Bone stress injuries are prevalent among athletes and military recruits and can significantly compromise training schedules. The development of an ankle–foot orthosis to reduce tibial load and enable a faster return to activity will require new device testing methodologies capable of capturing the contribution of muscular force on tibial strain. Thus, an actuated robotic surrogate leg was developed to explore how tibial strain changes with different ankle–foot orthosis conditions. The purpose of this work was to assess the reliability, scalability, and behavior of the surrogate. A dual actuation system consisting of a Bowden cable and a vertical load applied to the femur via a material testing system, replicated the action-reaction of the Achilles-soleus complex. Maximum and minimum principal strain, maximum shear strain, and axial strain were measured by instrumented strain gauges at five locations on the tibia. Strains were highly repeatable across tests but did not consistently match in vivo data when scaled. However, the stiffness of the ankle–foot orthosis strut did not systematically affect tibial load, which is consistent with in vivo findings. Future work will involve improving the scalability of the results to match in vivo data and using the surrogate to inform exoskeletal designs for bone stress injuries.

Introduction: In prolonged care scenarios, where medical evacuations are significantly delayed, the treatment and transport of casualties with extremity musculoskeletal injuries will drain combat units’ human resources. Developing enhanced splinting techniques to restore casualty mobility and function can alleviate this drain. To guide this development, a panel of tactical combat and wilderness medicine experts was assembled to determine which extremity musculoskeletal injuries had the greatest impact on unit capabilities, and the materials available for splinting these injuries. Information Gathering: Unstructured consultations with panel members yielded preliminary lists of injuries and materials. These lists were consolidated and redistributed to panel members for final evaluation where they ranked the injuries based on frequency and human resource cost and assessed the accessibility of materials. Responses for the final evaluation were statistically analyzed using Wilcoxon rank-sum tests and Placket Luce models. Lessons Learned: Aggregated responses indicated that panel members thought that knee and ankle ligamentous injuries and radial head fractures were the most frequently occurring injuries, although closed distal femoral fractures, below knee amputations, and open tibia fractures would require the most demand for injury care. Assessing the combined impact of frequency and human resource cost indicated that knee and ankle ligamentous injuries and closed tibia fractures had the greatest impact on unit readiness. Responses also indicated that a variety of materials would be available for applying or improvising splints. Conclusion: Although the combined impact of knee and ankle ligamentous injuries were ranked the highest, limitations in relative rankings and the existence of effective low-cost treatments for these injuries suggest that greater gains in unit effectiveness would come from focusing on developing solutions for fractures with higher human resource cost, such as leg and arm fractures. This information can be used to develop enhanced splints that can preserve unit readiness in the field.

This investigation seeks to understand how the interfaces between fracture orthoses and the body affect the relative motion between the user and device. Excessive relative motion can inadvertently load the fracture and prevent healing. Identifying interfaces that minimize relative motion will inform the designs of future fracture orthoses. Three types of interfaces are used to off-load the injured limb: a thigh corset, a sling that loaded the ischium, and a sling that loaded the patellar tendon. However, little is known how these interfaces interact or with one another. Eighteen able-bodied participants were fitted with an adjustable interface testing system (ITS) that redirected loads away from the foot and lower leg to more proximal parts of the body using different combinations of the three interfaces. A video motion capture system measured the relative motion between the ITS and the participants while varying the type of interface, load through the ITS, and tightness of the thigh corset. Average relative motion varied from 1.6 to 6.5 cm across all conditions. The thigh corset combined with either the ischial sling or patellar tendon-bearing sling allowed the least relative motion of the interface conditions tested. However, the combinations differ in the sagittal profile they create for the user as well as the breadth of injuries they can treat. All these factors need to be considered in the design of future fracture orthoses.