An expandable cage which is placed between the vertebrae, is moveable when preferred, closes the opening between the vertebrae upon being moved, and hence can be integrated in any intervertebral opening. The expandable cage has at least one body with at least one space and at least one rib； at least one moveable part which is located inside the body and has at least one bearing area, at least one base, and at least one nail, the moveable part being moved unilaterally by the balloon； at least one balloon which applies the force required to be applied on the base of the moveable part for ensuring unilateral movement of the moveable part； at least one hole through which the balloon can pass； and at least one compression element which supplies the required fluid to the balloon.
