System for determining the quality of a bone structure of a subject, particularly the porosity of a bone structure, said system comprising: - a body (10; 40) adapted for drilling into the bone structure and presenting an outside surface, - at least one first electrode having a contact surface arranged on the outside surface of the body (10; 40) so as to come into contact with the bone structure during drilling, - at least one second electrode having a contact surface arranged on the outside surface of the body (10; 40) so as to come into contact with the bone structure at a distance from the first electrode during drilling, - an electric generator adapted for applying an electric current between the contact surfaces of the first and second electrodes for a determined period of time, said electric current having a characteristic chosen from among a voltage and an intensity which is known, - a measuring device adapted for continuously measuring over the determined period of time the other characteristic chosen from among the voltage and the intensity of the electric current passing through the bone structure between the contact surfaces of the first and second electrodes, - a processing device adapted for continuously determining over the determined period of time an electrical magnitude representative of the capacity of the bone structure for allowing the passage of the electric current between the contact surfaces of the first and second electrodes, based on the known characteristic and on the measured characteristic, and for continuously delivering over the determined period of time a signal representative of the quality of the bone structure, particularly of the porosity of the bone structure, between the contact surfaces of the first and second electrodes, based on the determined electrical magnitude, characterized in that the processing device is adapted for continuously calculating a value for the electrical magnitude during the determined period of time, and for continuously associating during the determined period of time the value calculated for the electrical magnitude with a value for the quality of the bone structure, particularly for the porosity of the bone structure. - a body (10; 40) adapted for drilling into the bone structure and presenting an outside surface, - at least one first electrode having a contact surface arranged on the outside surface of the body (10; 40) so as to come into contact with the bone structure during drilling, - at least one second electrode having a contact surface arranged on the outside surface of the body (10; 40) so as to come into contact with the bone structure at a distance from the first electrode during drilling, - an electric generator adapted for applying an electric current between the contact surfaces of the first and second electrodes for a determined period of time, said electric current having a characteristic chosen from among a voltage and an intensity which is known, - a measuring device adapted for continuously measuring over the determined period of time the other characteristic chosen from among the voltage and the intensity of the electric current passing through the bone structure between the contact surfaces of the first and second electrodes, - a processing device adapted for continuously determining over the determined period of time an electrical magnitude representative of the capacity of the bone structure for allowing the passage of the electric current between the contact surfaces of the first and second electrodes, based on the known characteristic and on the measured characteristic, and for continuously delivering over the determined period of time a signal representative of the quality of the bone structure, particularly of the porosity of the bone structure, between the contact surfaces of the first and second electrodes, based on the determined electrical magnitude,