Abstract: A surgical instrument for the surgical operation of anterior fenestrated spondylodesis comprising an elongated hollow body with a handle at one end, and a detachable hollow cylindrical cutter with a cutting edge, at the other. Incorporated within the body is a shaft with a knife on the end situated within the cavity of the cutter. The instrument has a device for securing the shaft in the body in a position whereat the blades and cutting edge of the knife and the cutter lie in the same plane. The cutter is intended for excising two transplants in the shape of cylindrical segments from two adjacent vertebrae, and the knife, for undercutting them, once they are formed by the cutter.