Electromagnetic Navigation for Femoral Osteotomy Using High-Accuracy X-ray-to-CT Registration

2026-06-02

AI Summary

This study addresses the challenges in femoral osteotomy surgery, where preoperative plans are difficult to execute accurately due to insufficient precision, high invasiveness of existing techniques, and excessive intraoperative radiation exposure. To overcome these limitations, the authors propose a novel approach that integrates preoperative CT-based planning with a high-precision rigid X-ray-to-CT registration method requiring only two intraoperative X-ray images, combined with electromagnetic tracking for fluoroscopy-free real-time navigation. Leveraging a one-time C-arm calibration, the method achieved a mean total angular error of 3.05° across 18 synthetic femur experiments—significantly outperforming freehand execution (6.32°) and consistently remaining below the 5° clinical acceptability threshold. The accuracy rivals that of patient-specific instrumentation while substantially reducing both radiation exposure and surgical invasiveness.

Abstract

Accurate execution of preoperative plans in corrective femoral osteotomies remains challenging. Current techniques are limited by variable accuracy, invasiveness, and radiation exposure, with free-hand methods and patient-specific instrumentation (PSI) often requiring >30 and >6 fluoroscopic images, respectively. We present an integrated, electromagnetic tracking (EMT)-based navigation system for femoral osteotomies that minimizes dissection and intraoperative fluoroscopy. The system couples CT-based preoperative planning with one-time intraoperative C-arm calibration and accurate X-ray-to-CT registration from two fluoroscopic images acquired at initialization. This enables real-time, fluoroscopy-free EMT navigation of the saw blade and bone fragments relative to the preoperative plan, and is compatible with uniplanar and biplanar osteotomies. In a feasibility study using 18 synthetic femora, EMT guidance significantly outperformed free-hand execution in total angular error ($(3.05 \pm 0.75)^\circ$ vs.\ $(6.32 \pm 2.36)^\circ$, $p=0.031$), assuming the same minimal surgical exposure for both. No EMT-guided trials exceeded the >5° clinical threshold, whereas free-hand produced 4 outliers of 6 trials. 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. By transferring preoperative plans using only two fluoroscopic images while matching PSI accuracy without additional surgical exposure, the proposed system motivates subsequent cadaveric and clinical validation.

Problem

• femoral osteotomy
• preoperative planning
• fluoroscopy reduction
• surgical accuracy
• electromagnetic navigation

Innovation

• electromagnetic tracking
• X-ray-to-CT registration
• femoral osteotomy
• fluoroscopy-free navigation
• preoperative planning