Total disc arthroplasty (TDA) is one of the most preferred surgical procedure instead of fusion in the treatment of a degenerated disc. In this study, the effects of changing position and core radius of an artificial disc prosthesis, placed in the C5-C6 functional spinal unit (FSU), on the range of motions (ROM) of the FSU was investigated via the finite element method. Firstly, three-dimensional CAD models of C5 and C6 vertebrae was obtained from a computerized tomography images of healthy male neck. Finite element model of a healthy C5-C6 FSU was created containing vertebrae, intervertebral discs, tissues and facet joints considering the normal anatomical features. In modelling of TDA method, the core radius of artificial prostheses was assumed as 4 mm, 6 mm and 8 mm, and their positions were changed to anterior, posterior and lateral according to their neutral positions. Finally, the effects of core radius and position changes of the prosthesis on the biomechanical properties of the FSU were investigated by the finite element simulations. It was found that the flexion and extension ROM of the implanted FSU was increased with changing the rotation center of the prosthesis from anterior to posterior and increasing the core radius from 4 to 8 mm. However, displacing the rotation center of the prosthesis in lateral direction did not change the ROM of the model for all motion types. (C) 2018 Karabuk University. Publishing services by Elsevier B.V.