Measurement System for Attitude of Anterior Pelvic Plane and Implantation of Prothesis in THR Surgery

With the average age of population increasing in the world, the number of total hip replacement (THR) surgeries increases year by year. However, the failure rate of THR surgeries is up to 10% following primary surgery and 28% after revision arthroplasty, which has direct correlation to the implantation angles between prosthesis and pelvis. To improve the implanting accuracy of the prosthesis, we propose a measurement system and estimation algorithms. The system includes three parts: an initial attitude measurement instrument, which is used to determine the initial attitude of the anterior pelvic plane (APP), a real-time attitude measurement instrument, which aims to acquire the real-time attitude of the APP, and an acetabular cup angle measurement instrument, which obtains the relative angles between prosthesis and pelvis. Each of them is based on inertial measurement unit (IMU) and magnetometer. A quaternion-based extended Kalman filter is adopted to fuse the data from IMU and magnetometer to estimate the orientation, and the algorithm calculating the attitude of pelvis and relative angles between pelvis and prosthesis is designed in this paper. The reliability of this system, from the measurement point of view, has been verified by experiments. The experimental results show that the root-mean-square errors of APP attitude and acetabular cup implanting orientation are less than 1.6° and 3° with standard uncertainty of less than 0.22° and 0.17°, respectively. The accuracy of our system meets the requirement of the THR surgeries.