Among fall-related injuries, scaphoid fracture accounts for 60% of all carpal fractures. Many of these falls occur during daily life activities and can be avoided by establishing preventative interventions. Understanding the mechanical properties of palmar soft tissue is essential since it plays an important role in modulating the magnitude of the peak impact force. Coupling these characteristics with age, joint position and muscle activation can add a new level of biofidelity that will improve the accuracy of human models as well as the design of any technology that depends on quantified physical contact with the human hand (wearables, orthoses, or assistive devices). In this project, the in vivo characteristics of the palmar soft tissue at three hand positions and different muscle activation states (rested and activated) for two age groups (young individuals: 19-30 and older adults: 50+) at low (0.2Hz) and high (20Hz) frequencies were investigated and modelled. The derived parameters were incorporated into a forward fall simulation to determine the peak force and energy absorption. The captured palmar soft tissue properties were rate and depth dependent. Muscle activation state and age had greater effects on palmar soft tissue behavior compared to hand positioning. Therefore, to add accuracy to human models and simulations, it is important to involve those variables. Also, as fall scenarios can occur at different heights and velocities, capturing tissue behavior in a viscoelastic model that accounts for the effect of impact rates is important for the analysis of peak force during impact in fall simulations. The force applied to the hand for falls above 0.4m for older adults and 0.5m for young adults can cause a risk for wrist fracture based on our fall simulation. To expand the investigation of in vivo soft tissue characteristics on other parts of the body, a novel indentation system was developed. The precise measurement of in vivo soft tissue contact characteristics can be useful for designing injury prevention technologies and it may have the potential to be used to provide early detection of ulceration or disease. In summary, the palmar soft tissue properties are presented in this work by considering variables such as muscle activation and age. This could add biofidelity to fall simulations and human models, which provide the foundation for understanding injury mechanics.
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Thesis advisor: Sparrey, Carolyn
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