An interbody spacer for the spine is provided. The interbody spacer includes a cage and bone screws configured to anchor the cage between two vertebrae of the spine. The cage includes a screw plate configured to mate with the cage in a front-loading fashion. The screw plate is interchangeable with another screw plate configured to receive a different number of bone screws. For example, one screw plate adapted for three bone screws is interchangeable with another screw plate adapted for four bone screws and removably connected to the same cage. The screw plate is connectable intraoperatively or pre-assembled. Each screw plate is also provided with an anti-backout mechanism to retain the bone screws and prevent the bone screws from backing out with respect to the screw plate. The anti-backout mechanism includes a cover plate, locking screw or retaining ring.
