During TKA surgery, a correct tibiofemoral alignment of the installed prosthesis can be effectively achieved by means of Computer-Assisted techniques. Unfortunately, the achievement of perfect ligament balance conditions still remains as unsolved problem. Any inaccuracy during the operation may degenerate and lead to prosthesis failure. Our aim is to develop an adaptive knee prosthesis, able to follow the physiological evolution of the body and, potentially, to modify its shape to fit the patient's morphological changes. In this paper, we focus on the actuation of the tibial component in order to compensate for collateral ligament imbalances. We face with severe constraints concerning the available volume, the high-accuracy level and system's solidity and biocompatibility. We discuss a model that we proposed in a previous work and we highlight its drawbacks. We consider then three possible approaches to realise the actuation: the use of a micromotor, the action of a magnetic field and the use of an external tool. After evaluating the pros and cons of each case, the micromotor approach is selected. We conclude by introducing an original design of adaptive tibial implant that we are currently developing.