Cannula-Mounted Robots for Semi-Autonomous Vertebroplasty: A Comparison of Piezo-Based and Screw-Based Inchworm Drive Designs

Vertebral compression fractures are estimated to affect over 200 million people globally. Percutaneous vertebroplasty is a widely accepted minimally invasive treatment, but it has limitations including prolonged radiation exposure for providers and a steep learning curve. To address these challenges, we present two cannula-mounted robot designs for semi-autonomous, high-precision cannula insertion. Both designs are based on an inchworm mechanism, with one using an amplified piezoelectric actuator and the other using a linear actuator inspired approach. Each design is designed to generate at least 150 N of thrust force with submillimeter accuracy to reliably insert the cannula into the vertebral body. Finite element analysis shows that the material deformations of the baseplates, 42 ± 12 μm for the piezo inchworm design and 7.7±3.2 μm for the screw inchworm design, are substantially lower than the corresponding stroke lengths, confirming the feasibility of generating linear motion. An in silico imaging trial reveals the screw inchworm design's 44.4% smaller surgical footprint enables superior cannula insertion trajectory visualization compared to the piezo inchworm design. These results indicate that while both designs meet clinical design requirements for cannula insertion, the screw inchworm robot is better suited for a semi-autonomous approach to vertebroplasty.