  Periacetabular osteotomy is a challenging surgical procedure for treating
developmental hip dysplasia, providing greater coverage of the femoral head via
relocation of a patient's acetabulum. Since fluoroscopic imaging is frequently
used in the surgical workflow, computer-assisted X-Ray navigation of osteotomes
and the relocated acetabular fragment should be feasible. We use
intensity-based 2D/3D registration to estimate the pelvis pose with respect to
fluoroscopic images, recover relative poses of multiple views, and triangulate
landmarks which may be used for navigation. Existing similarity metrics are
unable to consistently account for the inherent mismatch between the
preoperative intact pelvis, and the intraoperative reality of a fractured
pelvis. To mitigate the effect of this mismatch, we continuously estimate the
relevance of each pixel to solving the registration and use these values as
weightings in a patch-based similarity metric. Limiting computation to randomly
selected subsets of patches results in faster runtimes than existing
patch-based methods. A simulation study was conducted with random fragment
shapes, relocations, and fluoroscopic views, and the proposed method achieved a
1.7 mm mean triangulation error over all landmarks, compared to mean errors of
3 mm and 2.8 mm for the non-patched and image-intensity-variance-weighted patch
similarity metrics, respectively.
