Electromagnetically tracked personalized templates for surgical navigation

Abstract

Purpose

An electromagnetic (EM) surgical tracking system was developed for orthopedic navigation. The reportedly poor accuracy of point-based EM navigation was improved by using anatomical impressions, which were EM-tracked personalized templates. Lines, rather than points, were consistently used for calibration and error evaluation.

Methods

Technical accuracy was tested using models derived from CT scans of ten cadaver shoulders. Tracked impressions were first designed, calibrated, and tested using lines as fiducial objects. Next, tracked impressions were tested against EM point-based navigation and optical point-based navigation, in environments that were either relatively empty or that included surgical instruments. Finally, a tracked impression was tested on a cadaver forearm in a simulated fracture-repair task.

Results

Calibration of anatomical impressions to EM tracking was highly accurate, with mean fiducial localization errors in positions of 0.3 mm and in angles of \(0.6^\circ \) . Technical accuracy on physical shoulder models was also highly accurate; in an EM field with surgical instruments, the mean of target registration errors in positions was 2.2 mm and in angles was \(3.7^\circ \) . Preclinical accuracy in a cadaver forearm in positions was 0.4 mm and in angles was \(7.1^\circ \) . The technical accuracy was significantly better than point-based navigation, whether by EM tracking or by optical tracking. The preclinical accuracy was comparable to that achieved by point-based optical navigation.

Conclusions

EM-tracked impressions—a hybrid of personalized templates and EM navigation—are a promising technology for orthopedic applications. The two technical contributions are the novel hybrid navigation and the consistent use of lines as fiducial objects, replacing traditional point-based computations. The accuracy improvement was attributed to the combination of physical surfaces and line directions in the processes of calibration and registration. The technical studies and preclinical trial suggest that EM-tracked impressions are an accurate, ergonomic innovation in image-guided orthopedic surgery.

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