Lumbar and cervical interbody or intervertebral devices for implantation between adjacent vertebrae of a spine and/or within intermediary canals of long bones are characterized by a body defining a superior end and an inferior end whose surfaces have serrations or teeth thereon forming anti-backout structures that allow implantation of the body but inhibit removal or backing out therefrom. The one-way structures may extend from the anterior end to the posterior end. The one-way structures may take different shapes but are always configured to allow insertion of the interbody device in an anterior-first manner while preventing and/or inhibiting the interbody device from backing out posteriorly. The various interbody devices may be further characterized by a body defining a cavity that is in communication with the superior and inferior ends of the body and at least one lateral side thereof via openings in the body. Undercuts are formed in the body about the adjacent the openings in order to support bony ingrowth within the void.