System and methods for determining nerve proximity, direction, and pathology during surgery

Abstract

The present invention involves systems and methods for determining nerve proximity, nerve direction, and pathology relative to a surgical instrument based on an identified relationship between neuromuscular responses and the stimulation signal that caused the neuromuscular responses.

What is claimed is: 
     
         1 . A method comprising:
 delivering a plurality of stimulation signals to a stimulation electrode on a surgical access instrument positioned within tissue of a patient that contains a spinal nerve;   receiving a plurality of voltage response values detected by a plurality of leg muscle sensors coupled to different leg muscles;   determining a value of an unknown threshold nerve stimulation amplitude required to evoke a threshold response from any one of the different leg muscles; and   detecting whether stimulation current thresholds are changing as the surgical access instrument is advanced along a selected path toward a targeted intervertebral disc by incrementing or decrementing simulation current level delivered by the stimulation electrode on the surgical access instrument by an amount.   
     
     
         2 . The method of  claim 1 , wherein the value of the unknown threshold nerve stimulation amplitude is determined using the steps of bracketing the unknown threshold nerve stimulation amplitude by determining a first stimulation amplitude that does not evoke the threshold response from any of the different leg muscles and a second stimulation amplitude that does evoke the threshold response from at least one of the different leg muscles, repeatedly bisecting the bracket that includes the threshold nerve stimulation amplitude until a final bracket of a predetermined width is reached, and selecting the threshold nerve stimulation amplitude from the final bracket. 
     
     
         3 . The method of  claim 1 , further comprising:
 determining which range from a predetermined group of ranges the determined threshold nerve stimulation amplitude is located in; and   communicating on a display an indicator corresponding to the determined range from the predetermined group of ranges as an indicator of nerve proximity to the surgical access instrument.   
     
     
         4 . The method of  claim 1 , wherein whether the stimulation current level is incremented or decremented is determined as a function of evoked responses from one or more of the plurality of leg muscle sensors. 
     
     
         5 . The method of  claim 1 , further comprising:
 detecting whether stimulation current thresholds are changing as the surgical access instrument is advanced along the selected path toward the targeted intervertebral disc by incrementing or decrementing simulation current level delivered by the stimulation electrode on the surgical access instrument by 0.1 mA.   
     
     
         6 . The method of  claim 1 , further comprising:
 entering a monitoring mode in response to determining the value of the unknown threshold nerve stimulation amplitude, wherein the monitoring mode is continued while the threshold nerve stimulation amplitude remains in the final bracket.   
     
     
         7 . The method of  claim 6 , wherein the threshold nerve stimulation amplitude is determined to be outside the final bracket when the threshold nerve stimulation amplitude fails to fall within upper and lower ends of the final bracket three times. 
     
     
         8 . The method of  claim 3 , wherein the indicator corresponding to the determined range from the predetermined group of ranges includes a color display. 
     
     
         9 . The method of  claim 8 , wherein the predetermined group of ranges includes three predetermined ranges and the color displayed is one of three different colors, each of the three different colors corresponding to one of the three predetermined ranges. 
     
     
         10 . The method of  claim 9 , wherein the color is one of red, yellow, and green depending on the applicable range. 
     
     
         11 . The method of  claim 1 , further comprising:
 causing the display to display at least one of a name and a symbol representative of the surgical access instrument being used.   
     
     
         12 . The method of  claim 1 , wherein the threshold response is a voltage response of a predetermined peak-to-peak voltage. 
     
     
         13 . The method of  claim 12 , wherein the predetermined peak-to-peak voltage is approximately 100 μV. 
     
     
         14 . The method of  claim 1 , wherein the threshold response is a peak-to-peak voltage with peaks at a time T 1  and a time T 2  relative to a stimulation delivery time. 
     
     
         15 . The method of  claim 1 , wherein the surgical access instrument is a dilator cannula. 
     
     
         16 . A method comprising:
 delivering a plurality of stimulation signals to a stimulation electrode on a surgical access instrument positioned within tissue of a patient that contains a spinal nerve;   receiving a plurality of voltage response values detected by a plurality of leg muscle sensors coupled to different leg muscles;   determining a value of an unknown threshold nerve stimulation amplitude required to evoke a threshold response from any one of the different leg muscles;   entering a monitoring mode in response to determining the value of the unknown threshold nerve stimulation amplitude; and   detecting whether stimulation current thresholds are changing as the surgical access instrument is advanced along a selected path toward a targeted intervertebral disc by incrementing or decrementing simulation current level delivered by the stimulation electrode on the surgical access instrument by an amount.   
     
     
         17 . The method of  claim 16 , wherein the value of the unknown threshold nerve stimulation amplitude is determined using the steps of bracketing the unknown threshold nerve stimulation amplitude by determining a first stimulation amplitude that does not evoke the threshold response from any of the different leg muscles and a second stimulation amplitude that does evoke the threshold response from at least one of the different leg muscles, repeatedly bisecting the bracket that includes the threshold nerve stimulation amplitude until a final bracket of a predetermined width is reached, and selecting the threshold nerve stimulation amplitude from the final bracket. 
     
     
         18 . The method of  claim 16 , further comprising:
 determining which range from a predetermined group of ranges the determined threshold nerve stimulation amplitude is located in; and   communicating on a display an indicator corresponding to the determined range from the predetermined group of ranges as an indicator of nerve proximity to the surgical access instrument.   
     
     
         19 . The method of  claim 16 , wherein whether the stimulation current level is incremented or decremented is determined as a function of evoked responses from one or more of the plurality of leg muscle sensors. 
     
     
         20 . The method of  claim 16 , further comprising:
 detecting whether stimulation current thresholds are changing as the surgical access instrument is advanced along the selected path toward the targeted intervertebral disc by incrementing or decrementing simulation current level delivered by the stimulation electrode on the surgical access instrument by 0.1 mA.