An intervertebral spacer having opposing plates seatable against opposing vertebral bones, separated by at least one convex element, preferably a radially slotted convex element having a wide end rigidly fixed to an upper plate and a narrow end rotatably mounted to a lower plate. The lower plate includes a central post extending upwardly from the inner surface of the lower plate, the post including a head that is received in a central opening in the narrow end of the convex element so that the convex element is allowed to rotate with respect to the lower plate so that the plates can rotate relative to one another.