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 rotation 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 corresponding values were 77% (56–97), and 100% (100–100) respectively. The tool was adaptable to clinical routine. CONCLUSION: Displacement CT with alternated rotations of the femur is a viable option to improve the diagnostic process for identifying aseptic loosening in a total hip arthroplasty.