Patent ID: 8603172

Claim:
A cage configured to be interposed between a pair of vertebral bodies, comprising: a cage body; a left side surface and a right side surface formed in a left side and a right side of the cage body in a flat, smooth surface manner and parallel to each other; an upper surface and a lower surface formed in an upper side and a lower side of the cage body; and a plurality of projections arranged in a longitudinal direction and a lateral direction on the upper and lower surfaces of the cage body so as to protrude from the upper and lower surfaces of the cage body, wherein each of the plurality of projections protrude from the cage body in a direction perpendicular to the longitudinal direction and the lateral direction; wherein the plurality of projections include tip end surfaces that are arranged in the lateral direction to match with an arc curved surface formed around an axis in the longitudinal direction of the cage body, thereby forming a non-threaded leading edge and permitting insertion of the cage in between the vertebral bodies followed by rotation to a fixed position, wherein angles of inner end edges of the projections proximate to the left and the right side surfaces of the cage body along the arc curved surface are more acute than angles of inner edges of the projections positioned in between the projections proximate to the left and the right side surfaces, and wherein the projections have square cross-sectional shapes such that the projections are independent in the longitudinal and lateral directions.