Devices that monitor penetration of an instrument in an anatomical structure

1. A device that monitors penetration of a penetration instrument in an anatomical structure having at least two zones of different impedances comprising:

a penetration instrument adapted to form a hole into said anatomical structure having said at least two zones of different impedances, the penetration instrument extending along a longitudinal axis between opposed proximal and distal ends. the penetration instrument having a surface including a cylindrical lateral surface extending from the proximal end, and a frustoconical distal surface at the distal end, the cylindrical lateral surface having a diameter measured transversally with respect to the longitudinal axis;

at least two electrodes located on the penetration instrument, each of the at least two electrodes having a contact surface coinciding with the surface of the penetration instrument, wherein the at least two electrodes comprise at least one first electrode having the contact surface coinciding with the distal surface of the penetration instrument, and at least two second electrodes having the respective contact surfaces coinciding with the lateral surface of the penetration instrument, wherein the contact surface of each second electrode is annular, the second electrodes forming longitudinally spaced annular contacts;

a source of current adapted to supply the first and second electrodes;

an impedance measuring device adapted to measure the impedance between the first and second electrodes during penetration of the penetration instrument into said anatomical structure;

a signalling device adapted to produce a signal at a time a variation in impedance is detected by the impedance measuring device when the penetration instrument passes from a first of said zones having a first impedance to a second of said zones having a second impedance to inform in real time a practitioner of the position of the penetration instrument;

wherein the contact surfaces of the first and second electrodes are dimensioned to be constant as a function of a degree of penetration of the penetration instrument in the anatomical structure, said contact surfaces having a dimension measured from the proximal end to the distal end of the penetration instrument along the longitudinal axis that is smaller than the diameter of the cylindrical lateral surface.

2. The device according to claim 1 , wherein the at least two electrodes comprise at least two first electrodes that are coaxially arranged and separated from each other by insulation.

3. The device according to claim 1 , wherein the at least two electrodes comprise at least two first electrodes that are symmetrical with respect to the longitudinal axis of the penetration instrument.

4. The device according to claim 1 , wherein the at least two electrodes further comprise a third electrode partially covering the lateral surface of the penetration instrument.

5. The device according to claim 1 , wherein the signal is a sound signal, the signalling device being adapted to decrease a frequency and/or rhythm of the sound signal as a function of impedance measured.

6. The device according to claim 4 , wherein the signalling device is adapted to decrease the frequency and/or rhythm in a non-linear manner as a function of the impedance measured.

7. The device according to claim 1 , further comprising a central channel adapted for a passage of an additional instrument.