Synthesis of Spatial Mechanisms to Model Human Joints

The role played by diarthrodial joint models in surgery, pre-surgical planning and prosthesis design has been widely recognized. This chapter presents a procedure for the modelling of the diarthrodial human joints. The procedure features three main sequential steps, each of them leading to the kinematic, kinetostatic and dynamic models of the joint respectively. In particular, the chapter focuses on the first model, which can replicate the joint passive motion, i.e. the joint motion under virtually unloaded conditions. This model proves to be of great relevance for a deeper understanding of the joint anatomical structures and is the basic step for the next two kinematic and dynamic models. The first model is represented by a spatial mechanism called equivalent mechanism. Special emphasis is devoted to the synthesis of the mechanism. Examples of knee, ankle, and lower limb modelling are reported that prove the potential of the procedure.