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Degen, Nikolaus; Suero, Eduardo; Bogusch, Miriam; Neuerburg, Carl; Manz, Kirsi Marjaana ORCID: 0000-0002-7740-4076; Becker, Christopher A.; Befrui, Nima; Kammerlander, Christian; Böcker, Wolfgang; Zeckey, Christian (2020): Intraoperative use of cortical step sign and diameter difference sign: Accuracy, inter-rater agreement and influence of surgical experience in subtrochanteric transverse fractures. In: Orthopaedics & traumatology, surgery & research: OTSR [Forthcoming]
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BACKGROUND The cortical step sign (CSS) and diameter difference sign (DDS) are radiographic tools for torsional alignment control in intramedullary nailing. They have been found to be highly relevant in objective radiographic measurements, but for intraoperative visual identification they lack sufficient evidence yet. The aim of this experimental study was to evaluate their (1) accuracy, (2) inter-rater agreement, (3) predictors of correct identification for clinically relevant maltorsion (CRM: \geq15°), and (4) positive and negative predictive values. HYPOTHESIS Sensitivity and specificity of CSS and DDS in visual identification of CRM are comparable to those in objective measurement. MATERIAL AND METHODS Six observers of three different levels of surgical experience evaluated 50 a.p. and 50 lateral views of subtrochanteric fractures of cadaveric specimens with internal/external maltorsion from 0° to 30° to assess for CSS, DDS, and CRM. (1) Sensitivity and specificity were evaluated. Percentage agreement and Cohen's Kappa were used to evaluate accuracy as agreement with measured/true values and (2) inter-rater agreement. To determine (3) significant predictors of correct identification of the CSS, DDS, and CRM, a mixed-effects logistic model was constructed, and (4) predictive values were calculated. RESULTS (1) Sensitivities of CSS and DDS for CRM (0.99±0.03 and 0.88±0.06) were close to those in objective measurement (1.00 and 0.90). So were specificities (0.25±0.08 and 0.47±0.17 vs. 0.32 and 0.47). Agreement percentage for CSS was high (90-94%, kappa 0.40-0.69), for DDS and CRM it was slightly lower (74-82%, kappa 0.34-0.57 and 62-76%, kappa 0.26-0.49). (2) Inter-rater agreement also showed the highest values for CSS (88-96%, kappa 0.51-0.73) with slightly lower values for DDS (74-84%, kappa 0.36-0.63) and CRM (62-84%, kappa 0.21-0.68). (3) Training level and the magnitude of maltorsion were found the most relevant predictors of a correct identification of CSS/DDS/CRM. (4) DDS showed a higher positive predictive value (73.1%), CSS a higher negative predictive value (93.5%). DISCUSSION We found visual identification of CSS and DDS to be almost as accurate as objective measurement in the detection of CRM. Estimation of maltorsion is not sufficiently reliable, but a negative CSS excludes a CRM with high probability. Both signs should be applied by experienced surgeons. LEVEL OF EVIDENCE Level III, experimental setting, non-randomised experimental trial.