This paper presents a three-dimensional design of a compliant mechanism as a transmission system for its application in a novel human sternum prosthesis. The proposed compliant mechanism design is able to generate a coordinated movement between ribs during the respiratory process in human beings. Finite Element Method (FEM) analysis was performed in order to describe maximum stress values from the deformed elements of the mechanism by applying input forces. FEM results show that the compliant mechanism movements are proper for sternum prosthesis application, also it was possible to prove that maximum stress values generated in the mechanism, did not exceed the yield point of the material. Finally, by performing a fatigue analysis of the mechanism, it was possible to determine the maximum number of cycles that it can resist. Obtained results will be used to develop a complete design of the compliant mechanism and the sternum prosthesis in a prototype solution.