CT-Based Radiostereometric Analysis: A Promising Alternative to Conventional Radiostereometric Analysis in Determining Polyethylene Wear in Total Hip Arthroplasty.

Background: CT-based radiostereometric analysis (CT-RSA) enables the measurement of early implant migration after Total Hip Arthroplasty (THA) with high precision and accuracy at a low effective radiation dose. This study is the first to investigate whether CT-RSA might be comparable to conventional radiostereometric analysis(RSA) even for in vivo polyethylene liner wear measurements after THA. Purpose: To evaluate the comparability of CT-based RSA and conventional RSA for measuring polyethylene liner wear after THA. Materials and Methods: A total of 8 patients treated with a reverse hybrid THA (cemented cup and uncemented stem) were included from an ongoing RSA study. CT-RSA and RSA images were taken immediately postoperatively and after 6 years to compare measurements of the polyethylene wear. Double examinations were performed to estimate the precision of the CT-RSA method. Results: Wear measured as median proximal translation of the femoral head into the cup at 6 years was 0.10 mm (IQR 0.02-0.17 mm) as measured by RSA and 0.13 mm (IQR 0.04-0.27 mm) by CT-RSA. Bland-Altman plots indicated good agreement between the methods; for proximal wear the mean difference between methods was 0.04 mm (limits of agreement -0.37-0.46 mm). Proximal wear precision was 0.16 mm for RSA and 0.15 mm for CT-RSA. The mean effective radiation dose was 0.2 mSv per CT scan and 0.04 mSv per RSA scan. Conclusion: This exploratory study suggests that CT-RSA provides wear measurements comparable to those obtained with conventional RSA and may therefore represent a viable alternative for evaluating liner wear in future implant studies.