various embodiments of intervertebral arthrodesis devices for insertion in an intervertebral space separating opposite faces of two adjacent vertebrae are disclosed . in one embodiment , the device has a ring shaped intervertebral cage having a bar that extends perpendicular to the axis of the spine , the bar has a height less than the rest of the cage , and a surface of the cage contacting the vertebrae has an undulating shape for limiting sliding of the cage in a plane parallel to the vertebrae faces .