A tissue retractor system includes first and second arms extending from a support assembly, and third and fourth arms extending from a support mechanism. Each arm includes a proximal span, a distal span, and a blade support between the proximal span and distal span. The retractor system features retractor units that can be used independently or in a nested arrangement. The system also includes instruments for inserting a spinal rod. A method for implanting a spinal rod through an incision includes the steps of inserting the spinal rod through a dividable tube, turning the rod subcutaneously toward a rod receiving anchor and advancing the rod subcutaneously toward the rod receiving anchor.