CT-less three-dimensional fluoroscopic navigation for femur head surgery

Objectives/Background: The surface of the femur head is nearly spherical due to the biomechanical function of the joint. Specifically, given the nearly spherical shape of the joint adjacent portion of the femur head, we can obtain a fully three-dimensional reconstruction and navigation technique that does not require any intra-operative registration. Although the surface of the femur is well visible in fluoroscopic images, it is often confusing that the surface visible in the fluoroscopic projection does not correspond to the real surface for arbitrary drilling direction. A simple geometric observation reveals that the error in this direct surface estimation can be more than a centimeter. DesigdMetbods: Our technique extracts two circles from projection images, then computes the true placement of the spherical portion of the femur head surface, and displays the distance from the surface during navigation. Results/Conclusions: We consider the following indications: (I) placement of stabilizing wires in the femur head, and (2) removal of small osteo-necrotic lesions near the femur surface. Since patients in both cases are often children, CT tomography could be considered problematic due to radiation exposure. Furthermore, even if tomographic images are available, their intra-operative registration is difficult and time-consuming. Experiments with anatomical specimens have been carried out to determine the overall accuracy of this exceedingly simple yet precise navigation technique for femur head surgery.