  In percutaneous orthopedic interventions the surgeon attempts to reduce and
fixate fractures in bony structures. The complexity of these interventions
arises when the surgeon performs the challenging task of navigating surgical
tools percutaneously only under the guidance of 2D interventional X-ray
imaging. Moreover, the intra-operatively acquired data is only visualized
indirectly on external displays. In this work, we propose a flexible Augmented
Reality (AR) paradigm using optical see-through head mounted displays. The key
technical contribution of this work includes the marker-less and dynamic
tracking concept which closes the calibration loop between patient, C-arm and
the surgeon. This calibration is enabled using Simultaneous Localization and
Mapping of the environment of the operating theater. In return, the proposed
solution provides in situ visualization of pre- and intra-operative 3D medical
data directly at the surgical site. We demonstrate pre-clinical evaluation of a
prototype system, and report errors for calibration and target registration.
Finally, we demonstrate the usefulness of the proposed inside-out tracking
system in achieving "bull's eye" view for C-arm-guided punctures. This AR
solution provides an intuitive visualization of the anatomy and can simplify
the hand-eye coordination for the orthopedic surgeon.
