Measuring structural dynamic properties of human tibia by modal testing

Identifying structural dynamic properties of human bones seems to be a promising technique in diagnosing metabolic bone diseases such as osteoporosis and in monitoring fracture healing. The major aim of this work is to observe the changes in the "loss factor" of human tibia with decreasing mineral density which is known as the main indicator of osteoporosis. In this preliminary stage of the study, the experiments are carried out in vitro, on tibia specimens obtained from fresh-frozen cadavers, as well as on dry tibia. The specimens that are placed on a soft rubber to have free-free boundary conditions are excited by an impact hammer and the response is measured using an accelerometer. The measured frequency response functions (FRFs) are analyzed using modal identification techniques to extract the modal parameters of the human tibia. It is observed that the regenerated FRFs from the modal model closely match with the experimentally measured ones, which is also an indication of the linear dynamic behavior of human tibia. Comparison of the modal parameters from fresh-frozen tibia with those obtained from dry tibia indicates that there is considerable change in the loss factor of tibia when it loses its mineral content and collagen. The results of a set of preliminary in vivo FRF measurements and the identified modal parameters are also presented in this study. It is concluded in this work that the modal loss factors identified from in vivo FRF measurements can be a good alternative in diagnosing progressing osteoporosis.