2D-3D reconstruction-based implant migration measurement

This paper presents a phantom-based study for validating a newly developed 2D-3D reconstruction-based method for measuring implant migration after total hip arthroplasty (THA). Based on a mock-up setup, three different methods were used to determine the cup orientation with respect to the anterior pelvic plane (APP) of a plastic pelvis: (a) the optical tracking method; (b) the fiducial-based method; and (c) the 2D-3D reconstruction-based method. It was found that the incremental anteversion and inclination angles measured by the newly developed 2D-3D reconstruction-based method are comparable with those measured by the other two methods. 1 Background The initial and the secondary implant positions after the cementless total hip arthroplasty (THA) documents the stability of the implanted components. Postoperative migration of implants is therefore one important parameter for initial and follow-up quality documentation. Due to the concerns on cost and radiation, postoperative migration is typically measured on two-dimensional (2D) postoperative anteroposterior (AP) pelvic X-ray radiographs. The existing methods either determine only a 2D migration in the AP pelvic X-ray radiograph plane [2] or require invasive implantation of metal fiducials to determine precise three-dimensional (3D) migration [1]. Recently, a precise X-ray image calibration method as well as a 2D-3D reconstruction method has been reported for a robust and accurate reconstruction of a 3D patient-specific model of acetabular surface from 2D X-ray radiographs [3]. However, there is little known work reported to use 2D-3D reconstruction for implant migration measurement. The aim of this work is to determine the incremental orientation variation of a cup implant using 2D-3D reconstruction techniques and to validate the methodology using optical tracking and implanted metal fiducials. 2 Materials and Methods Mockup setup: First a mockup was built that allowed simulating cup migration with respect to a fixed pelvis. The mockup was composed of a cadaver pelvis that was not part of the statistical shape model (SSM) population but represented by it (male, caucasian), a plastic cup and a fixation frame made from X-ray translucent Plexiglas. The construction allowed the cup to move on a spherical joint by hand and to hold the position during acquisition, while the pelvis was fixed permanently to the frame (see figure 1). Four metal markers where placed coplanar with the cup opening plane. The placement was designed to provide reliable landmarks in the X-ray images. Furthermore ten metal nails with indents that allowed pointer tool picking were placed on the pelvis to mark the …