticotomy. The nerve is then passed into
the canal and the perineurium is secured to the periosteum with a small diameter nylon suture before
closing the incision site [Figure 8].

Clinical studies of IO transposition into spongy bone without ONI have shown a 70% success rate in
[34]
patients with symptomatic neuromas of the hand . IO transpositions have also been used in patients with
hand neuromas who have failed their first attempt at surgical intervention, with a case report of 11 patients
[35]
reporting a success rate after repeat surgery in 10 of the patients with a mean follow-up of 25 months .
Although intraosseous transpositions have shown high rates of success in burying in bone, this approach
has been limited to use mainly within the hand and is not without complications. Common complications,
including missing branches of a transected nerve, and the possibility of the buried nerve being pulled out of
the bone and back into the environment, lead to exacerbation of symptoms and the need for repeat
surgery . Conversely, IO transposition into the medullary cavity of long bones has shown excellent results,
[35]
with two case studies involving a tibial nerve implanted into the tibia and a sciatic nerve implanted into the
femur showing complete resolution of the patients’ debilitating pain . However, this approach is novel and
[1]
has not been tested extensively in larger clinical trials. Further investigation of this method is needed to
better understand the long-term sequelae and recurrence of symptomatic neuroma formation.

IO transposition with ONI is currently in preclinical trials, with the first ONI completed involving a
rabbit for proof of concept and a follow-up study showing efficacy using a more complex sieve
[36]
electrode . Although this stable and more complex interface has shown promise, further animal studies are
[33]
needed to assess the efficacy of the IO transposition with ONI in creating stable, high-fidelity interfaces.