Introduction. Cup position is critical to stability in total hip arthroplasty and is affected by pelvis motion during positions of daily\nlife.The purpose of this study was to explicitly define the relationship between sagittal pelvic motion and resultant cup functional\nanteversion and create a tool to guide the surgeon to a patient-specific intra-operative anteversion. Materials and Methods. 10,560\ncombinations of inclination, anteversion, and pelvic tilt were generated using a geometric model. Resultant functional anteversion\nwas calculated for each iteration and variableswere correlated.Anelectronicmobile toolwas created that compares inputted patientspecific\nvalues to population-based averages to determine pelvic positions and dynamics that may lead to instability. Results. A\nthird-degree polynomial equationwas used to describe the relationship between variables.Thefreely downloadablemobile tool uses\ninput from pre-operative plain radiographic measurements to provide the surgeon a quantitative correction to intra-operative cup\nanteversion based on differences in functional anteversion compared to population-based averages. Conclusion.This study provides\na geometric relationship between planned cup position, pelvic position and motion, and the resultant functional anteversion. This\nmathematical model was applied to an electronic tool that seeks to determine an individualized intra-operative cup anteversion\nbased on measured patient-specific pelvic dynamics.
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