Objective: The human body changes as it becomes older. The automotive safety community has been interested in understanding the effect of age on restraint performance. Focus has been placed on characterizing the body's structural changes associated with age and gender. In this study, spine alignment and torso depth were assessed, because both variables have been shown to affect injury risk.
Methods: The data was obtained from computed tomography (CT) scans of more than 24,000 patients aged 16 and older. The data consisted of thoracic and lumbar vertebral angles relative to a fixed plane, as well as vertebra-to-front skin and spine-to-back skin distances. Angle measurements were taken in the sagittal plane at each vertebra level from T1 to L5; distance measurements were taken from T6 to L5. The data were analyzed as a function of gender and age with the young group defined as 16 to 29 years old and the older group as 75 and up.
Results: Vertebral angles were different depending on location. They varied from -24.5 ± 8.9° at T2 to 12.2 ± 5.6° at L1. The vertebral angles also varied with age. Angles in the older male group were 1.74 times larger at T1 and 2.03 times larger at T7 than in the young male group. Similar findings were observed for females. The effect of age and gender was modeled with forward/backward selection using a regression model. The vertebra-to-front skin distance also differed depending on vertebral level. It was highest at T10 at 162.5 ± 30.9 mm and lowest at L4 at 125.3 ± 37.3 mm for the entire study population. On average, males had larger distances than females. The spine-to-back distances were greatest in the lumbar area. The spine-to-back distance increased with lower vertebral level, regardless of age. The vertebral angle and distance data were analyzed for a male subgroup approximating the height and weight of a 50th percentile male dummy. The results showed that the vertebra-to-front skin distance increased with age. There was not a clear trend for the spine-to-back skin distance and L1 vertebral angle.
Conclusions: The changes in the vertebral angles, as well as the anterior and posterior spine-to-skin distances along the sagittal plane, were determined as a function of age and gender. The effect was greatest in the mid-thoracic area. Spine alignment and body shape differences need to be considered in human mathematical models used to develop safety countermeasures for the older population, because they may affect the loading path and lead to different seating postures or belt positioning. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.