Abstract
Digital templating with external calibration markers is the standard method for planning total hip arthroplasty. We determined the geometrical basis of the magnification effect, compared magnification with external and internal calibration markers, and examined the influence on magnification of the position of the calibration markers, patient weight, and body mass index (BMI). A formula was derived to calculate magnification with internal and external calibration markers, informed by 100 digital radiographs of the pelvis. Intraclass correlations between the measured and calculated values and the strength of relationships between magnification, position and distance of calibration markers and height, weight, and BMI were sought. There was a weak correlation between magnification of internal and external calibration markers (r = 0.297–0.361; p < 0.01). Intraclass correlations were 0.882–1.000 (p = 0.000) for all parameters. There were also weak correlations between magnification of internal and external calibration markers and weight and BMI (r = 0.420, p = 0.000; r = 0.428, p = 0.000, respectively). The correlation between external and internal calibration markers was poor, indicating the need for more accurate calibration methods. While weight and BMI weakly correlated with the magnification of markers, future studies should examine this phenomenon in more detail.
Highlights
Digital templating has become the standard method of preoperative planning for total hip arthroplasty, aiming to optimize component choice and positioning, and to minimize the risk of intra- and postoperative complications [1]
We identified 100 standing anteroposterior (AP) radiographs of the pelvis from the hospital picture archiving and communication system (PACS) in a retrospective search that spanned March 2012 to September 2014
Preoperative templating is the accepted standard for planning total hip arthroplasty, and digital techniques have almost completely superseded the use of acetate templating [1]
Summary
Digital templating has become the standard method of preoperative planning for total hip arthroplasty, aiming to optimize component choice and positioning, and to minimize the risk of intra- and postoperative complications [1]. Calibration requires standardized radiographs of the pelvis to be compared with an object of known size, while conventional acetate templating relies on a fixed magnification [2]. The external calibration marker (ECM), usually a sphere, should be positioned at the height of the region of interest (ROI; i.e., the center of the hip joint) relative to the detector plate and central beam [1,2]. Calibration Markers for Digital Templating specific factors [3]. Patients may find the requirement to position the ECM near the anus and genitals distressing or uncomfortable[4]
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