Background: Measurements of the morphology of the ankle joint, performed mostly\r\nfor surgical planning of total ankle arthroplasty and for collecting data for total ankle\r\nprosthesis design, are often made on planar radiographs, and therefore can be very\r\nsensitive to the positioning of the joint during imaging. The current study aimed to\r\ncompare ankle morphological measurements using CT-generated 2D images with\r\ngold standard values obtained from 3D CT data; to determine the sensitivity of the\r\n2D measurements to mal-positioning of the ankle during imaging; and to quantify\r\nthe repeatability of the 2D measurements under simulated positioning conditions\r\ninvolving random errors.\r\nMethod: Fifty-eight cadaveric ankles fixed in the neutral joint position (standard\r\npose) were CT scanned, and the data were used to simulate lateral and frontal\r\nradiographs under various positioning conditions using digitally reconstructed\r\nradiographs (DRR).\r\nResults and discussion: In the standard pose for imaging, most ankle morphometric\r\nparameters measured using 2D images were highly correlated (R > 0.8) to the gold\r\nstandard values defined by the 3D CT data. For measurements made on the lateral\r\nviews, the only parameters sensitive to rotational pose errors were longitudinal\r\ndistances between the most anterior and the most posterior points of the tibial mortise\r\nand the tibial profile, which have important implications for determining the optimal\r\ncutting level of the bone during arthroplasty. Measurements of the trochlea tali width\r\non the frontal views underestimated the standard values by up to 31.2%, with only a\r\nmoderate reliability, suggesting that pre-surgical evaluations based on the trochlea tali\r\nwidth should be made with caution in order to avoid inappropriate selection of\r\nprosthesis sizes.\r\nConclusions: While highly correlated with 3D morphological measurements, some 2D\r\nmeasurements were affected by the bone poses in space during imaging, which may\r\naffect surgical decision-making in total ankle arthroplasty, including the amount of bone\r\nresection and the selection of the implant sizes. The linear regression equations for the\r\nrelationship between 2D and 3D measurements will be helpful for correcting the errors\r\nin 2D morphometric measurements for clinical applications.
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