An intervertebral spacer implant (80) is provided with a retention mechanism (86) to help alleviate expulsion and movement of the implant when placed in the spine while providing an implant that is easier to insert in the spine. In one embodiment the retention mechanism comprises a keel on at least one of the inferior or superior faces of the spacer implant preferably extending in an anterior-posterior direction. In another embodiment the implant comprises a spacer (84) and a plate (82), the plate comprising a supplemental or alternative retention mechanism. In one embodiment the retention mechanism comprises one or more holes (88) in the anterior end of the plate. In yet another embodiment, the retention mechanism comprises one or more blades that are in a first position when inserted and are preferably rotated to a second position that engages the superior and inferior vertebrae.