An interbody fusion cage having a generally symmetric, annular cage body surrounding a central void extending from a lower surface to an upper surface in which to retain graft material in contact with adjacent vertebra. A lateral channel extending into each half from the cage perimeter contains a worm drive screw. One or more longitudinal channels extending from the upper surface to the lower surface intersect each lateral channel and house a pin which is provided with a series of helically cut worm gear teeth on its external surface for engaging the worm drive screw. The pins are simultaneously externally threaded and engaged to the cooperatively threaded internal surface of the longitudinal channel such that rotation of the drive screw by the surgeon after implantation causes the pins to rotate with the longitudinal channel and advance into the adjacent bone.