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Page 8 of 15 Gunderson et al. Plast Aesthet Res 2023;10:50 https://dx.doi.org/10.20517/2347-9264.2023.42

of the tarsal joint varied from animal to animal, as demonstrated in Figure 2.

Morphological examination of the nerves distal to the carpal and tarsal joints
The morphological analysis revealed that the average cross-sectional sample contained a rounded average of
10 fascicles within the extracellular matrix. The median number of fascicles was found to be 8 across all
2
2
samples. The average fascicular area across all samples was 283,108.35 µM . At 846,645.3 µM , samples of the
lateral plantar nerve taken 1cm proximal of the crease of the ankle had the largest average fascicular area.
The proximal and distal samples of this nerve had 16 and 13 fascicles, respectively. On average, the
fascicular area constituted 15.23% of the total nerve area. The nerve with the greatest fascicular area was the
proximal bifurcation of the lateral plantar nerve, constituting 39.43% of the total nerve area. Detailed results
of morphological neural analysis can be found in Table 3. Histological cross-sections of a sample of nerves
are demonstrated in Figure 3.

Surgical approach for creation of ONI ovine model
A cadaveric sheep forelimb was utilized for demonstration. A nine-centimeter lazy-S incision was created
over the proximal dorsal metacarpal. Dissection of loose areolar tissue revealed the primary interdigital
sensory nerves in this area, representing the branches of the Superficial Radial Nerve. As demonstrated in
our anatomic data, there is more variation in branching patterns of some nerves rather than others, as well
as more variation in nerve circumference of some nerves over others. It was found that the Central Branch
is often the thickest with the least variation; thus, the Central Branch was chosen as our target nerve for
creating a reproducible sensory neural interface in sheep. Target nerve was transected distally, three
centimeters from the carpal joint. Soft tissue overlying the bone was cleared using a hemostat and elevator.
A primary corticotomy was made 20 mm distal to the carpal joint on the medial side of the bone with a
handheld electric drill, using a 3/16th inch (4.76 mm) drill bit. A secondary, smaller corticotomy was made
with a 5/32nd inch (3.97 mm) drill bit 1cm lateral to the primary corticotomy. Nerve circumference data
were used to inform the correct choice of size for the cuff electrodes, as well as drill size for the corticotomy.

A neural interface consisting of three spiral silicone cuffs [Figure 4A-Figure C], two of which contain active
electrodes [Figure 4A and Figure 4B] for stimulation and recording, and a third with no electrodes that
serve to stabilize the interface [Figure 4C], was created as previously described . Spiral nerve cuff
[14]
electrodes were used based on availability and applicability, but a range of interfaces are applicable.

Electrode A was attached to the distal end of the transected target nerve. Electrode B was then connected
more proximally to the nerve, at a point of minimal tension. The target nerve, concurrently with Electrode
A, was then transposed into the medullary canal through the primary corticotomy by threading an
epineurial propene suture into the primary corticotomy and out the secondary corticotomy and secured to
the periosteum. Electrode B remained outside the medullary canal, maintaining the separation of 10cm
necessary for stimulation and recording of compound nerve action potentials between electrodes. The distal
electrode (A) can then deliver sensory stimulation to be detected by the proximal electrode (B) in situ. The
electrode cables then exit transcutaneously and are anchored with suture.

DISCUSSION
The Osseointegrated Neural Interface is a developing technology with an overarching goal of creating a
[12]
bidirectional prosthesis capable of both motor control and sensory realization . This technology has
demonstrated success in a small animal model involving rabbits, but longitudinal studies in a large animal
model are necessary before translation to human use can be pursued . Building on current clinically
[3,4]
translatable ovine models for osseointegration, we studied the topography of ovine nerves distal to the