An expandable cage (1) for maintaining a distance between two vertebras on a spine and providing fusion is disclosed. The expandable cage (1) comprises a horizontal axis, a front part with an upper arm (1.1), a lower arm (1.2), and shaft fixation sockets (1.7.1 and 1.7.2) located between the arms (1.1 and 1.2), and a hollow shaft (2) with graft holes (2.4). The shaft (2) is placed parallel to the horizontal axis and partially inside the shaft fixation sockets (1.7.1 and 1.7.2). The cage (1) is expanded vertically by rotating the shaft (2) 90 degrees with an instrument, thus further separating vertically the upper arm (1.1) and the lower arm (1.2).
