Electromyography system
A method of determining relative neuro-muscular response onset value thresholds for a plurality of spinal nerves, comprising: depolarizing a portion of the patient's cauda equina; and measuring the current intensity level at which a neuro-muscular response to the depolarization of the cauda equina is detected in each of the plurality of spinal nerves. A method for detecting the presence of a nerve adjacent the distal end of at least one probe, comprising: determining relative neuro-muscular response onset values for a plurality of spinal nerves; emitting a stimulus pulse from a probe or surgical tool; detecting neuro-muscular responses to the stimulus pulse in each of the plurality of spinal nerves; and concluding that the electrode disposed on the distal end of the at least one probe is positioned adjacent to a first spinal nerve when the neuro-muscular response detected in the first spinal nerve is detected as a current intensity level less than or equal to a corresponding neuro-muscular response onset value of the first spinal nerve.
1 . A system for determining the proximity of a nerve during surgical access to a spinal target site, comprising:
an instrument configured for advancement through the body tissue of a patient and equipped with an electrode situated near a distal end of said instrument for emitting a stimulation signal of know intensity through while advancing said instrument to said target site;
a stimulator for delivering said stimulation signal to said electrode;
an adjuster for varying the intensity of the stimulation signal generated by said stimulator for delivering to said body tissue through said electrode;
at least one sensor positioned at least one of within and near a myotome for detecting a neuro-muscular response evoked by said stimulation signal;
a signal processor in communication with said sensor for processing said neuro-muscular response and communicating said processed signal to a controller;
a controller in communication with said stimulator and said signal processor, said controller configured to compare the stimulation intensity level at which a neuro-muscular response was detected to a predetermined stimulation intensity level to indicate the relative proximity of said spinal nerve to said distal end of said instrument; and
a communicator for communicating the relative proximity determined by the controller to a user.
2 . The system of claim 1 , wherein said instrument is a surgical probe.
3 . The system of claim 1 , wherein said instrument is a surgical access instrument.
4 . The system of claim 4 , wherein said instrument is a cannula.
5 . The system of claim 1 , wherein said stimulator may vary at least one of the pulse frequency and pulse duration of the stimulation signal.
6 . The system one of claim 1 , wherein the adjuster is configured to adjust the intensity level of the stimulation signal until said neuro-muscular response is detected.
7 . The system of claim 6 , wherein the adjuster is configured to allow incremental adjustments of the stimulation signal.
8 . The system of claim 1 , wherein said communicator is configured to at least one of visually and audibly indicating to said user the relative proximity of a nerve to said distal end of said instrument.
9 . The system of claim 8 , wherein said communicator includes at least one LED.
10 . The system of claim 8 , wherein said communicator includes an LCD screen.
11 . The system of claim 1 , wherein said communicator is implemented individually.
12 . The system of claim 8 , wherein said communicator sounds an alarm to indicate the relative proximity determined.
13 . The system of claim 12 , wherein the volume of the alarm is varied depending on the relative proximity determined.
14 . The system of claim 12 , wherein the frequency of the alarm is varied depending on the relative proximity determined.
15 . The system of claim 8 , wherein the communicator displays a color to indicate the relative proximity determined.
16 . The system of claim 15 , wherein the color is varied depending on the relative proximity of the nerve detected.