Dilation system and method of using the same

A method of forming an access opening through a psoas muscle to a patient's spine, comprising:

• (a) laterally inserting a stimulating probe into the psoas muscle, the stimulating probe having a probe axis and a probe tip;
• (b) transmitting an electrical pulse into the stimulating probe to locate a safe zone in the psoas muscle;
• (c) laterally inserting the stimulating probe through the psoas muscle so the probe tip is proximate the patient's spine;
• (d) obtaining first directional dilator having a first longitudinal axis, a first bore having a length extending from a proximal end to a distal end of the first directional dilator, a first bore axis that is offset from the first longitudinal axis, and a first channel formed in an outer surface of the first directional dilator so as to be in communication with the first bore along at least a portion of the length of the first bore;
• (e) inserting the first directional dilator through the psoas muscle and toward the patient's spine guided by sliding engagement of the stimulating probe with the first bore of the first directional dilator and a portion of the stimulating probe extending into the first channel with the stimulating probe positioned between the nerve and the longitudinal axis of the first directional dilator;
• (f) obtaining a second directional dilator having a second longitudinal axis, a second bore having a length extending from a proximal end to a distal end of the second directional dilator, a second bore axis that is offset from the second longitudinal axis, and a second channel formed in an outer surface of the second directional dilator so as to be in communication with the second bore along at least a portion of the length of the second bore;
• and
• (g) inserting the second directional dilator through the psoas muscle toward the patient's spine guided by sliding engagement of the first directional dilator with the second bore of the second directional dilator and a portion of the first directional dilator extending into the second channel with the first directional dilator positioned between the nerve and the second longitudinal axis of the second directional dilator.