A method of performing a computer-assisted surgical procedure on the spine of a patient comprising the steps of: planning, on a computer, a surgical procedure based on at least one of two- and three-dimensional images of the patient's spine; affixing a robotic assembly over an operative region of the patient; determining, with a computer in communication with the robotic assembly, a desired trajectory of a surgical tool along at least one of an access path and an implant path towards the surgical target site; and placing at least a portion of the surgical tool through the aperture along said desired trajectory along at least one of said access path and said implant path towards the surgical target site.