Page 99 - JSOM Fall 2023

FIGURE 5. Off-loading orthoses – Examples of
different orthotic interventions that unweight
limb segments: (A) the thermoplastic fracture
orthosis stabilizes a closed tibia fracture through
circumferential pressure around the shank while
unweighting the limb via the articulated foot
section; (B) the patellar tendon bearing or axial resist
ankle–foot orthosis is designed to unweight (but
not stabilize) the fracture site transferring the load
to unimpaired tissues in the proximal shank; (C)
the Intrepid Dynamic Exoskeletal Orthosis enables
running while off-loading the distal shank; (D) an
Ischial Weight Bearing Knee–Ankle–Foot Orthosis
has a shelf on the proximal thigh section that allows
for weight transfer through the device and around
the entire limb to the ischial tuberosity of the
pelvis. Primary disadvantages to their use in austere
environments involve limited portability due to being
custom made in fixed and specialized facilities.

temporarily stabilize the fracture site locally in an internal utilization of an exoskeleton-like device to facilitate mechan-
fashion with respect to the mechanical and/or biological mi- ical off-loading), it would greatly expand the technical op-
croenvironment. This concept, however, is fraught with chal- tions currently available to develop a soft polymeric material,
lenges related to the environment being resource poor (e.g., such as highly tunable synthetic and/or biologic hydrogels.
lack of sterile surgical fields), and the nature of the tactical Hydrogels are routinely used within the field of regenerative
combat and wilderness injuries (e.g., open fractures), which medicine to mediate the local delivery of bioactive payloads
are characterized by concomitant soft tissue injuries and high at clinically relevant concentrations over a prolonged period
levels of contamination. As such, existing clinical practice of time relative to systemic delivery. As such, they represent
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guidelines for management of these wounds would advise a unique platform technology to facilitate the spatiotempo-
against primary closure and/or placement of foreign bodies, rally controlled release of antibiotics and/or growth factors
such as internal fixation devices, as each would increase the needed to control infection, accelerate healing, and/or dampen
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likelihood of infection. Thus, to achieve success in utilizing a pathologic wound repair processes. To that end, one promis-
biomaterial approach for fracture stabilization within a PCC ing report by Johnson et al. describes an injectable polyeth-
environment, design criteria need to exhibit characteristics tra- ylene-glycol-based hydrogel that adheres to fracture surfaces
ditionally thought to be inversely related to each other. For and delivers an antimicrobial enzyme over the course of 24
example, the materiel solution would need to be sufficiently hours to control infection and support fracture repair. While
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porous and/or degradable to allow for the ability to deliver this study likely does not represent a permanent solution for
clinically relevant antibiotic payloads, while also supplying PCC fracture care, it does represent the type of approach that
sufficient mechanical stability to support weight bearing. As could be a viable solution. In other words, it embodies the
such, this is a challenging area, and our thorough literature re- idea that early treatment of the unique sequela of battlefield
view did not identify any currently available materiel solution fractures is paramount for optimization of subsequent fracture
that could meet all the necessary requirements. healing outcomes, and represents another starting point for
iterative improvements (e.g., targeting of endogenous stem cell
The Defense Advanced Research Projects Agency (DARPA), populations). Continued investment toward the development
however, did solicit proposals in 2008 to develop a “fracture of an optimized biomaterial approach for local fracture stabi-
putty” to facilitate healing of segmental fractures. While the lization within an austere environment is therefore warranted.
DARPA funding call did not explicitly require the consider- Biomaterial advances in conjunction with an exoskeleton will
ation of a PCC operational environment in its design crite- likely facilitate temporary, in field, return to duty of injured
ria, it was envisioned that such materials would preferentially Servicemembers when evacuation to higher echelons of care
bind to bone and allow full weight bearing within seven is delayed.
days. Moreover, it was envisioned that the resultant materiel
product would be fully degradable, non-toxic, non-antigenic, Conclusion
and serve to deliver bioactive payloads (e.g., osteo-inductive
agents and/or antibiotics) where appropriate, to create an The likelihood that U.S. Forces will not have air superiority in
optimal mechanical environment for bone ingrowth. In ad- future conflict highlights a need for developing novel/next gen-
dition, the materiel product would also theoretically be low eration materiel solutions that allow for mobility after incur-
pack volume and easy to use. While these efforts have not yet ring a lower extremity fracture during a PCC scenario. Austere
delivered a fielded materiel solution, the concepts laid out by environments, and the consequent delayed evacuation times,
DARPA may represent an ideal starting point for PCC-focused prevent the ability to surgically stabilize these fractures. Liter-
interventions. ature continues to support the use of splinting after a fracture
as a prehospital intervention to reduce pain, protect soft tissue
Alternatively, if the load bearing requirement of a putative structures of the injured limb, and provide traction (when trac-
fracture putty was removed (e.g., due to the combinatorial tion is indicated).

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