[Electromagnetic navigation of transpedicular punctures: more precise than the standard?]

Before clinical implementation of an approved electromagnetic tracking system (CAPPA IRAD EMT) an experimental trial was performed to investigate the accuracy of the system and its safety in application for transpedicular vertebral punctures in comparison to the classical fluoroscopic method.

A total of 110 transpedicular punctures were performed bilaterally using 11 vertebrae of 5 realistic artificial phantoms and 1 pedicle was punctured with the conventional technique using c-arm fluoroscopy and the other with the electromagnetic tracking system. As a target a radiopaque non-ferromagnetic marker was implanted bilaterally in the anterior wall of the vertebrae. For evaluation of the precision the distance from the end of the puncture to the target and the gradual deviation of the actual channel from the ideal trajectory were assessed in three-dimensional computer tomography. Calculations and statistical analysis were performed according to the Wilcoxon test by means of SPSS 16.0.1 for Windows.

The mean distance from the target was 6.6 mm (± 3.9 mm standard deviation SD) with electromagnetic navigation compared to 3.2 mm (± 2.8 mm SD) with fluoroscopic assistance and the mean aberration from the ideal trajectory was 18.4° (± 4.6° SD) compared to 6.5° (± 3.5° SD), respectively. The difference of accuracy was highly significant regarding both parameters (p < 0.001).

The minimum requirement for accuracy of transpedicular punctures could not be achieved with electromagnetic navigation. Unless proven otherwise, the lack of accuracy is attributed to unstable referencing. Despite evidence of successful employment for soft tissue punctures the system cannot currently be recommended for osseous applications of the spine.