A method of inserting a screw into a fusion cage, comprising the step of:i) attaching a screw head of a bone screw to a flexible bone screw driver comprising: a) a proximal handle,b) an intermediate shaft,c) a flexible distal end portion comprising a plurality of interlocking segments portion defining a periphery and a distal tip adapted to engage the screw head, andd) a flexible pre-bent sleeve that is configured to be placed radially over and around the plurality of interlocking segments to provide a loaded configuration,wherein the plurality of interlocking segments portion is substantially straight in its unloaded configuration,whereby the pre-bent sleeve pre-determines the trajectory of the tip in the loaded configuration,ii) inserting the bone screw into a threaded throughhole of a fusion cage comprising a front wall, a pair of opposing side walls, a back wall, and top and bottom surfaces adapted for gripping opposed vertebral endplates, wherein the front wall comprises the threaded throughhole,
