Sex-Based Differences in Calcaneal Injury Tolerances Under High-Rate Loading

• Main Author: Ceritano, Davide Walter
• Other Authors: Mechanical Engineering
• Format: Others
• Language: en
• Published: Virginia Tech 2020
• Subjects: underbody blast; ankle; calcaneus; fractures; sexual dimorphism
• Online Access: http://hdl.handle.net/10919/99103

In this experiment, average calcaneal fracture force is measured across male and female groups. The purpose of this experiment is an analysis of alternatives exploring the importance of sex-based criteria in models representing injuries typical in underbody blast environments. Seventeen (17) right legs were harvested at the knee from cadavers representing three anthropometries: 50th percentile male (6), 75th percentile female (6), and 5th percentile female (5). Care was taken to preserve anatomically correct geometry as the legs were cut to equal lengths, the tibia and fibula were potted in Dyna-Cast®, flesh and ligaments were excised from the inferior surface of the calcaneus, and a small Dyna-Cast® pad was poured and sanded flat – interfacing with the exposed calcaneal surface. Each test specimen was mounted in a custom fixture and exposed once to high-rate axial loading characterized by a constant acceleration and 25.4mm intrusion, achieving an average speed of 4.7m/s (σ = 0.3m/s) in 10ms. Input acceleration was measured by an Endevco 7264c accelerometer and a Denton 2513 six-axis load cell measured reaction force proximal to the specimen. A VR Phantom v9.1 camera recorded x-ray imagery at 2k frames per second. Data were collected by a TDAS Pro data acquisition system at 20k samples per second and filtered in accordance with SAE J211. Time of fracture, established through x-ray imagery, was used to determined fracture force from the electronically synchronized load-cell data. 100% injury was recorded. Average calcaneus fracture forces were reported as follows: 5406N (σ = 780N) for 50th percentile males, 4130N (σ = 1061N) for 75th percentile females, and 2873N (σ = 1293N) for 5th percentile females. Statistical significance was established between the reported averages according to three ANOVA tests: One-way (p = 0.0054), Brown-Forsythe (p = 0.0091), and Welch's (p = 0.0156). Unpaired Student's t-test confirmed significant differences between 50th percentile male vs 75th percentile female (p = 0.0469) and 50th percentile male vs 5th percentile female (p = 0.0030); the t-test did not show significance between the two female groups (p = 0.1315). Average impulse-to-fracture was calculated for each group and found to be not statistically significant. === Master of Science === A marked shift can be found in combat wound epidemiology towards a predominance of extremity injuries sustained from explosives. The Warrior Injury Assessment Mannequin (WIAMan) Project sought to develop a baseline dataset of post-mortem human surrogate responses to realistic explosive loading and correlate it to a highly instrumented mannequin for the further development of combat vehicles and personal protective gear. The following experiment exists within the WIAMan paradigm as an analysis of alternatives exploring the adequacy of the above mentioned baseline dataset in directly representing both male and female injuries. More specifically, this experiment interrogates the differences in average fracture forces between male and female calcanei across three anthropometries: 50th percentile male, 75th percentile female, and 5th percentile female. Testing was carried out on 17 right cadaver legs cut to equal lengths, potted proximally in Dyna-Cast®, with the inferior surface of their calcanei exposed; a small Dyna-Cast® pad was poured for each calcaneus and sanded flat. Each test specimen was fixed to a Denton 2513 six-axis load cell proximally and exposed to a high-rate, constant acceleration, 25.4mm displacement aligned with the calcaneus along the long axis of the leg bones. Fracture time, established through x-ray images recorded at 2k frames per second with a VR Phantom V9.1 camera, was used to determine load cell force measurement at fracture. Average calcaneus fracture forces were reported as follows: 5406N (σ = 780N) for 50th percentile males, 4130N (σ = 1061N) for 75th percentile females, and 2873N (σ = 1293N) for 5th percentile females. Statistical significance was established between the reported averages according to three ANOVA tests: One-way (p = 0.0054), Brown-Forsythe (p = 0.0091), and Welch's (p = 0.0156). Unpaired Student's t-test confirmed significant differences between 50th percentile male vs 75th percentile female (p = 0.0469) and 50th percentile male vs 5th percentile female (p = 0.0030); the t-test did not show significance between the two female groups (p = 0.1315). Average impulse-to-fracture was calculated for each group and found to be not statistically significant.