Minimizing electromagnetic interference from surgical instruments on electromagnetic surgical navigation.
BACKGROUND
Electromagnetic computer-assisted surgery (EM-CAS) can be affected by various metallic or ferromagnetic factors.


OBJECTIVE
We determined to what extent metals interfere with accuracy and identified measures to prevent interference from occurring.


METHODS
Using an EM-CAS system, we made six standard measurements of tibiofemoral position and alignment on a surrogate knee. A stainless steel mallet was positioned 10 cm from the stylus, and then 10 cm from the localizer to create errors attributable to electromagnetic interference. The experiment was repeated with bars of different metals placed 10 cm from the stylus.


RESULTS
The maximum errors recorded with a mallet were: varus/valgus alignment, -2.7 degrees and 2.4 degrees; flexion/extension, -5.8 degrees and 3.0 degrees; lateral resection level, -3.1 and 7.5 mm; and medial resection level, -4.0 and 2.3 mm, respectively. The smallest errors were recorded with cylinders of titanium, cobalt-chrome alloy, and stainless steels. When moved more than 10 cm away from the stylus, errors became negligible.


CONCLUSIONS
The accuracy of EM navigation systems is affected substantially by the size, type, proximity, and shape of metal objects.


CONCLUSIONS
Stainless steel objects, such as cutting blocks and trial prostheses, should be kept more than 10 cm from EM-CAS instruments to minimize error.
Stevens
Faustin
F
Baylor College of Medicine, Houston, TX, USA.
Conditt
Michael A
MA
Kulkarni
Nikhil
N
Ismaily
Sabir K
SK
Noble
Philip C
PC
Lionberger
David R
DR
D016477:Artifacts; D004574:Electromagnetic Fields / Q000009:adverse effects*; D005269:Femur / Q000033:anatomy & histology; D006801:Humans; D021621:Imaging, Three-Dimensional; D008670:Metals; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013525:Surgical Instruments; D013977:Tibia / Q000033:anatomy & histology
D008670:Metals