Abstract: The screw (1) comprises an end formed by a dog point (2) having a plane transverse surface (3) and a cylindrical lateral surface (4) connected to the plane surface (3) by a rounded annular radius (5), it also comprises a threaded part (6) contiguous with the dog point (2) in which a self-tapping zone (8) is made which terminates at the base of the dog point (2), a smooth cylindrical part (9) being moreover arranged between its threaded part (6) and its head (11). The smooth part (9) is connected to the head (11) by an inclined plane zone (12). The rounded dog point (2) makes it possible to hold back without harming any mucosa or aponeurosis situated behind a bone through which the screw passes. The smooth parts (9 and 12) avoid damage to the skin of the patient. This screw is intended to be positioned very precisely and to remain anchored in the patient for the whole time necessary for the planned investigations, which avoids repeated piercing of the cranium or of any bone at each examination.