A system and method of securing an intervertebral fusion cage within the intervertebral space between adjacent vertebra in which one or more slots are provided in an anterior surface of the cage each extending from an oversized aperture. A retention plate having a post and enlarged head is advanced into each slot via the oversized aperture and captured therein. The post is advanced to the terminal end of the plate and secured to vertebral body at its distal end by a bone screw. A locking clip is slideably positioned on the retention plate to prevent withdrawal of the bone screw. The slots preferably extend to margins of the anterior surface of the cage in, for example, the pattern of an “X” or an “H”. Sliding of the posts in the slots prevents the system from carrying the vertebral load (load shielding) and permits reduction in the intervertebral space to promote bone growth and fusion by graft material retained in the spacer.