A Smart Registration Assistant for Joint Replacement: Concept Demonstration

Abstract

In robot-assisted orthopaedic surgery, registration is a key step, which defines the position of the patient in the robot frame so that the preoperative plan can be performed. Current registration methods have their limitations, such as the requirement of immobilising the limb or maintaining the line of sight (LOS). These issues cause inconvenience for the surgeons and interrupt the surgical workflow in the operating room.Targeting these issues, we propose a smart camera-robot registration system for joint replacement. The bone geometry, which is measured directly by a depth camera, is aligned to a preoperatively obtained bone model to calculate the pose of the target. Simultaneously, in order to avoid registration failure caused by LOS disruptions, the depth camera tracks objects that may occlude the target bone, and a robot manipulator is used to move the camera away from the nearest obstacle. An appropriate camera motion to “escape” the obstacle is calculated based on the position and velocity of the obstacle, with the aim of avoiding the occlusion efficiently without changing the general target position in the camera frame. The inverse kinematics of the robot is used to project the Cartesian velocity of the end-effector into the joint space, with kinematic singularities considered for stable robotic control. An admittance controller is designed as the human-robot interface so that the surgeon can directly set the robot configuration by hand according to a given intraoperative scenario.Simulations and experiments with a redundant manipulator were conducted to test the performance of a proof-of-concept implementation. The results show that the proposed obstacle avoidance method can effectively increase the distance between the obstacle and the LOS, which lowers the risk of registration failure due to obstacle occlusion. This pilot study is promising in reducing distractions to the surgeon and could help achieve a fluent and surgeon-centred workflow.