System and methods for determining nerve direction to a surgical instrument

• US 8,147,421 B2
• Filed: 07/15/2005
• Issued: 04/03/2012
• Est. Priority Date: 01/15/2003
• Status: Active Grant

• Current Assignee: Nuvasive Incorporated
• Original Assignee: Nuvasive Incorporated
• Inventors: Farquhar, Allen, Gharib, James, Kaula, Norbert, Blewett, Jeffrey
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Pani, John
• Application Number:
  US11/182,545
• Publication Number:
  US 20070016097A1
• Time in Patent Office: 2,454 Days
• Field of Search: 600/117, 600/546, 600/554, 324512-536, 606 32- 52, 701/300, 607 1- 76
• US Class Current: 600/554
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/296 for electromyography [EMG]
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/4893 Nerves
• CPC Class Codes: A61B 90/04 Protection of tissue around surgical sites against effects of non-mechanical surgery, e.g. laser surgery protection of eyes against laser radiation A61F9/022

Abstract

System (20) and related methods for performing surgical procedures and assessments, including the use of neurophysiology-based monitoring to determine nerve proximity and nerve direction to surgical instruments (30) employed in accessing a surgical target site.

Claims

1. A method of finding a direction of a nerve from a surgical instrument, the method comprises:

electrically stimulating a first stimulation electrode on a distal region of a surgical instrument configured to advance through tissue to create a distraction corridor with a first set of at least one stimulation current signal until a first initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a first threshold stimulation current level must lie is determined;

electrically stimulating a second stimulation electrode spaced apart from said first electrode with a second set of at least one stimulation current signal until a second initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a second threshold stimulation current level must lie is determined;

processing with a control unit communicatively linked to said first and second electrodes the determined first initial bracket and the determined second initial bracket, said processing including determining the first threshold stimulation current level by narrowing the first initial bracket to a first final bracket and determining the second threshold stimulation current level by narrowing the second initial bracket to a second final bracket;

prior to completing the steps of determining the first and second threshold stimulation current levels, displaying on a display communicatively linked to said control unit, an initial indicator, based on said processing, indicating a general direction of the nerve from the surgical instrument; and

upon completing the steps of determining the first and second threshold stimulation current levels, displaying on the display a subsequent indicator, based on said processing, indicating a more specific direction of the nerve from the surgical instrument.

2. The method of claim 1, wherein said indicator indicating the general direction of a nerve from the surgical instrument comprises displaying an arc indicating the general direction of the nerve from the surgical instrument.

3. The method of claim 2, further comprising displaying the arc indicating the general direction of the nerve from the surgical instrument and narrowing the arc as the control unit successively narrows the first and second initial brackets containing the first and second threshold stimulation current levels.

4. The method of claim 1, further comprising electrically stimulating the first and second stimulation electrodes to bisect each of the first initial bracket and the second initial bracket until the first threshold stimulation current level has been found for the first stimulation electrode and the second threshold stimulation current level has been found for the second stimulation electrode within a predetermined range of accuracy.

5. The method of claim 4, further comprising displaying the arc indicating the general direction of the nerve from the surgical instrument and narrowing the arc as the first and second initial brackets are bisected.

6. The method of claim 1, wherein at least one of the steps of determining the first initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a first threshold stimulation current level must lie and determining the second initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a second threshold stimulation current level must lie further comprises the step of sensing a response of the nerve depolarized by said first set of at least one stimulation signal and said second set of at least one stimulation signal.

7. The method of claim 1, further comprising the additional steps of electrically stimulating a third stimulation electrode spaced apart from said first and second electrodes with a third set of at least one of a third stimulation current signal until a third initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a third threshold stimulation current level must lie is determined;

electrically stimulating a fourth stimulation electrode spaced apart from said first, second, and third electrodes with a fourth set of at least one stimulation current signal until a fourth initial bracket comprising a maximum stimulation current value and a minimum stimulation current value between which a fourth threshold stimulation current level must lie is determined;

processing with a control unit communicatively linked to said third and fourth electrodes the determined third initial bracket and the determined fourth initial bracket, said processing including determining the third threshold stimulation current level by narrowing the third initial bracket to a third final bracket and determining the fourth threshold stimulation current level by narrowing the fourth initial bracket to a fourth final bracket;

prior to completing the steps of determining the third and fourth threshold stimulation current levels, displaying on a display communicatively linked to said control unit, an initial indicator, based on said processing, indicating a general direction of the nerve from the surgical instrument; and

upon completing the steps of determining the third and fourth threshold stimulation current levels, displaying on the display a subsequent indicator, based on said processing, indicating a more specific direction of the nerve from the surgical instrument.

8. The method of claim 7, further comprising displaying the arc indicating the general direction of the nerve from the surgical instrument and narrowing the arc as the control unit successively narrows the first, second, third, and fourth initial brackets containing the first, second, third, and fourth threshold stimulation current levels.

9. The method of claim 7, further comprising electrically stimulating the first, second, third, and fourth stimulation electrodes to bisect each of the first initial bracket, second initial bracket, third initial bracket, and fourth initial bracket until the first threshold stimulation current level has been found for the first stimulation electrode, the second threshold stimulation current level has been found for the second stimulation electrode, the third threshold stimulation current level has been found for the third stimulation electrode, and the fourth threshold stimulation current level has been found for the fourth stimulation electrode within a predetermined range of accuracy.

10. The method of claim 9, further comprising displaying the arc indicating the general direction of the nerve from the surgical instrument and narrowing the arc as the first, second, third, and fourth initial brackets are bisected.

11. The method of claim 7, wherein the maximum stimulation current value of each of the first, second, third, and fourth initial brackets is a current intensity of a stimulation signal that first evokes a neuromuscular response of a predetermined magnitude from a muscle innervated by said nerve and the minimum stimulation current value of the first, second, third, and fourth initial brackets is a current intensity of a stimulation signal that first fails to evoke a neuromuscular response of said predetermined magnitude from said muscle.

12. The method of claim 11, wherein each of the first, second, third, and fourth initial brackets are bisected by stimulating with a current intensity at the midpoint of the bracket.

13. The method of claim 12, wherein the bisection of each bracket is repeated until the width of each bracket is reduced to a predetermined accuracy.

14. The method of claim 13, wherein the stimulation current levels for each of the first, second, third, and fourth electrodes are determined as a value within the respective first, second, third, and fourth brackets after the brackets are reduced to the predetermined accuracy.

15. The method of claim 14, further comprising the step of deriving x and y Cartesian coordinates of the general direction of the nerve with respect to said surgical instrument by using x=i_w²−

i_e² and y=i_s²−

i_n², where i_e, i_w, i_n, and i_s represent the threshold stimulation current levels for the first, second, third, and fourth electrodes.

16. The method of claim 14, further comprising the step of determining a three-dimensional vector from a reference point on the surgical instrument to a nerve.

17. The method of claim 16, further comprising the step of determining a three-dimensional vector from a reference point on the surgical instrument to a nerve by using:

18. The method of claim 16, further comprising the step of determining a three-dimensional vector from a reference point on the surgical instrument to a nerve by using:

19. The method of claim 16, further comprising the step of displaying the three-dimensional vector to a user.

20. The method of claim 14, further comprising the step of processing the stimulation current thresholds by using

21. The method of claim 14, further comprising the step of processing the stimulation current thresholds by using

22. The method of claim 1, wherein the first set of at least one stimulation signal comprises stimulation signals of sequentially doubled current intensity.

23. The method of claim 22, wherein the second set of at least one stimulation signal comprises stimulation signals of sequentially doubled current intensity.

24. The method of claim 23, wherein the maximum stimulation current value of the second initial bracket is a current intensity of a stimulation signal that first evokes a neuromuscular response of a predetermined magnitude from a muscle innervated by said nerve and the minimum stimulation current value of the second initial bracket is a current intensity of a stimulation signal that failed to evoke a neuromuscular response of said predetermined magnitude from said muscle.

25. The method of claim 22, wherein the maximum stimulation current value of the first initial bracket is a current intensity of a stimulation signal that first evokes a neuromuscular response of a predetermined magnitude from a muscle innervated by said nerve and the minimum stimulation current value of the first initial bracket is a current intensity of a stimulation signal that failed to evoke a neuromuscular response of said predetermined magnitude from said muscle.