Multi-body 3D-2D registration for image-guided reduction of pelvic dislocation in orthopaedic trauma surgery.

PURPOSE: Surgical reduction of pelvic dislocation is a challenging procedure with poor long-term prognosis if natural morphology is not accurately restored. The procedure often requires long fluoroscopic exposure times and trial-and-error to achieve accurate reduction. We report a method to automatically compute the target pose of dislocated bones from preoperative CT and provide 3D guidance of reduction using routine 2D fluoroscopy.

METHOD: A pelvic statistical shape model (SSM) and a statistical pose model (SPM) were formed automatic bone segmentation and estimation of dislocated bone target pose. Intraoperatively, 3D pose of multiple bones were obtained via 3D-2D registration to fluoroscopy images. The method was examined in three studies: a simulation, a phantom, and a clinical case study. Algorithm sensitivity to capture range, radiation dose, and field of view (FOV) size were investigated.

RESULTS: The simulation study achieved target pose estimation with translational error of median 2.3 mm (1.4 mm IQR) and rotational error of 2.1° (1.3° IQR). 3D-2D registration yielded 0.3 mm (0.2 mm IQR) in-plane and 0.3 mm (0.2 mm IQR) out-of-plane translational error, with capture range of ±50 mm and ±120 mm, respectively. The phantom study demonstrated 3D-2D target registration error of 2.5 mm (1.5 mm IQR) with robustness over dose range down to 5 μGy/frame (10% of the nominal fluoroscopic dose). The clinical case yielded 3.1 mm (1.0 mm IQR) projection distance error with robust performance for square FOV ranging 340-170 mm².

CONCLUSION: The method demonstrated accurate target reduction pose estimation in simulation, phantom, and clinical feasibility study for a broad range of dislocation patterns, initialization error, dose levels, and FOV size. The system provides a novel means of guidance and assessment of pelvic reduction from routinely acquired images. The method has the potential to reduce radiation dose and guide more accurate joint dislocation reductions.