This article has been retracted. See "Retraction: Comparison of Accuracy of Navigation between Infrared Optical and Electromagnetic Systems" in Volume 49 on page 496.
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 (10.25°±5.10°) than Orthopilot (9.02°±5.18°). The mean mechanical axis difference was 1.23° and a difference greater than 3° in the same patient occurred in 15% of patients. For the synthetic bone, the true mechanical axis was varus 1.25°, OrthoPilot displayed varus 1.10°±0.64° and AxiEM varus 1.78°±0.79°. 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 3° in 15% between the two navigation methods in the same patient.
Figures and Tables
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.
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.
Fig. 3
(A-C) Erroneous identification of anatomical landmarks: (A) Distal femur, (B) Proximal tibia, and (C) Ankle.
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.
Table 1
Preoperative Mechanical Axis of TKA Patients Preoperatively Determined Using Both Navigation Systems
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