Ultrasound-Based Robot-Assisted Drilling for Minimally Invasive Pedicle Screw Placement

Minimally invasive pedicle screw placement (MIPSP) is a widely used treatment for spine diseases. When coupled with intraoperative navigation modalities, robots may help improve surgical outcomes and reduce complications. With such a system, the application of pedicle screws has been expanded from needle insertion to the spine surgery. This paper investigates the possibility and feasibility of robot-assisted MIPSP based on ultrasound (US) guidance. The proposed system is non-radiative and fiducial-free, using purely image information to close the registration loop. Then the system automatically positions the drill tip to a planned screw trajectory and executes the drilling operation. Experiments were conducted on both ex-vivo lamb and human cadaver spines. An entry point accuracy of $2.39\pm 1.41$ mm, and orientation accuracy of $2.82\pm 1.85^{\circ }$ was found for 24 drilled trajectories on three lamb spines. On the ex-vivo human spine, the position error averaged $3.08\pm 2.43$ mm at the entry point and $4.05\pm 2.62$ mm at the stop point across 16 drilling instances. Moreover, a $87.5\%$ success rate was reported by using Gertzbein-Robbins grade. The experimental results demonstrate the potential for offering a radiation-free alternative. Although restricted to cadaver trials, this work encourages further exploration of this technology to assist surgeons in maximizing performance in clinical practice.

I. Introduction

Minimally invasive pedicle screw placement (MIPSP) is a common step for posterior fixation in spinal surgery because of its biomechanical superiority and ability to offer significant corrections to the spine [1]. It also leads to reduced revision rates, lower infection rates, shorter hospital stays, and considerable economic benefits compared to the non-minimally invasive case. However, MIPSP still faces challenges such as limited visibility and poor tissue discrimination. Inaccurate pedicle screw placement (PSP) may lead to neurological impairment such as pain, weakness or sensory loss. Screw placement is an error-prone and time-consuming step of MIPSP when performed manually [2]. Great care needs to be demonstrated in this procedure, as screw placement accuracy is paramount and critical for a successful surgery [3].