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

1. A method of using a surgical access system for accessing a spinal target site, comprising:

inserting an inner dilator of a plurality of spinal access dilators of the surgical access system along a selected access path between a skin penetration site and a targeted intervertebral disc, the surgical access system comprising:

the plurality of spinal access dilators adapted to bluntly dissect bodily tissue along the selected access path between the skin penetration site and the targeted intervertebral disc, each of the spinal access dilators comprising a central lumen extending from a proximal end to a distal opening at a distal tip region and a longitudinal length sufficient to extend from said targeted intervertebral disc to a location external to said skin penetration site, the plurality of spinal access dilators comprising the inner dilator and an outer dilator configured to advance over the inner dilator, at least the inner dilator comprising an outer diameter of 6 mm to 30 mm and the distal tip region of the inner dilator defining four generally orthogonally disposed stimulation electrode positions arranged annularly about a central axis of the distal opening of said inner dilator, and an electrode at any of said four generally orthogonally disposed stimulation electrode positions is configured to individually output a stimulation signal for nerve monitoring;

an electrical stimulation conductor adapted to transmit said stimulation signal from a nerve monitoring; system, wherein said electrical stimulation conductor is configured to releasably engage with at least said inner dilator to output said stimulation signal for nerve monitoring

an elongate penetration member configured to slidingly engage along the central lumen of the inner dilator, wherein the elongate penetration member has a distal tip configured to penetrate an annulus of said targeted intervertebral disc; and

an operative corridor instrument that is deliverable over an outermost dilator of said spinal access dilators;

while the inner dilator is located in the selected access path between the skin penetration site and the targeted intervertebral disc, using the electrical stimulation conductor to transmit said stimulation signal from the nerve monitoring system to said bodily tissue along the selected access path, wherein the nerve monitoring system delivers the stimulation signal to the electrode at any of said four generally orthogonally disposed stimulation electrode positions, monitors electromyographic activity detected by a set of sensor electrodes in leg muscle myotomes associated with nerves in the vicinity of the targeted intervertebral disc, and then contemporaneously displays on a display screen both: a graphic representation of locations of said leg muscle myotomes, and a numeric stimulation threshold in units of milliAmps required to obtain the electromyographic activity in at least one of said leg muscle myotomes;

after inserting the inner dilator to the targeted intervertebral disc, docking the elongate penetration member within the targeted intervertebral disc by sliding the elongate penetration member in the central lumen of the inner dilator so that the distal tip of the elongate penetration member extends distally from the inner dilator and penetrates the annulus of said targeted intervertebral disc;

after docking the elongate penetration member within the targeted intervertebral disc, advancing the outer dilator over the inner dilator and along the selected access path toward the targeted intervertebral disc;

slidably advancing an operative corridor instrument over the outermost dilator along the selected access path toward the targeted intervertebral disc; and

removing the plurality of spinal access dilators from the operative corridor instrument to establish a corridor along the selected access path between the skin penetration site and the targeted intervertebral disc.

2. The method of claim 1 , wherein the operative corridor instrument comprises a working cannula that defines a tubular corridor to access the targeted intervertebral disc when the working cannula is advanced to the targeted intervertebral disc.

3. The method of claim 1 , wherein said electrode at any of said four generally orthogonally disposed stimulation electrode positions is configured to emit said stimulation signal in a monopolar configuration.

4. The method of claim 1 , wherein the nerve monitoring system contemporaneously displays: said graphic representation of locations of said leg muscle myotomes, said numeric stimulation threshold in units of milliAmps required to obtain the electromyographic activity in at least one of said leg muscle myotomes, and an indication of nerve direction relative to inner dilator.

5. The method of claim 4 , wherein the nerve monitoring system displays numeric stimulation threshold in units of milliAmps along with a color code indicative of a degree of nerve proximity.

6. The method of claim 1 , wherein said electrical stimulation conductor comprises a clip device.

7. The method of claim 1 , further comprising connecting a stimulation driver device with said electrical stimulation conductor, the stimulation driver including one or more actuators for selectively activating said stimulation signal for transmission through the electrical stimulation conductor.