Development of a Finite Element Model of the Human Shoulder

Abstract

Abstract During an automotive side impact, the shoulder is likely to be the first body part that is directly impacted either by the internal structures of the vehicle or by the side airbag. Therefore, a good understanding of the injury mechanism and the kinematics of the shoulder is critical for occupant protection in side impact. Existing side impact crash dummies do not have structures that are capable of reproducing the kinematics and kinetics of a human occupant. Over the past several years, many numerical models have been developed from head to foot in an attempt to overcome the shortcomings of these crash dummies. However, relatively few attempts have been made to include the shoulder. The purpose of this study is to develop a finite element model of the human shoulder in order to achieve a deeper understanding of the injury mechanism and the kinematics of the shoulder in side impacts. Basic anthropometric data used to develop the skeletal portion of the shoulder model were taken from a commercial data package of the human shoulder geometry (Viewpoint Datalabs). This geometry was scaled to fit a 50th percentile male occupant according to the data reported by Schneider et al. (1983). The shoulder model included the three bones of the shoulder, namely the humerus, scapula and clavicle. Each bone was modeled in two parts. The spongy bone was modeled using crushable solids and the cortical bone was modeled using damageable shell elements. The model also includes major ligaments, which form the acromioclavicular and sternoclavicular articulations. The deltoid muscle, which was modeled by crushable solids in order to absorb part of the impact energy, was added to this model for lateral impact simulations. This shoulder model was then integrated with a human thorax model developed by Wang (1995), along with other preexisting models of other parts of the human anatomy. Material properties for the model were taken from the literature. Experimental data obtained from lateral impact sled tests of 17 cadavers conducted at Wayne State University were used to validate the model. Impact forces in four regions, specifically, the shoulder, thorax, abdomen and pelvis, were calculated by the model and were compared with forces obtained experimentally from rigid wall impacts at 6.7m/s and padded wall impacts at 8.9m/s.