  Fluoroscopic X-ray guidance is a cornerstone for percutaneous orthopaedic
surgical procedures. However, two-dimensional observations of the
three-dimensional anatomy suffer from the effects of projective simplification.
Consequently, many X-ray images from various orientations need to be acquired
for the surgeon to accurately assess the spatial relations between the
patient's anatomy and the surgical tools. In this paper, we present an
on-the-fly surgical support system that provides guidance using augmented
reality and can be used in quasi-unprepared operating rooms. The proposed
system builds upon a multi-modality marker and simultaneous localization and
mapping technique to co-calibrate an optical see-through head mounted display
to a C-arm fluoroscopy system. Then, annotations on the 2D X-ray images can be
rendered as virtual objects in 3D providing surgical guidance. We
quantitatively evaluate the components of the proposed system, and finally,
design a feasibility study on a semi-anthropomorphic phantom. The accuracy of
our system was comparable to the traditional image-guided technique while
substantially reducing the number of acquired X-ray images as well as procedure
time. Our promising results encourage further research on the interaction
between virtual and real objects, that we believe will directly benefit the
proposed method. Further, we would like to explore the capabilities of our
on-the-fly augmented reality support system in a larger study directed towards
common orthopaedic interventions.
