Fiducial-free 2D/3D registration of the proximal femur for robot-assisted femoroplasty

Abstract

Femroplasty is a proposed therapeutic method for preventing osteoporotic hip fractures in elderly. Patientspecific femoroplasty based on a preoperative plan, however, requires accurate 3D pose estimation of the proximal femur. Prior work on the development of a navigation system required the attachment of an optical fiducial to the osteoporotic femur. In this paper, we propose a fiducial-free 2D/3D registration pipeline, which uses the pelvis to initialize the femur registration. Intraoperative X-ray images are taken from multiple views to perform compound object registration. The proposed method was tested through a comprehensive simulation study. Performance was evaluated on the femoral head center frame registration error and the injection entry point error on the trochanter surface. The algorithm achieved a mean accuracy of 2.75 ± 2.19 mm for the entry point ℓ₂ distance and 0.81 ± 0.58° for the planning path direction, which is sufficiently accurate for robotic drill positioning.