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

• US 20050182454A1
• Filed: 01/09/2004
• Published: 08/18/2005
• Est. Priority Date: 07/11/2001
• Status: Active Grant

• Current Assignee: Nuvasive Incorporated
• Original Assignee: Nuvasive Incorporated
• Inventors: Blewett, Jeffrey, Kaula, Norbert F., Gharib, James, Medeiros, Goretti
• Granted Patent: US 8,068,912 B2
• Time in Patent Office: Days
• US Class Current: 607/48
• CPC Class Codes: A61B 17/00 Surgical instruments, devices or methods, e.g. tourniquets A61B18/00 takes precedence; contraceptive devices, pessaries, or applicators therefor A61F6/00; eye surgery A61F9/007; ear surgery A61F11/00
• CPC Class Codes: A61B 17/02 for holding wounds open; Tractors specula A61B1/32 ; drainage appliances for wounds A61M27/00
• CPC Class Codes: A61B 18/00 Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body eye surgery A61F9/007; ear surgery A61F11/00
• CPC Class Codes: A61B 2017/00039 Electric or electromagnetic phenomena other than conductivity, e.g. capacity, inductivity, Hall effect
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/4893 Nerves
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• CPC Class Codes: A61B 5/743 Displaying an image simultaneously with additional graphical information, e.g. symbols, charts, function plots
• CPC Class Codes: A61N 1/08 Arrangements or circuits for monitoring, protecting, controlling or indicating for external stimulators A61N1/3603; for implantable neurostimulators A61N1/36128; for heart stimulators A61N1/37; for defibrillators A61N1/3925
• CPC Class Codes: A61N 1/36 for stimulation
• CPC Class Codes: A61N 1/36017 with leads or electrodes penetrating the skin

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.

Claims

1. A surgical system, comprising:

a control unit having at least one of computer programming software, firmware and hardware capable of delivering a stimulation signal, receiving and processing neuromuscular responses due to the stimulation signal, and identifying a relationship between the neuromuscular response and the stimulation signal; and

a surgical instrument having at least one stimulation electrode electrically coupled to said control unit for transmitting the stimulation signal, wherein said control unit is capable of determining at least one of nerve proximity, nerve direction, and nerve pathology relative to the surgical instrument based on the identified relationship between the neuromuscular response and the stimulation signal.

2. The surgical system of claim 1 and further, wherein said control unit is further equipped to communicate at least one of alpha-numeric and graphical information to a user regarding at least one of nerve proximity, nerve direction, and nerve pathology.

3. The surgical system of claim 1 and further, wherein the surgical instrument may comprise at least one of a device for maintaining contact with a nerve during surgery, a device for accessing a surgical target site, and a device for testing screw placement integrity.

4. The surgical system of claim 1 and further, wherein the surgical instrument comprises a nerve root retractor and wherein the control unit determines nerve pathology based on the identified relationship between the neuromuscular response and the stimulation signal.

5. The surgical system of claim 1 and further, wherein the surgical instrument comprises a dilating instrument and wherein the control unit determines at least one of proximity and direction between a nerve and the instrument based on the identified relationship between the neuromuscular response and the stimulation signal.

6. The surgical system of claim 5 and further, wherein the dilating instrument comprises at least one of a K-wire, an obturator, a dilating cannula, and a working cannula.

7. The surgical system of claim 1 and further, wherein the surgical instrument comprises a screw test probe and wherein the control unit determines the proximity between the screw test probe and an exiting spinal nerve root to assess whether a medial wall of a pedicle has been breached by at least one of hole formation and screw placement.

8. A system comprising:

an instrument with an electrode configured to transmit electrical current signals with adjustable amplitudes to a tissue;

a sensor configured to detect a voltage response from a muscle; and

a control unit coupled to the instrument and the sensor, the control unit being configured to (a) command the electrode to transmit electrical current signals with adjustable amplitudes, (b) receive a voltage response from the sensor, and (c) determine a threshold stimulation current for a predetermined threshold voltage response value, the threshold stimulation current corresponding to a distance between the electrode and a nerve associated with the muscle.

9. The system of claim 8, wherein the control unit is configured to determine a peak-to-peak amplitude of the voltage response and derive a threshold response voltage vs. stimulation current recruitment curve to determine a proximity of a nerve to the electrode.

10. The system of claim 8, wherein the control unit comprises a display configured to display the determined threshold stimulation current.

11. The system of claim 8, wherein the control unit comprises a display configured to display a response voltage vs. stimulation current recruitment curve.

12. The system of claim 8, wherein the control unit comprises a display configured to display an advance icon to a user when the determined threshold stimulation current is above a predetermined level.

13. The system of claim 8, wherein the control unit comprises a display configured to display a hold icon to a user when the determined threshold stimulation current is below a predetermined level.

14. The system of claim 8, wherein the control unit is configured to send a signal to the electrode to generate monophase current pulses with a predetermined duration.

15. The system of claim 8, wherein the control unit is configured to cause the electrode to generate monophase current pulses with a configurable duration.

16. The system of claim 8, wherein the control unit comprises an audio output configured to emit an audible sound to a user, the sound indicating a distance between the electrode and a nerve associated with the muscle.

17. The system of claim 8, wherein the sensor comprises a plurality of electrodes configured to sense electromyographic (EMG) voltage responses from a plurality of muscle groups.

18. The system of claim 8, wherein the instrument comprises a plurality of cannulae with different diameters, each cannula having at least one electrode.

19. The system of claim 8, wherein the instrument comprises a reusable component configured to be inserted through a cannula to a surgical site within a body.

20. The system of claim 8, wherein the instrument comprises a disposable portion.

21. The system of claim 8, wherein the instrument comprises a pedicle screw hole probe.

22. A system comprising:

an instrument with a plurality of electrodes, each electrode being configured to transmit electrical current signals with adjustable amplitudes to a tissue;

a sensor configured to detect voltage responses from a muscle; and

a control unit coupled to the instrument and the sensor, the control unit being configured to (a) control the electrodes to transmit electrical current signals with adjustable amplitudes, (b) receive voltage responses from the sensor, and (c) for each electrode, determine a threshold stimulation current for a predetermined threshold voltage response value, the threshold stimulation currents of the electrodes corresponding to a direction with respect to the electrodes to a nerve associated with the muscle.

23. The system of claim 22, wherein the electrodes comprises four electrodes spaced orthogonally in a two-dimensional plane.

24. The system of claim 22, wherein the control unit is configured to determine a two-dimensional vector from a reference point of the instrument to a nerve by using:

$x=\frac{1}{-4<br><br>R}<br><br>\left(d_1^2-d_3^2\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>y=\frac{1}{-4<br><br>R}<br><br>\left(d_2^2-d_4^2\right).$

25. The system of claim 22, wherein the sensor comprises a plurality of electrodes configured to sense electromyographic (EMG) voltage responses from a plurality of muscle groups.

26. The system of claim 22, wherein the control unit is configured to display the direction of the nerve in the tissue associated with the muscle with respect to the electrodes.

27. An instrument configured to be partially inserted through tissue, the instrument having a plurality of electrodes near a distal end of the instrument, each electrode being configured to generate an electrical current to the tissue, wherein the electrical current stimulates a nerve in the tissue if the instrument is sufficiently close to the nerve.

28. The instrument of claim 27, wherein the instrument comprises a shaft and four electrodes in a two-dimensional plane.

29. The instrument of claim 28, wherein the four electrodes are orthogonal.

30. A system comprising:

an instrument with an electrode configured to transmit electrical current signals with adjustable amplitudes to a nerve;

a sensor configured to detect voltage responses from a muscle associated with the nerve; and

a control unit coupled to the instrument and the sensor, the control unit being configured to (a) control the electrode to transmit electrical current signals with adjustable amplitudes, (b) receive voltage responses from the sensor, and (c) determine a pathology of the nerve associated with the muscle by determining a relationship between a stimulation current and a voltage response.

31. The system of claim 30, wherein the relationship includes at least one of a threshold voltage response and threshold stimulation current.

32. The system of claim 30, wherein the relationship includes a ratio of the stimulation current and the corresponding voltage response.

33. The system of claim 30, wherein the relationship includes at least one of a saturation voltage response and a saturation stimulation current.

34. The system of claim 30, wherein the sensor comprises a plurality of electrodes configured to sense electromyographic (EMG) voltage responses from a plurality of muscle groups.

35. The system of claim 30, wherein the control unit comprises an audio output configured to emit an audible sound indicating a voltage response.

36. The system of claim 30, wherein the instrument comprises a nerve root retractor with a curved distal region.

37. A computer configured to (a) receive a plurality of voltage response signals, each voltage response value corresponding in time to a stimulation current signal with a configurable amplitude, and (b) determine a nerve stimulation current for a pre-determined voltage response value.

38. The computer of claim 37, being further configured to command an instrument to transmit the stimulation current signals.

39. The computer of claim 37, being configured to determine a peak-to-peak amplitude for each voltage response signal.

40. The computer of claim 37, being configured to store a first time duration from a stimulation current signal to a first peak of a voltage response.

41. The computer of claim 40, being configured to store a second time duration from the stimulation current signal to a second peak of the voltage response.

42. The computer of claim 41, being configured to store a plurality of first and second time durations as a plurality of stimulation current signals are generated and a plurality of voltage response values are received, the processing unit using the plurality of first and second time durations to perform artifact rejection.

43. The computer of claim 37, being configured to execute a bracketing process with a plurality of pre-determined stimulation current levels to determine the stimulation current for the pre-determined voltage response value.

44. The computer of claim 37, being configured to execute a bisecting process with a plurality of pre-determined stimulation current levels to determine the stimulation current for the pre-determined voltage response value.

45. The computer of claim 37, being further configured to communicate the determined stimulation current for the predetermined threshold voltage response value to a user.

46. The computer of claim 37, being further configured to control a display unit configured to display the stimulation current for the pre-determined voltage response value.

47. The computer of claim 37, being further configured to receive user commands.

48. The computer of claim 37, further comprising a touch screen display configured to receive instructions from a user.

49. The computer of claim 37, being configured to receive a plurality of voltage response signals from a plurality of sensors located at various locations of a body.

50. The computer of claim 49, being configured to execute a time-multiplexing process to determine the stimulation current of each sensor for the pre-determined voltage response value.

51. A software application stored in a medium and executable by processor, the software application being configured to (a) receive a plurality of voltage response values and (b) bracket a threshold nerve stimulation current value corresponding to a predetermined threshold voltage response value.

52. The software application of claim 51, being configured to bisect a bracket that includes the threshold nerve stimulation current value corresponding to the predetermined threshold voltage response value.

53. The software application of claim 51, being configured to receive user commands.

54. The software application of claim 51, being configured to activate a nerve proximity determination mode.

55. The software application of claim 51, being configured to activate a nerve direction determination mode.

56. The software application of claim 51, being configured to activate a nerve pathology determination mode.

57. The software application of claim 51, comprising a graphical user interface configured to display a bracketed threshold nerve stimulation current value.

58. The software application of claim 51, comprising a graphical user interface configured to display a name of an instrument being used to deliver a plurality of electrical current signals.

59. The software application of claim 51, comprising a graphical user interface configured to display a symbol of an instrument being used to deliver a plurality of electrical current signals.

60. The software application of claim 51, comprising a graphical user interface configured to display locations of nerves and muscles.

61. The software application of claim 51, comprising a graphical user interface configured to display locations of a plurality of sensors.

62. The software application of claim 51, comprising a graphical user interface configured to display a color that indicates a determined threshold stimulation current value.

63. The software application of claim 51, configured to determine a maximum frequency of stimulation current pulses.

64. A software application stored in a medium and executable by processor, the software application being configured to adjust a frequency and an amplitude of a stimulation electrical current generated by an electrode on an instrument, the electrical current stimulating a nerve when the instrument is placed within a range of the nerve.

65. A module comprising:

an output connector configured to output a signal to an instrument to generate a stimulation electrical current to a tissue;

a plurality of input connectors configured to receive a plurality of voltage signals from a plurality of sensors in response to the stimulation current;

signal conditioning circuitry configured to convert the voltage signals to digital signals; and

a second output connector configured to output digital signals to a control unit.

66. The module of claim 65, further comprising a stimulator drive and steering circuitry.

67. The module of claim 65, further comprising a digital communications interface.

68. A surgical device with a plurality of electrodes along a longitudinal surface of the device, each electrode operable to generate an electrical stimulation current to a tissue proximate to the electrode, if the tissue comprises a nerve within range of an electrode, the current causes an electromyographic (EMG) response in a muscle associated with the nerve.

69. The surgical device of claim 68, comprising a cannula.

70. The surgical device of claim 68, comprising a nerve root retractor.

71. A system comprising:

a pedicle screw test probe having at least one electrode, the electrode being configured to deliver an electrical current signal to a hole sized to fit a pedicle screw;

a sensor configured to sense a voltage response from a muscle caused by the electrical current signal; and

a control unit configured to compare the electrical current signal and the voltage response to determine if the pedicle hole has been breached.

72. The system of claim 71, wherein the pedicle screw test probe has a ball-tipped distal end.

73. A device configured to simulate a nerve and muscle in a patient, the device comprising:

a input connector configured to receive electrical current stimulation signals with a plurality of amplitude levels from an instrument;

a processing unit configured to derive pre-determined voltage response signals in response to the electrical current stimulation signals; and

an output connector configured to output voltage response signals in response to the electrical current stimulation signals.

74. A method of providing a nerve stimulation system, the method comprises:

providing a control unit; and

loading software in the control unit, the software being configured to initiate a stimulation current signal upon receiving a user command, monitor a voltage response signal after initiating the stimulation current signal, and determine a stimulation current for a pre-determined voltage response value.

75. The method of claim 74, further comprising setting a threshold voltage response value.

76. The method of claim 74, further comprising configuring a maximum stimulation current.

77. A method comprising:

delivering a plurality of electrical current signals near a tissue region;

sensing a plurality of electromyographic (EMG) voltage responses of a muscle associated with a nerve in the tissue region; and

identifying a relationship between amplitudes of the current signals and the EMG voltage responses.

78. The method of claim 77, further comprising determining a stimulation current for a predetermined threshold voltage response.

79. The method of claim 77, wherein identifying a relationship comprises bracketing a threshold stimulation current.

80. The method of claim 77, wherein identifying a relationship comprises bisecting a bracket containing a threshold stimulation current.

81. The method of claim 77, further comprising inserting an instrument with an electrode through tissue near a spine.

82. The method of claim 77, further comprising establishing an operative corridor through tissues having neural structure.

83. The method of claim 77, further comprising advancing a cannula toward a target site.

84. The method of claim 77, wherein the target site is an annulus of an intervertebral disc.

85. The method of claim 77, further comprising determining a threshold current by linear regression.

86. The method of claim 77, further comprising a dynamic sweep subtraction process.

87. The method of claim 77, further comprising displaying a decreasing threshold stimulation current as a stimulation electrode moves closer to a nerve.

88. The method of claim 77, further comprising displaying a name of an instrument being used to deliver the plurality of electrical current signals.

89. The method of claim 77, further comprising displaying locations of sensors sensing a plurality of electromyographic (EMG) voltage responses of muscles.

90. The method of claim 77, further comprising notifying a user to advance a surgical instrument delivering the plurality of electrical current signals.

91. The method of claim 77, further comprising notifying a user to hold a surgical instrument delivering the plurality of electrical current signals.

92. The method of claim 77, further comprising notifying a user when a nerve is impinged.

93. The method of claim 77, further comprising determining peak-to-peak voltage values of the EMG voltage responses of a muscle myotome in response to the plurality of electrical current signals applied to a nerve.

94. The method of claim 77, further comprising delivering electrical current signals as monophase pulses with a predetermined duration and configurable amplitudes.

95. The method of claim 77, further comprising delivering electrical current signals as monophase pulses with configurable durations and amplitudes.

96. The method of claim 77, further comprising displaying a voltage response vs. stimulation current recruitment curve.

97. The method of claim 77, further comprising measuring a first time duration from a stimulation current pulse to a first peak of a voltage response waveform.

98. The method of claim 97, further comprising measuring a second time duration from a stimulation current pulse to a second peak of a voltage response waveform.

99. The method of claim 98, further comprising collecting multiple samples of the first and second time durations.

100. The method of claim 98, further comprising compiling the first and second time durations in a histogram.

101. The method of claim 77, further comprising displaying a direction of a nerve based on the relationship between amplitudes of the current signals and the EMG voltage responses.

102. The method of claim 77, further comprising displaying a pathology of a nerve based on the relationship between amplitudes of the current signals and the EMG voltage responses.

103. The method of claim 77, further comprising retracting the nerve.

104. The method of claim 77, further comprising displaying a function of the nerve in real-time as a surgical instrument is moved with respect to the nerve.

105. The method of claim 77, further comprising sensing and displaying a function of the nerve in real-time during a surgical procedure.

106. The method of claim 77, further comprising testing a pedicle hole.

107. The method of claim 77, further comprising testing a screw in a pedicle hole.

108. The method of claim 77, further comprising determining whether a pedicle wall has been breached by the screw.

109. The method of claim 77, further comprising displaying a channel with a lowest response among a plurality of channels.

110. The method of claim 77, further comprising concurrently displaying voltage waveforms of a plurality of electromyographic (EMG) responses from a plurality of sensors.