The objective of this study was the development of a numeric model of the human bony thorax, considering especially age related geometric factors. This model should represent both the male and female population aged 64 years and beyond. It should also enable the simulation of injury mechanisms adjusted for this age group. Initially, the present study identifies a whole series of geometric parameters that change with advancing age, based on 146 post mortem and 40 clinical computed tomography image series. It evaluates rib angles in relation to the surrounding space and within the rib cage, presents a detailed caption of parameters of a single rib (cross sectional area, curvature, longitudinal twist), parameters of the spine as a whole (scoliosis, kyphosis, rotation) as well as single vertebrae and the sternum. Furthermore, this study investigates the basic measures of the whole thorax (thorax depth and width). The age dependent differences found served as input parameters in order to morph nine young and old finite element thorax models, based on the human model THUMS 3. Here, average and extreme measurements were implemented. The results show several parameters that change significantly with advancing age. The most important are an increasing thorax depth and width and curvature of the sixth and seventh rib and a significant change of rib angles. Moreover, the spine becomes more kyphotic and the sternum more flexed in the sagittal plane. The human models THUMS 3, THUMS 4 and HUMOS 2 can neither be classified typically old nor young. The finite element simulations, run on basis of the geometric input parameters, present a significant influence of the increasing thorax depth with advancing age on the posterior force on the contact face of the ribs as well as on the stress distribution along the ribs. Against expectations, an increased thorax depth seems to have a protective effect and dominates other factors like differing rib angles. A human model which represents the 75th percentile of the old population was classified to be significant regarding changing geometry with advancing age. The geometry of a 75th percentile thorax of the old population was implemented into a THUMS 3 human model and validated. The study proposes the use of this model for future assessments of safety systems. (Author/publisher)
Samenvatting