A needle used in in-vivo medical percutaneous procedures is subject to auto-deflection coming from its interactions with inhomogeneous and anisotropic tissues and organs in human body. In this paper we present the modelling and the characterization of microsensors glued on a medical needle in order to detect its real-time deflection by measuring strain variations on the needle. A first prototype has been developed by gluing metal foil strain gauges to the surface of a biopsy needle. The characterization of this prototype is carried out in comparison with theoretical analysis and finite element method (FEM) modelling. Results acquired through these different methods show an excellent conformity and confirm the feasibility of an instrumented medical device.