Abstract: The apparatus is designed for the installation of front and rear crossed prosthetic ligaments in the articulation of the knee, and includes a stem which extends, at one end, with an arc-like tapered portion the end whereof is adapted to be inserted through the surgical opening at the knee, to pass between the tibial plate and the condyloid cavity and to be positioned in the exact outlet position of the bore to be provided, a small block having at least one hole for a screw for fastening to the bone and a seat for coupling to a spherical joint, an arm which ends at one end with the spherical joint coupled to the seat, bears at the other end a clamp with a groove and countergroove for its longitudinal sliding and locking along the stem and has coupling elements for interchangeable bushes for guiding the drilling tool.