• augmented reality
• CAS
• computer assisted surgery
• image guided surgery
• navigation system
• pelvic organ prolapse
• robotic surgery
• sacrocolpopexy

This study introduces a navigation system designed for robotic sacrocolpopexy, aimed to identify hidden critical vessels at the mesh anchoring site by displaying an AR virtual image consistent with the real endoscopic view.
Stereo endoscope is used as a locator, avoiding the need for other external technologies, and virtual anatomy is obtained from preoperative CT scan, avoiding intraoperative ionising radiations.
The navigation system relies on anatomical landmarks, specifically the two round ligament insertions in the inguinal canal, visible in the operative scene and stable during insufflation because close to the edge of the pelvis. From the analysis of CT images, it was also confirmed that these two points are identifiable in preoperative images, at least in patients with medium and high BMI, who are the main beneficiaries of this surgical case. However, using only two landmarks isn’t adequate for finding the registration matrix between two reference systems (endoscope and CT images), since a degree of freedom remains unconstrained.
To fix the lacking angle, the pubic symphysis is used as an anatomical bone landmark. It is not visible from cameras, so an external rod is introduced as a mechanical constraint: anchored to the endoscope and rested on the symphysis, made of two parts with a joint to fit to all patients. It is fixed to the endoscope but easily removable while the endoscope is inserted, to clear the space after the critical site is selected. The overlap of virtual anatomy with real endoscope scene is achieved using corresponding point alignment and minimum distance between the rod and the virtual symphysis
The developed system is evaluated on a patient specific phantom, which includes bony and vascular structures in the pelvis area.