Instrumentation for implanting an intervertebral disc replacement device includes a retaining device comprising a threaded attachment member for threaded engagement with the at least one mounting screw hole in the flange of the intervertebral disc replacement device, and a head flange extending from the threaded attachment member, wherein a portion of the head flange is in part abuttingly received against a side of the flange of the intervertebral disc replacement device and another portion of the head flange is partially received over a portion of the bone screw to prevent the bone screw from backing out of the at least one bone screw hole when the retaining device is fully engaged with the intervertebral disc replacement device. The invention also comprises a method of preventing a bone screw from backing out of a bone screw hole in an intervertebral disc replacement device, comprising the steps of inserting a retaining device into a mounting hole in the intervertebral disc replacement device and tightening the retaining device in the mounting hole such that a portion of a head flange of the retaining device becomes flatter against a portion of the intervertebral disc replacement device and another portion of the head flange of the retaining device abuts against a portion of the bone screw.