Smart trail with camera and inertial measurement unit for intraoperative estimation of hip range of motion in total hip replacement surgery

To minimize the risk of prosthetic impingement after total hip replacement (THR), a novel smart trial is proposed for intraoperative estimation of hip range of motion (ROM) in THR surgery. The smart trial is used to examine the stability, range of motions and risk of dislocation during the surgery, relocate hip implants, and finally will be replaced by real implant prosthesis. The smart trial is composed of a customized femoral head trial with a camera and an inertial measurement unit (IMU) inside, and a customized acetabular cup trial with reference patterns printed on the internal surface. A depth estimation algorithm based on images taken by the camera is designed for the detection of critical regions where impingement or dislocation is about to happen, and an extended Kalman filter is designed for the fusion of the data from IMU to acquire better orientation estimation accuracy. This paper is proof of concept with limited validation through an experimental setup. Simulation results show that the root mean square error (RMSE) of the depth estimation is 1mm and that of the orientation estimation is less than 0.05 degree. The hip ROM is displayed in 3-D mode in real time.