A novel calibration method for digital templating of total hip arthroplasty: a prospective clinical study of dual scale
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ORIGINAL PAPER
A novel calibration method for digital templating of total hip arthroplasty: a prospective clinical study of dual scale type single marker calibration in supine radiographs Lennard Loweg 1 & Matthias Trost 2 & Karl Philipp Kutzner 1 & Christian Ries 3 & Christoph Kolja Boese 4 Received: 20 February 2020 / Accepted: 27 April 2020 # SICOT aisbl 2020
Abstract Background External calibration markers (ECM) are the standard of care for digital templating in joint replacements. Spherical mono markers are known to be unreliable. Fixed calibration factors (FCF) can reduce the overall error by placement of markers, but do not address individual patient anatomy. Dual scale calibration marker (DSCM) methods were developed to improve precision of calibration but require two markers. This prospective observational study is the first to analyse the application of a dual scale type single marker (DSSM) method in supine radiographs. Methods One hundred patients with unilateral total hip arthroplasty (THA) underwent anterior-posterior pelvis X-ray with ECM and DSSM. The femoral THA head components were used as internal reference (ICM). An empirical fixed calibration factor (FCF; 120%) was used as comparator. Absolute differences of ICM and both ECM and DSSM were calculated. Absolute relative deviations (ARD) were calculated. Results Mean absolute calibration factor differences of ECM, FCF and DSSM from ICM were 0.105 (0.002–0.182), 0.016 (0.082–0.013) and 0.011 (0.056–0.009), respectively. ARD differences between ECM and DSSM as well as FCF and DSSM were significant (p < 0.001). Conclusion The DSSM method showed superior results over ECM and FCF to predict the optimal calibration factor in supine radiographs. The novel DSSM method could be used to improve digital templating in supine radiographs without need for additional markers. Keywords Digital templating . Total hip arthroplasty . Hip replacement . Calibration . Digital radiograph
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00264-020-04597-8) contains supplementary material, which is available to authorized users. * Christoph Kolja Boese [email protected] 1
Department of Orthopaedic Surgery and Traumatology, St. Josefs Hospital Wiesbaden, Wiesbaden, Germany
2
Department of Orthopaedics and Traumatology, St. Josef-Hospital, Ruhr University Bochum, Bochum, Germany
3
Department of Orthopaedics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
4
Department of Orthopaedic and Trauma Surgery, University Hospital of Cologne, Joseph-Stelzmann-Str. 9, 50924 Cologne, Germany
Total joint replacement of the hip (THA) is a highly standardized procedure. Pre-surgical protocols include anteriorposterior radiograph of the pelvis and digital templating as standard of care [1, 2]. For optimal implant selection, calibration of the radiograph to define the magnification factor of the hip plane is required [1]. The use of one spherical external calibration marker (ECM) at the supposed he
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