Apparatus for the fast angular orientation of a surgical instrument with respect to an implantation seat of a prosthesis in a patients bone, of the type comprising a moving sensor (16), which may be associated with said surgical instrument, and a fixes sensor (17), which may be integrally fastened to said bone during a surgical operation, said moving sensor (16) and said fixed sensor (17) being provided with position detection means and with signalling means of the detected position to a central memory and processing unit. Said central memory and processing unit comprises calibration means which detect the position of said moving sensor (16) when it is associated with a line passing through two known points of said bone and, simultaneously, they detect the position of said fixed sensor (17) when it is integrally fastened to said bone, and they record such position as initial work position.
