Introduction: Accurate measurement of cup version on plain radiographs remains difficult due to the two-dimensional projection of an ellipse and difficulty obtaining reproducible radiographs. Purpose: Determine: 1) if the cup angle measured on the false profile view (FPV) could be used to determine radiographic cup version; 2) how patient positioning would affect cup angle measurement on the FPV; 3) if implant cup design affects cup angle measurement. Materials and methods: Three cup version positions were assessed in a sawbone: 13° (normal); 28° (excessive anteversion) and -2° (retroversion). Cup angle was measured on the FPV at five different degrees of pelvic rotation within each cup version group. Pelvic rotation was quantified using the ratio of the inter-femoral head distance measured on the FPV versus the anteroposterior radiographs (FP/AP ratio). Eighty patients (40 metal-on-polyethylene, 40 metal-on-metal) post-total hip were also assessed. Cup version was assessed with Einzel-Bild-Roentgen-Analysis software (EBRA). R<sup>2</sup> was calculated to assess correlation between both measurement methods. Results: For the sawbone model, an R<sup>2</sup> of 0.95 was obtained. For patients, overall R<sup>2</sup> was 0.56 with an FP/AP ratio of 0.3-0.49 having an R<sup>2</sup> of 0.72. The EBRA anteversion versus cup angle scatterplot had an R<sup>2</sup> of 0.72 (95%CI: +/-7.8°). Subgroup analysis revealed no differences between the metalon-poly and metal-on-metal for cup angle measurements. The intra-class coefficient for intra and inter-observer reliability for all cases (individual and combined FP/AP groups) was 0.98 to 0.99. Conclusion: The FPV cup angle measurement value provides an accurate measurement of radiographic cup anteversion with well-defined patient position parameters.

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Keywords Acetabular version, False-profile view, Total hip replacement
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Journal HIP International
Lee, J.K.L. (Joshua K. L.), Sardana, V. (Vandit), White, C. (Craig), Speirs, A, & Beaulé, P.E. (Paul E.). (2014). Cup version can be accurately measured on the false profile view radiograph. HIP International, 24(4), 347–354. doi:10.5301/hipint.5000151