System and Methods for Determining Nerve Direction to a Surgical Instrument

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.

1 . A system comprising:
 a surgical accessory having at least one stimulation electrode; and   a control unit capable of electrically stimulating said at least one stimulation electrode on said surgical accessory, sensing a response of a nerve depolarized by said stimulation, determining a direction from the surgical accessory to the nerve based upon the sensed response, and communicating said direction to a user.   
     
     
         2 . The system of  claim 1 , further comprising an electrode configured to sense a neuromuscular response of a muscle coupled to said depolarized nerve, the electrode being operable to send the response to the control unit. 
     
     
         3 . The system of  claim 1 , wherein said surgical accessory comprises a system for establishing an operative corridor to a surgical target site. 
     
     
         4 . The system of  claim 3 , wherein said system for establishing an operative corridor to a surgical target site comprises a series of sequential dilation cannulae, at least one cannula having said at least one stimulation electrode near a distal end. 
     
     
         5 . The system of  claim 4 , wherein said system for establishing an operative corridor to a surgical target site further comprises a K-wire. 
     
     
         6 . The system of  claim 5 , wherein said K-wire has a first stimulation electrode at a distal tip of the K-wire. 
     
     
         7 . The system of  claim 6 , wherein said K-wire has a second stimulation electrode away from the distal tip. 
     
     
         8 . The system of  claim 6 , wherein said K-wire is slidably received in the surgical accessory, the surgical accessory having a plurality of electrodes. 
     
     
         9 . The system of  claim 3 , wherein said system for establishing an operative corridor to a surgical target site is configured to access a spinal target site. 
     
     
         10 . The system of  claim 9 , wherein said system for establishing an operative corridor to a surgical target site is configured to establish said operative corridor via a lateral, trans-psoas approach. 
     
     
         11 . The system of  claim 1 , further comprising a handle coupled to the surgical accessory, the handle having at least one button for initiating the electrical stimulation from said control unit to said at least one stimulation electrode on said surgical accessory. 
     
     
         12 . The system of  claim 1 , wherein the control unit comprises a display operable to display an electromyographic (EMG) response of the muscle. 
     
     
         13 . The system of  claim 1 , wherein the control unit comprises a touch-screen display operable to receive commands from a user. 
     
     
         14 . The system of  claim 1 , wherein the surgical accessory comprises a plurality of stimulation electrodes. 
     
     
         15 . The system of  claim 14 , wherein the stimulation electrodes are positioned near a distal end of the surgical accessory. 
     
     
         16 . The system of  claim 14 , wherein the stimulation electrodes are positioned in a two-dimensional plane. 
     
     
         17 . The system of  claim 14 , wherein the stimulation electrodes are positioned orthogonally to form a cross. 
     
     
         18 . The system of  claim 17 , the control unit derives x and y Cartesian coordinates of a nerve direction with respect to the surgical accessory by using x=i w   2 −i e   2  and y=i s   2   −i   n   2  where i e , i w , i n , and i s  represent stimulation current thresholds for east, west, north, and south electrodes. 
     
     
         19 . The system of  claim 14 , wherein the stimulation electrodes comprise a first set of electrodes in a first two-dimensional plane and a second set of at least one electrode in another plane that is parallel to the first plane. 
     
     
         20 . The system of  claim 19 , wherein the stimulation electrodes form a tetrahedron. 
     
     
         21 . The system of  claim 19 , wherein the control unit is configured to determine a three-dimensional vector from a reference point on the surgical accessory to a nerve. 
     
     
         22 . The system of  claim 21 , wherein the control unit is configured to determine a three-dimensional vector from a reference point on the surgical accessory to a nerve by using: 
       
         
           
             
               x 
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       w 
                       2 
                     
                     - 
                     
                       d 
                       e 
                       2 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             
               y 
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       s 
                       2 
                     
                     - 
                     
                       d 
                       n 
                       2 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             and 
           
         
         
           
             
               z 
               = 
               
                 
                   1 
                   
                     4 
                      
                     D 
                   
                 
                  
                 
                   
                     ( 
                     
                       
                         d 
                         o 
                         2 
                       
                       - 
                       
                         d 
                         k 
                         2 
                       
                     
                     ) 
                   
                   . 
                 
               
             
           
         
       
     
     
         23 . The system of  claim 21 , wherein the control unit is configured to determine a three-dimensional vector from a reference point on the surgical accessory to a nerve by using: 
       
         
           
             
               x 
               = 
               
                 
                   1 
                   
                     4 
                      
                     
                         
                     
                      
                     RK 
                   
                 
                  
                 
                   ( 
                   
                     
                       i 
                       w 
                     
                     - 
                     
                       i 
                       e 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             
               y 
               = 
               
                 
                   1 
                   
                     4 
                      
                     
                         
                     
                      
                     RK 
                   
                 
                  
                 
                   ( 
                   
                     
                       i 
                       s 
                     
                     - 
                     
                       i 
                       n 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             and 
           
         
         
           
             
               z 
               = 
               
                 
                   1 
                   
                     4 
                      
                     DK 
                   
                 
                  
                 
                   ( 
                   
                     
                       i 
                       c 
                     
                     - 
                     
                       i 
                       k 
                     
                   
                   ) 
                 
               
             
           
         
       
       where i x  is a stimulation current threshold of a corresponding stimulation electrode (west, east, south or north), i k  is the stimulation current threshold of a k-wire electrode, i c  is calculated from: 
       
         
           
             
               
                 
                   i 
                   c 
                 
                 + 
                 
                   KR 
                   2 
                 
               
               = 
               
                 
                   1 
                   4 
                 
                  
                 
                   
                     ( 
                     
                       
                         i 
                         w 
                       
                       + 
                       
                         i 
                         e 
                       
                       + 
                       
                         i 
                         s 
                       
                       + 
                       
                         i 
                         n 
                       
                     
                     ) 
                   
                   . 
                 
               
             
           
         
       
     
     
         24 . The system of  claim 21 , wherein the control unit is further configured to display the three-dimensional vector to a user. 
     
     
         25 . The system of  claim 14 , wherein the stimulation electrodes comprise two pairs of electrodes. 
     
     
         26 . The system of  claim 14 , wherein the stimulation electrodes comprise a first electrode at a first longitudinal level of the surgical accessory and a second electrode at a second longitudinal level of the surgical accessory. 
     
     
         27 . The system of  claim 14 , wherein the control unit is configured to electrically stimulate a first stimulation electrode with a first current signal, determine whether a first stimulation current threshold has been bracketed, stimulate a second stimulation electrode with a second current signal, and determine whether a second stimulation current threshold has been bracketed. 
     
     
         28 . The system of  claim 27 , wherein first and second current signals are equal. 
     
     
         29 . The system of  claim 27 , wherein the control unit is further configured to determine a first range for the first stimulation current threshold, and determine a second range for the second stimulation current threshold, each range having a maximum stimulation current threshold value and a minimum stimulation current threshold value. 
     
     
         30 . The system of  claim 29 , wherein the control unit is configured to process the first and second ranges by using x min =i e,min   2 −i e,max   2 ; x max =i w,max   2 −i e,min   2 ; y min =i s,min   2 −i n,max   2 ; y max =i s,max   2 −i n,min   2 , where i e , i w , i n , and i s  represent stimulation current thresholds for east, west, north, and south electrodes. 
     
     
         31 . The system of  claim 29 , wherein the control unit is configured to process the first and second ranges by using 
       
         
           
             
               
                 x 
                 min 
               
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       
                         w 
                         , 
                         min 
                       
                       2 
                     
                     - 
                     
                       d 
                       
                         e 
                         , 
                         max 
                       
                       2 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             
               
                 x 
                 max 
               
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       
                         w 
                         , 
                         max 
                       
                       2 
                     
                     - 
                     
                       d 
                       
                         e 
                         , 
                         min 
                       
                       2 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             
               
                 y 
                 min 
               
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       
                         s 
                         , 
                         min 
                       
                       2 
                     
                     - 
                     
                       d 
                       
                         n 
                         , 
                         max 
                       
                       2 
                     
                   
                   ) 
                 
               
             
           
         
         
           
             
               
                 y 
                 max 
               
               = 
               
                 
                   1 
                   
                     4 
                      
                     R 
                   
                 
                  
                 
                   ( 
                   
                     
                       d 
                       
                         s 
                         , 
                         max 
                       
                       2 
                     
                     - 
                     
                       d 
                       
                         n 
                         , 
                         min 
                       
                       2 
                     
                   
                   ) 
                 
               
             
           
         
       
       where d is a distance from a nerve to east, west, north, and south electrodes. 
     
     
         32 . The system of  claim 29 , wherein the control unit is configured to process the first and second ranges and display an arc indicating a general direction of a nerve from the surgical accessory. 
     
     
         33 . The system of  claim 27 , wherein the control unit is further configured to electrically stimulate the first stimulation electrode with a third current signal, determine whether the first stimulation current threshold has been bracketed, stimulate the second stimulation electrode with a fourth current signal, and determine whether the second stimulation current threshold has been bracketed. 
     
     
         34 . The system of  claim 33 , wherein the control unit is configured to electrically stimulate each electrode until a stimulation current threshold has been bracketed. 
     
     
         35 . The system of  claim 34 , wherein the control unit is configured to display an arc indicating a general direction of a nerve from the surgical accessory and narrow the arc as stimulation current thresholds are bracketed. 
     
     
         36 . The system of  claim 34 , wherein the control unit is further configured to electrically stimulate the first and second stimulation electrodes to bisect each bracket until a first stimulation current threshold has been found for the first stimulation electrode and a second stimulation current threshold has been found for the second stimulation electrode within a predetermined range of accuracy. 
     
     
         37 . The system of  claim 36 , wherein the control unit is configured to display an arc indicating a general direction of a nerve from the surgical accessory and narrow the arc as stimulation current threshold brackets are bisected. 
     
     
         38 . The system of  claim 1 , wherein the control unit is configured to emit a sound when the control unit determines a distance between the surgical accessory and the nerve has reached a predetermined level. 
     
     
         39 . The system of  claim 1 , wherein the control unit is configured to emit a sound that indicates a distance between the surgical accessory and the nerve. 
     
     
         40 . The system of  claim 1 , wherein the surgical accessory is dimensioned to be inserted percutaneously through a hole to a surgical site.