Experimental Modal Analysis of an In-situ Clavicle

Clavicle fractures are widespread, and the understanding of their mechanism of occurrence via dynamic loading is important for prevention and design of protection systems. The proposed work will find the natural frequencies and mode shapes of the human clavicles in-situ, by employing experimental modal analysis (EMA) techniques on cadaver clavicles. The clavicle response to impact depends on mechanical energy transmission to the bone and requires an understanding of bone modal characteristics (natural frequencies and mode shapes), as well as the frequency content of the impact force. These dynamic forces include blunt trauma (sport injury or gun stock impact) or falls (i.e. motorcycle accidents) and exhibit a wide frequency spectrum. Clavicle modes are not well understood, and while researchers performed whole body or individual clavicle EMA, no in-situ EMA has been reported. Since an in-situ clavicle features its natural boundary conditions, mode estimation via EMA was more accurate than one performed for an isolated clavicle. The clavicle EMA used instrumented excitation sources (i.e. impact hammer) and sensors (i.e. triaxial accelerometers). The accelerometer responses gathered at several locations along the cadaver clavicle bone and the exciting force was recorded and through time-frequency transformations, the natural frequencies and mode shapes were identified. Mode shape visualization was performed in ModalView software. While material properties of cadaver clavicles may be influenced by embalming, the results, which include natural frequencies, modes and damping constants, would be more relevant than those obtained for isolated clavicles. These results would be used to design protection systems, define global material properties, and calibrate existing analytical models.