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The goal of our paper is to quantify the electrical energy that can be harvested within a new generation of instrumented knee implant during normal walking. This generation of knee implant is proposed to assess the in vivo anteroposterior and mediolateral distributions of tibiofemoral force on the tibial baseplate without the need to be powered from an external source of energy. The proposed self-powered diagnostic knee implant can provide the clinicians with useful information on the sagittal and coronal instabilities of the prosthetic knee throughout its lifespan. Four piezoelectric elements were embedded within the anteromedial, posteromedial, anterolateral, and posterolateral compartments of the tibial baseplate. These elements can simultaneously be used to sense the force distribution and generate the electric power needed to supply the acquisition, processing, and transmission system located in the stem of the implant. In order to study the power generation issue, OrCAD/PSpice and MATLAB/Simulink models of the piezoelectric element have been developed to quantify the electrical energy harvested under operating conditions close to those encountered in vivo during normal walking. Furthermore, an experimental prototype of the self-powered diagnostic knee implant has been designed, developed, and tested in our laboratory (LaTIM, INSERM U650, Brest, France) in order to validate the modeling results.