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Gunderson et al. Plast Aesthet Res 2023;10:50 https://dx.doi.org/10.20517/2347-9264.2023.42 Page 3 of 15

feedback based on the relative sheep models of osseointegration.

The purpose of this study is to elucidate the neural topography in the metatarsi and metacarpi of sheep
relative to the common amputation sites for osseointegration research in ungulates. The data obtained from
this anatomical study will then be utilized to develop a surgical design for creating an osseointegrated neural
interface in a clinically translatable sheep model, alongside similar anatomical studies in humans for direct
[12]
comparison .

METHODS
This work was not conducted with living animals or human subjects. No ethical approval was required.

Animals
Six pelvic and six thoracic cadaveric limbs from mature female, non-lactating sheep (mixed breeds: Polypay,
Tarhee, Dorset) were collected for anatomical study. Both forelimbs (thoracic) and hindlimbs (pelvic) were
obtained from previous studies, fresh frozen prior to dissection in a standard freezer at -20 ºC. No
embalming fluid was used for preservation.

Radiological evaluation of the metacarpal and metatarsal bones
Limbs disarticulated at the carpal and tarsal joints were imaged in pairs using a portable digital radiography
system (VetRocket, Santa Clara, CA, USA) including an Elkin EDR3 (Sound, Carlsbad, CA), Canon CXDI-
31 plate (Canon USA, Inc., Melville, NY, USA) and a min-X HF100/30+ generator (MinXray, Inc,
Northbrook, IL, USA). Each limb was radiographed in the medial-lateral transverse plane alongside a 10 cm
radiological scale bar. Measurements of metatarsal and metacarpal bones were made using the straightline
tool in ImageJ (NIH, Bethesda, MD), with the scale set according to the scale bar present in each image.
Horizontal measurements of the dorsal and palmar cortex bone thickness and medullary canal diameter
were made at the proximal, midpoint, and distal positions, as demonstrated in Figure 1. All measurements
were made in triplicate and averaged to limit human error. Vertical measurements of bone length were
made in the medial plane during microsurgical dissection measuring from the proximal point (carpal/tarsal
joint) to the distal point (MP joint), as these anatomic landmarks are more easily identifiable
intraoperatively relative to exposed nerves.

Microsurgical dissection of the nerves distal to the carpal and tarsal joints
Microsurgical dissection was performed by a single author (K.G.) with the assistance of other authors (W.Z.,
S.O., Z.N.) to determine the overall topography of the major nerves of the pelvic (superficial fibular, deep
fibular, and tibial) and thoracic limbs (superficial radial, dorsal ulnar, deep ulnar, and median) along the
metatarsi and metacarpi, respectively. The anatomical locations were selected for their relative positioning
to the common amputation site for osseointegration models in sheep, measuring and annotating branch
points of each nerve to determine viable interfacing targets for creating an ONI. Limbs were dissected using
clean, non-sterile microsurgery equipment (Roboz Surgical Instrument Company, MD, USA; Dumont
Switzerland, CH) with a Zeiss West Germany Universal Microscope (S3, 175348; NY, USA). Two
researchers were present at every dissection to ensure proper measurement recording and nerve
identification. Nerve circumferences were measured at three sites along the metatarsus or metacarpus: the
most proximal point (at the carpal/tarsal joint), the midpoint (halfway between the carpal/tarsal and
interphalangeal (IP) joints), and the most distal point (IP joint). Measurements were made by wrapping a
7-0 suture circumferentially around each nerve and subsequently measuring the suture. Each measurement
was made in triplicate and averaged to ensure accurate measurement and limit human error. Illustrations of
the variations in nerve branching patterns were made.