Electromagnetic navigation for femoral osteotomy using high-accuracy X-ray-to-CT registration

Accurate execution of preoperative plans in corrective femoral osteotomies remains a substantial challenge. Current techniques are limited by variable accuracy, invasiveness, and substantial radiation exposure, with free-hand methods and patient-specific instrumentation (PSI) often requiring $>30$ and $>6$ fluoroscopic images, respectively. This work addresses the need for an accurate navigation system that minimizes dissection and intraoperative fluoroscopy.

We present an integrated, electromagnetic tracking (EMT)-based navigation system for femoral osteotomies. The system couples CT-based preoperative bone planning with one-time intraoperative C-arm calibration and accurate X-ray-to-CT registration, based on two fluoroscopic images acquired at initialization. This registration is followed by real-time, fluoroscopy-free EMT-based navigation of the sawblade, and subsequently of the bone fragments, with respect to the preoperative plan, and is compatible with uniplanar and biplanar osteotomies.

In a feasibility study utilizing 18 synthetic femora, EMT guidance significantly outperformed free-hand execution for total angular error ( ${(3.05\pm 0.75)}^{\circ }$ vs. ${(6.32\pm 2.36)}^{\circ }$ , $p=0.031$ ). No EMT-guided trials exceeded the $5^{\circ }$ clinical threshold, whereas free-hand resulted in 4 outliers out of 6 trials while assuming the same full surgical exposure for both techniques. The system achieved statistical equivalence ( $\pm 2^{\circ }$ , $\pm 2\text{mm}$ ) to PSI for total angular ( $p\le 0.02$ ) and total translational ( $p=0.048$ ) errors with no significant differences in user questionnaire scores.

The proposed EMT-based system enables transfer of preoperative plans to the OR using two fluoroscopic images and provides real-time intraoperative guidance. In a synthetic bone feasibility study, it substantially improved correction accuracy over free-hand execution and achieved equivalent accuracy to PSI, while no additional surgical exposure is needed and requiring substantially fewer fluoroscopic images, motivating subsequent cadaveric and clinical validation.