Design of a positioning system for orienting surgical cannulae during Minimally Invasive Spine Surgery

This paper presents the design of a surgical positioning system conceived to handle and orient a cannula for Minimally Invasive Spine Surgery (MISS) keeping fixed a remote center of rotation during the orientation procedure. Specifically, many MISS treatments require the use of a transpedicular cannula as a guiding tool for spine fixation or for delivering biomaterials to the vertebral body or to the disc space. We designed a cannula orientation mechanism able to percutaneously guide the insertion towards the intervertebral space based only on the acquisition of a few fluoroscopic images. The insertion orientation, and therefore the regulation of the system joints configuration, can be planned by a software based on two perpendicular C-arm fluoroscopic images and starting from the identification of the insertion point and of the insertion direction drawn on the images by the surgeon. We present the software for the orientation planning and a simple kinematic structure with remote center of motion that allows the positioning and orientation of the guiding cannula. The system was dimensioned so to be compatible with the size of C-arm workspace and to minimally interfere with the surgical procedure and with the work of the medical staff.