Neurologic monitoring system and method

Abstract

A method, system, and products that allow for accurate localization, virtual depiction, and testing of nerve(s) or neural structures that course through or around a proposed surgical site are described. The method and system employs a variety of types of neurodiagnostic tests that incorporate sensory, motor, and mixed nerve conduction studies in an orthodromic and antidromic fashion as well as utilizing triggered electromyography. This method, system, and products allow for a much more specific and sensitive method to assess the baseline function and continued integrity of nerves and neural structures prior to, during, and after a surgical procedure.

1 . A method for monitoring neural function of a target nerve with the use of a neuromonitoring machine, the method comprising:
 providing a stimulus to a proximal nerve and obtaining a response at a distal nerve;   providing a stimulus to a distal nerve and obtaining a response at a proximal nerve, wherein the distal nerve is distal to the target nerve and the proximal nerve is proximal to the target nerve; and   comparing the distal nerve response or the proximal nerve response to a baseline response.   
     
     
         2 . The method of  claim 1 , further comprising placing a proximal electrode at or in proximity to the proximal nerve and placing a distal electrode at or in proximity to the distal nerve. 
     
     
         3 . The method of  claim 2 , further comprising receiving a response with the proximal electrode and providing a stimulus with the proximal electrode. 
     
     
         4 . The method of  claim 2 , further comprising receiving a response with the distal electrode and providing a stimulus with the distal electrode. 
     
     
         5 . The method of  claim 1 , wherein the baseline response is a measurement of the target nerve function when the target nerve is not under compression or traction. 
     
     
         6 . The method of  claim 1 , wherein the proximal nerve is a L1, L2, or L3 nerve root. 
     
     
         7 . The method of  claim 1 , wherein the distal nerve is a nerve corresponding to a dermatome, a myotome, or a femoral nerve. 
     
     
         8 . The method of  claim 1 , further comprising obtaining one or more of nerve conduction velocity, elapsed time between stimulus and response, nerve latency time, or response amplitude. 
     
     
         9 . The method of  claim 1 , further comprising diminishing traction or compressive forces on the target nerve when the distal nerve response or the proximal nerve response is not substantially the same to the baseline response. 
     
     
         10 . The method of  claim 1 , further comprising testing sensory nerves orthodromically and antidromically. 
     
     
         11 . The method of  claim 1 , further comprising testing sensory nerves, motor nerves, or mixed neural structures having sensory and motor nerves. 
     
     
         12 . The method of  claim 1 , further comprising conducting electromyography. 
     
     
         13 . A system for monitoring neural function of a nerve, comprising:
 a first electrode configured to be suitable for nerve stimulus delivery and nerve response recordation;   a first slave box connected to the first electrode, the slave box further comprising electrical stimulus circuitry and amplification circuitry to either deliver a stimulus to the first electrode via the stimulus circuitry or to receive a response from the first electrode via the amplification circuitry; and   a first switch having a first position to connect the first electrode to the electrical stimulus circuitry and disconnect the first electrode from the amplification circuitry to allow delivery of a nerve stimulus at the first electrode, and a second position to connect the first electrode to the amplification circuitry and disconnect the first electrode from the electrical stimulus circuitry to allow recording a nerve response at the first electrode.   
     
     
         14 . The system of  claim 13 , wherein the switch is a hard wired switch or a software switch. 
     
     
         15 . The system of  claim 13 , further comprising a neuromonitoring machine that controls the connection of the first electrode to the stimulus circuitry and to the amplification circuitry. 
     
     
         16 . The system of  claim 13 , comprising a hard switch that controls the connection of the first electrode to the stimulus circuitry and the amplification circuitry. 
     
     
         17 . The system of  claim 13 , further comprising a ground electrode connected to the amplification circuitry. 
     
     
         18 . The system of  claim 13 , wherein in the first switch position the first electrode is connected to an anode in the stimulus circuitry, and the switch in the second position connects the first electrode to an active contact in the amplification circuitry. 
     
     
         19 . The system of  claim 13 , wherein the amplification circuitry comprises differential amplification circuitry. 
     
     
         20 . The system of  claim 13 , wherein the system further comprises a neuromonitoring machine configured to automatically connect the first electrode to the electrical stimulus circuitry, and automatically connect the first electrode to the amplification circuitry. 
     
     
         21 . The system of  claim 20 , further comprising a second electrode configured to be suitable for nerve stimulus delivery and nerve response recordation;
 a second slave box connected to the second electrode, the second slave box further comprising second electrical stimulus circuitry and second amplification circuitry to either deliver a stimulus to the second electrode via the second stimulus circuitry or to receive a response from the second electrode via the second amplification circuitry;   and a second switch having a first position to connect the second electrode to the second electrical stimulus circuitry and disconnect the second electrode from the second amplification circuitry to allow delivery of a nerve stimulus at the second electrode, and a second position to connect the second electrode to the second amplification circuitry and disconnect the second electrode from the second electrical stimulus circuitry to allow recording a nerve response at the second electrode, and the neuromonitoring machine is configured to automatically connect the second electrode to the amplification circuitry of the second slave box when the first electrode is connected to the electrical stimulus circuitry of the first slave box, and to automatically connect the second electrode to the electrical stimulus circuitry of the second slave box when the first electrode is connected to the amplification circuitry of the first slave box.   
     
     
         22 . The system of  claim 13 , further comprising an electrode with a plurality of independent contacts at a distal tip of the electrode, wherein the electrode is electrically coupled to the slave box, and each of the contacts is provided at a different location of the electrode. 
     
     
         23 . The system of  claim 21 , further comprising a third electrode connected to the first slave box and a fourth electrode connected to the second slave box, wherein the first switch is in the first position and connects the first and third electrodes to the electrical stimulus circuitry of the first slave box, and the second switch is in the second position and connects the second and fourth electrodes to the amplification circuitry of the second slave box. 
     
     
         24 . The system of  claim 21 , further comprising a third electrode connected to the first slave box and a fourth electrode connected to the second slave box, wherein the first switch is in the second position and connects the first and third electrodes to the amplification circuitry of the first slave box, and the second switch is in the first position and connects the second and fourth electrodes to the electrical stimulus circuitry of the second slave box. 
     
     
         25 . The system of  claim 13 , further comprising a second electrode connected to the slave box, wherein the switch being in the first position connects the second electrode to the electrical stimulus circuitry and disconnects the second electrode from the amplification circuitry, and the switch being in the second position connects the second electrode to the amplification circuitry and disconnects the second electrode from the electrical stimulus circuitry. 
     
     
         26 . The system of  claim 25 , wherein the electrical stimulus circuitry comprises a cathode and anode, and the switch being in the first position connects the first electrode to the cathode and the second electrode to the anode. 
     
     
         27 . The system of  claim 25 , wherein the amplification circuitry includes a reference contact and an active contact, and the switch being in the second position connects the first electrode to the reference contact and the second electrode to the active contact. 
     
     
         28 . The system of  claim 13 , further comprising a second electrode configured to be suitable for nerve stimulus delivery and nerve response recordation;
 a second slave box connected to the second electrode, the second slave box further comprising second electrical stimulus circuitry and second amplification circuitry to either deliver a stimulus to the second electrode via the second stimulus circuitry or to receive a response from the second electrode via the second amplification circuitry;   and a second switch having a first position to connect the second electrode to the second electrical stimulus circuitry and disconnect the second electrode from the second amplification circuitry to allow delivery of a nerve stimulus at the second electrode, and a second position to connect the second electrode to the second amplification circuitry and disconnect the second electrode from the second electrical stimulus circuitry to allow recording a nerve response at the second electrode.   
     
     
         29 . The system of  claim 28 , further comprising a third electrode connected to the first slave box and a fourth electrode connected to the second slave box, wherein the first switch is in the first position and connects the first and third electrodes to the electrical stimulus circuitry of the first slave box, and the second switch is in the second position and connects the second and fourth electrodes to the amplification circuitry of the second slave box. 
     
     
         30 . The system of  claim 28 , further comprising a third electrode connected to the first slave box and a fourth electrode connected to the second slave box, wherein the first switch is in the second position and connects the first and third electrodes to the amplification circuitry of the first slave box, and the second switch is in the first position and connects the second and fourth electrodes to the electrical stimulus circuitry of the second slave box. 
     
     
         31 . A localization probe for detecting the location of a nerve, comprising:
 a shaft having a distal end and a proximal end; and   an active tip on the distal end, wherein the active tip has an exposed portion of an electroconductive material surrounded by insulation, and the active tip is configured to rotate.   
     
     
         32 . The probe of  claim 31 , wherein the active tip defines a circumference having a portion of the circumference formed from the electroconductive material and the remainder of the circumference is formed from insulation. 
     
     
         33 . The probe of  claim 31 , wherein the electroconductive material extends the length of the probe and is connected to a stimulus circuit. 
     
     
         34 . A method for monitoring a nerve with the use of a neuromonitoring machine, comprising:
 obtaining a baseline response of a neural structure by stimulating a nerve at a proximal location and receiving a response at a distal location and stimulating a nerve at a distal location and receiving a response at a proximal location, the baseline response being defined as a response when the neural structure is not experiencing surgical trauma;   locating the neural structure by providing stimulation in a unidirectional manner and receiving a response from a nerve that is proximal to the stimulation location and distal to the stimulation location;   causing compression or tension in proximity to the localized neural structure while stimulating a nerve at a proximal location and receiving a response at a distal location and stimulating a nerve at a distal location and receiving a response at a proximal location; and   comparing the nerve responses obtained when the medical device is in proximity to the localized neural structure with the baseline response.   
     
     
         35 . A neuromonitoring electrode, comprising:
 an electroconductive core material;   an insulator material surrounding the core material;   a blunt distal end having exposed core material; and   a proximal end having exposed core material, wherein the neuromonitoring electrode is flexible.   
     
     
         36 . An arc introducer apparatus, comprising:
 a rotating axis; and   a radius arm connected to the rotating axis, the radius arm configured to connect to an arc introducer needle;   wherein the arc introducer apparatus is configured to be inserted over a guidewire.   
     
     
         37 . The arc introducer apparatus of  claim 36 , further comprising an arc introducer needle on the radius arm on an opposite side to the rotating axis. 
     
     
         38 . The arc introducer apparatus of  claim 37 , wherein the radius arm is rigid and essentially linear and the arc introducer needle is rigid and has a radius of curvature. 
     
     
         39 . A method for placing a neuromonitoring electrode within a tissue of a body, comprising:
 placing a guidewire within a body to reach a deep tissue;   inserting the radius introducer apparatus of  claim 37  over the guidewire to be approximately flush to a surface of the body;   adjusting a radius arm of the radius introducer apparatus to a length approximately equal to the depth of the guidewire inside the body;   pivoting the radius arm with the arc introducer needle to insert the arc introducer needle to reach a neural structure to be monitored; and   inserting a flexible neuromonitoring electrode through the arc introducer needle, and removing the arc introducer needle to place the electrode at or close to the neural structure to be monitored.