Abstract: An interbody spinal fusion implant for insertion across a disc space between adjacent vertebral bodies of a human spine has a body two top side and two bottom side junctions, with at least a pair of diagonally opposed junctions having a distance therebetween that does not significantly exceed the implant body height. The implant also includes one or more bone penetrating protrusions extending outwardly from at least the upper and lower walls of the implant. The implant is inserted on its side between adjacent vertebral bodies and then rotated 90 degrees into place. The protrusions penetrate the endplates upon rotation, thereby securing the implant within the spine. The implant has at least one passage therethrough from the upper wall to the lower wall to promote fusion through the implant. Because of the specialized opposed junctions overdistraction between the adjacent vertebral bodies is avoided when the implant is rotated from an initial insertion position to a final deployed position.