J Korean Orthop Assoc.  2009 Feb;44(1):68-75. 10.4055/jkoa.2009.44.1.68.

Comparison of Accuracy of Navigation between Infrared Optical and Electromagnetic Systems

• Song EK
• Seon JK
• Park SJ
• Yoon TR
• Park KS
• Kim SK

• KMID: 2186380
• DOI: http://doi.org/10.4055/jkoa.2009.44.1.68

Abstract

PURPOSE: This study compared the accuracy of mechanical axis measurement between infrared optical and electromagnetic navigation.
MATERIALS AND METHODS
We compared the preoperative mechanical axes of 20 TKAs using both navigation systems. Experimentally, the mechanical axes of the synthetic bone model were compared and the true mechanical axis was determined using the ORTHODOC. Additionally, a surgeon intentionally registered incorrect landmarks and then measured the amount of mechanical axis change in the two navigation methods.
RESULTS
Clinically, AxiEM provided greater varus (10.25degrees+/-5.10degrees) than Orthopilot (9.02degrees+/-5.18degrees). The mean mechanical axis difference was 1.23degrees and a difference greater than 3degrees in the same patient occurred in 15% of patients. For the synthetic bone, the true mechanical axis was varus 1.25degrees, OrthoPilot displayed varus 1.10degrees+/-0.64degrees and AxiEM varus 1.78degrees+/-0.79degrees. The mechanical axis differences were not significantly different, but OrthoPilot had more reproducibility. When anatomical landmarks were erroneously identified, AxiEM showed a greater change in the mechanical axis.
CONCLUSION
Both navigation systems provided high mechanical axis accuracy and reproducibility under experimental conditions. Infrared optical navigation was more reproducible than electromagnetic navigation. In the clinical setting, there was a disparity of mechanical axis difference greater than 3degrees in 15% between the two navigation methods in the same patient.

Keyword

Infrared optical navigation; Electromagnetic navigation; Accuracy; Total knee arthroplasty

MeSH Terms

Axis, Cervical Vertebra
Humans
Intention
Magnets

Figure

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  Fig. 1 Synthetic bone models. The hip, knee and ankle joint are made of titanium which have no effect on electromagnetic field and the knee joint is constrained not allowing varus or valgus motion.

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  Fig. 2 (A-E) Proceeding of ORTHODOC system: (A) Femoral head center, (B) Center of distal femur, (C) Center of proximal tibia, (D) Ankle center, and (E) Measurement of mechanical axis.

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  Fig. 3 (A-C) Erroneous identification of anatomical landmarks: (A) Distal femur, (B) Proximal tibia, and (C) Ankle.

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  Fig. 4 Results of mechanical axis evaluation using Orthopilot and AxiEM navigation system. Orthopilot read mechanical axis as 0, 1, 2° varus and AxiEM did 0 to 3° varus. Orthopilot showed more reproducibility. Both navigations demonstrated 1 or 2° varus in 86%. But, this study revealed two systems could make 3° of mechanical axis difference in the worst scenario. MA, mechanical axis; EM, Electromagnetic navigation; -, negative symbol indicates varus.

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