The aim of this study is to evaluate the in vivo kinematics of TKA performed with two different prosthesis: a kinematic retaining (Physica KR) and a posterior-stabilized (Physica PS) design by means of fluoroscopic analysis during activities of daily living (rising from a chair, stairs climbing, leg extension). In comparison with asymptomatic knee. Patterns of femoral rollback will be analyzed to assess if they are motor-task dependent and correlated with clinical outcomes.