A spinal interbody fusion cage has a body whose anterior/posterior profile may be varied through angular positioning of one or more articulating segments of the body without changing the superior/inferior height of the body. The present spinal interbody fusion cage has N segments or sections wherein at least one segment is articulated relative to another segment via a connection point, pivot or pivot structure such that the anterior/posterior profile is variable through angular positioning of one or more of the segments. The pivot structure may be configured so as to allow unidirectional movement between the connecting segments thereby allowing articulation in one plane or to allow omni-directional movement between the connecting segments thereby allowing articulation in multiple planes. The various forms of the present interbody fusion cage include superior and inferior sides or bone abutment surfaces that have serrations, teeth or similar functioning structures (teeth). The teeth extend between the anterior end and the posterior end. The teeth may take different shapes but are configured to allow insertion of the spinal interbody fusion cage in an anterior-first manner while preventing and/or inhibiting the spinal interbody fusion cage from backing out posteriorly.