Abstract: The invention relates to a self locked mechanical femoral prosthesis and the method for implanting same. The shank (5) of the prosthesis (1) is separated into two parts (7) and (7'), and includes a slit (f) in which is introduced a rack (6). The profile of this latter cooperates with the internal profile of the mobile part (7) so that when the rack 6, under the action of a screw (8), undergoes a vertical movement, it causes a lateral movement of the mobile part (7) that widens the shank (5) of the prosthesis ensuring locking thereof in the bone.