The present invention provides a bone screw which can be used for fixation and/or fastening of prosthetic devices or instruments to bone tissue whose structure or dimensions differ from one region to another. In particular, the present invention provides a bone screw which is designed to optimize purchase in both the cancellous and cortical regions of a vertebral body. In an exemplary embodiment, the bone screw has a distal portion and a proximal portion in which the diameter of the thread on the proximal portion of the screw is greater than the diameter of the thread on the distal portion of the screw.
