Beschreibung:
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Abstract
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<jats:title>Purpose</jats:title>
<jats:p>Calibration of radiographs is a critical step in digital templating for hip arthroplasty. Calibration errors of > 1.5% lead to over- or undersizing of the templated implants and may affect logistics and patient safety. Contemporary calibration methods are known to be imprecise with average errors of 6.5% and wide variance. A novel bi-planar radiograph-based calibration method is proposed, and a phantom study was conducted as proof of concept.</jats:p>
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<jats:title>Methods</jats:title>
<jats:p>A spherical external calibration marker (ECM) is placed in front of the pubic symphysis of a pelvic bone model at twelve different positions. For each marker position, standard anteroposterior radiographs and four corresponding lateral radiographs with different degrees of rotation (0°–30°) are taken (overall, 60 radiographs). Calibration factors are calculated for an internal calibration marker (ICM) at the centre of the right hip (reference) and the ECM using a novel algorithm. Rotation and marker positions simulate foreseeable use errors and misplacements and aim to test robustness of the method against these errors.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>ECM calibration factor was 125.9% (range 124.7–127.2), and the mean ICM calibration factor was 126.6% (range 126.2–127.1) (<jats:inline-formula><jats:alternatives><jats:tex-math>$$p<0.001$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mo><</mml:mo>
<mml:mn>0.001</mml:mn>
</mml:mrow>
</mml:math></jats:alternatives></jats:inline-formula>). Four images (8.3%) were beyond the 1% error threshold (all with 30° rotation). The mean difference was 0.79% (SD 0.49).</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>The bi-planar method precisely predicts the true calibration factor of the hip joint plane under various conditions. In lateral radiographs, rotation of up to 20° did not adversely affect the precision and all images had calibration errors below the threshold for clinical significance.</jats:p>
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