Inducible displacement CT increases the diagnostic accuracy of aseptic loosening in primary total hip arthroplasty

Background and purpose - Inducible displacement CT compares 2 CTs acquired in series but with alternated rota-tion of the femur. This provides visual and quantitative clues as to the mechanical situation, i.e., loosening, of a total hip arthroplasty. We report the accuracy of this method as well as the experience of integrating it into a clinical workflow. Patients and methods - This was a retrospective single centre study of 72 cases of suspected aseptic loosening were the surgeon after reviewing a standard plain radiograph saw a need for more information. The displacement CT and plain radiograph were compared either to intraoperative findings or a 1-3 year follow up questionnaire for patients that did not have revision surgery. Patients reporting degradation in status since the time of the displacement CT were called for a follow up plain radiograph. Sensitivity and specificity were assessed, and user experience gathered. Results - Of 72 enrolled patients 15 were lost to follow-up. Of the remaining 57, 17 were judged by in-traoperative findings or follow-up to have had loose implants. For plain radiography the sensitivity and specificity were 59% (95% CI 35-82) and 85% (74-96). For displacement CT the cor-responding values were 77% (56-97), and 100% (100-100) respectively. The tool was adaptable to clinical routine. Conclusion - Displacement CT with alternated rota-tions of the femur is a viable option to improve the diag-nostic process for identifying aseptic loosening in a total hip arthroplasty.