System for Determining Nerve Direction to a Surgical Instrument

Abstract

A system for performing surgical procedures and assessments. The system includes the use of neurophysiology-based monitoring to determine nerve proximity and nerve direction to surgical instruments employed in accessing a surgical target site.

1 . A method comprising:
 providing one or more electrical stimulation signals with a first stimulation electrode until a first initial bracket within which a first threshold stimulation current level lies is determined based on detecting a response of a nerve depolarized by the one or more electrical stimulation signals provided by the first simulation electrode;   providing one or more electrical stimulation signals with a second stimulation electrode until a second initial bracket within which a second threshold stimulation current level lies is determined based on detecting a response of a nerve depolarized by the one or more electrical stimulation signals provided by the second stimulation electrode;   narrowing the first initial bracket to a first final bracket in which the first threshold stimulation current level lies;   narrowing the second initial bracket to a second final bracket in which the second threshold stimulation current level lies;   determine an arc indicating general direction of a nerve relative to a surgical instrument using the first initial bracket, the second initial bracket, wherein determining a length of the arc is based on:
 the first threshold stimulation current level; and 
 the second threshold stimulation current level; and 
   indicating a general direction of a nerve relative to a surgical instrument by displaying the arc.   
     
     
         2 . The method of  claim 1 , further comprising:
 advancing the surgical instrument through tissue to create an operative corridor to a spinal surgical target site via a lateral, trans-psoas approach.   
     
     
         3 . The method of  claim 1 , further comprising:
 displaying an electromyographic (EMG) response of a muscle.   
     
     
         4 . The method of  claim 1 , further comprising:
 providing one or more electrical stimulation signals with a third stimulation electrode;   providing one or more electrical stimulation signals with a fourth stimulation electrode.   
     
     
         5 . The method of  claim 4 ,
 wherein the first, second, third, and fourth stimulation electrodes are positioned orthogonally to form a cross.   
     
     
         6 . The method of  claim 4 ,
 deriving x and y Cartesian coordinates of the general direction of the nerve.   
     
     
         7 . The method of  claim 6 , further comprising:
 deriving the x Cartesian coordinate based on a difference between a threshold stimulation current associated with the first stimulation electrode and the second stimulation electrode; and   deriving the y Cartesian coordinate based on a difference between a threshold stimulation current associated with the third stimulation electrode and the fourth stimulation electrodes.   
     
     
         8 . The method of  claim 6 , further comprising:
 deriving the x Cartesian coordinate based on a difference between squared threshold stimulation current associated with the first and second electrodes; and   deriving the x Cartesian coordinate based on a difference between squared threshold stimulation current associated with the third and fourth electrodes.   
     
     
         9 . The method of  claim 4 , further comprising:
 determining a three-dimensional vector from a reference point to the nerve; and   displaying a representation of the three-dimensional vector.   
     
     
         10 . The method of  claim 9 , further comprising:
 determining the three-dimensional vector using:   
       
         
           
             
               
                 x 
                 = 
                 
                   
                     1 
                     
                       4 
                       ⁢ 
                       R 
                       ⁢ 
                       K 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         i 
                         w 
                       
                       - 
                       
                         i 
                         e 
                       
                     
                     ) 
                   
                 
               
               , 
               
                 
 
               
               ⁢ 
               
                 y 
                 = 
                 
                   
                     1 
                     
                       4 
                       ⁢ 
                       R 
                       ⁢ 
                       K 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         i 
                         s 
                       
                       - 
                       
                         i 
                         n 
                       
                     
                     ) 
                   
                 
               
               , 
               
                 
 
               
               ⁢ 
               and 
             
           
         
         
           
             
               
                 z 
                 = 
                 
                   
                     1 
                     
                       4 
                       ⁢ 
                       R 
                       ⁢ 
                       K 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         i 
                         c 
                       
                       - 
                       
                         i 
                         k 
                       
                     
                     ) 
                   
                 
               
               , 
             
           
         
         where K is a proportionality constant denoting a relationship between current and distance; 
         where R is a cannula radius; 
         where i e , i w , i n , and i s , represent threshold stimulation current levels for the first stimulation electrode, the second stimulation electrode, the third stimulation electrode, and the fourth stimulation electrode, respectively; 
         where i k  is a stimulation current threshold of an electrode; and 
         where i c  is calculated from:
     i   c =1/4( i   w   +i   e   +i   s   +i   n )− KR   2 .
 
 
       
     
     
         11 . A method comprising:
 providing a first surgical accessory having at least a first stimulation electrode on a distal region and a second stimulation electrode at a second region;   providing at least one sensor configured to detect an evoked response from nerve tissue depolarized by electrical stimulation;   electrically stimulating the first stimulation electrode with a first set of at least one electrical stimulation signal until a first initial bracket within which a first threshold stimulation current level must lie is determined;   electrically stimulating the second stimulation electrode with a second set of at least one electrical stimulation signal until a second initial bracket within which a second threshold stimulation current level must lie is determined;   processing the determined first and second initial brackets to find the direction of a nerve from the surgical accessory, 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; 
   displaying an arc indicating a general direction of the nerve from the surgical accessory, the general direction based on the determinations of the first initial bracket and the second initial bracket; and   narrowing a length of the arc based on the determinations of the first threshold stimulation current level and the second threshold stimulation current level, the length of the arc being at least partially indicative of the direction of the nerve from the surgical accessory.   
     
     
         12 . The method of  claim 11 , further comprising:
 advancing the first surgical accessory through tissue to create an operative corridor to a surgical target site of a spine via a lateral, trans-psoas approach.   
     
     
         13 . The method of  claim 11 ,
 slidably placing a K-wire within the surgical accessory.   
     
     
         14 . The method of  claim 11 , further comprising:
 actuating a button of a handle coupled to the first surgical accessory,   wherein the one or more electrical stimulation signals are provided responsive to the actuating.   
     
     
         15 . The method of  claim 11 , further comprising:
 electrically stimulating the first stimulation electrode with a first electrical stimulation signal of the first set of at least one electrical stimulation signal;   determining whether the first threshold stimulation current level has been bracketed,   stimulating the second stimulation electrode with a second electrical stimulation signal of the first set of at least one electrical stimulation signal and determine whether the second threshold stimulation current level has been bracketed.   
     
     
         16 . The method of  claim 11 , wherein the first and second electrical stimulation signals are equal. 
     
     
         17 . The method of  claim 11 , further comprising:
 electrically stimulating the first and second stimulation electrodes to bisect each of the first and second initial brackets 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.   
     
     
         18 . The method of  claim 11 , further comprising:
 emitting a sound responsive to a distance between the first surgical accessory and the nerve reaching a predetermined level.   
     
     
         19 . The method of  claim 11 , further comprising:
 determining the first initial bracket and second initial bracket by detecting a response of the nerve depolarized by the first set of at least one electrical stimulation signal and a second set of at least one electrical stimulation signal.   
     
     
         20 . The method of  claim 11 , further comprising:
 electrically stimulating a third stimulation electrode with a third set of at least one stimulation signal until a third initial bracket within which a third threshold stimulation current level must lie is determined;   electrically stimulating a fourth stimulation electrode until a fourth initial bracket within which a fourth threshold stimulation current level must lie is determined;   processing the determined third and fourth initial brackets to find the direction of the nerve, 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; 
   displaying a second arc indicating the direction of the nerve, the direction based on the determinations of said third initial bracket and said fourth initial bracket; and   narrowing a length of the displayed second arc based on the determinations of said third threshold stimulation current level and said fourth threshold stimulation current level.