Non-injurious and injurious impact response of the human shoulder three-dimensional analysis of kinematics and determination of injury threshold.

Seven Post Mortem Human Subjects were submitted to three low velocity impacts (v=1.5 m/s) to the right shoulder at three different angles in the horizontal plane (-15 degrees , 0 degrees , +15 degrees ). Then, the left shoulder was submitted to a purely lateral high velocity impact (v=3, 4, 6 m/s). The load was delivered by a 23.4 kg impactor fitted with a rigid rectangular impacting plate. Shoulder and thoracic bone structures were equipped with tri-axial accelerometers and photographic markers, whose trajectories were tracked in 3D by seven high-speed cameras. The results were scaled in order to account for the differences between the subjects' anthropometry and to define response corridors for the evaluation of the dummies' shoulders. Impact forces as well as several shoulder deflections were analyzed with respect to each subject's injury survey in order to find the most relevant parameters for the prediction of injuries. In the case of oblique impacts, slight modifications in the shoulder responses were observed, with higher force peaks obtained for the +15 degrees impacts in comparison to the 0 degrees and -15 degrees impacts. Acromion-to-sternum deflection peak values were closely linked with a clavicle fracture, but could not predict other types of fracture for which acromion-to-acromion deflection was a better predictor.