Evaluation of conventional and CT-based radiostereometric analysis for inducible displacement measurements after total hip arthroplasty

Though radiostereometric analysis (RSA) is the gold standard for migration tracking, computed tomography-based RSA (CT-RSA) does not require marker beads and is available for clinical adoption. This study investigated CT-RSA in comparison to RSA for assessing hip implant stability with inducible displacement (ID) examinations. Patients (n = 48) from a previous study returned to be re-examined for femoral stem stability with CT-RSA and RSA imaging. Implant migration since patients last follow-up was calculated as a measure of stability. ID was assessed between alternated leg rotation scans for CT-RSA and between supine and weight-bearing scans for RSA. Measurements from ID and double examinations were compared between CT-RSA and RSA. All stems were well-fixed with migration <0.2 mm/year. ID measurements were lower with CT-RSA than RSA for distal translation (mean difference = 0.122 mm, p < 0.0001), total translation (mean difference = 0.158 mm, p < 0.0001), and total rotation (mean difference = 0.449°, p < 0.0001). The ID and double exam were significantly different for total translation and total rotation for CT-RSA, and significantly different for medial, distal, and total translation, and total rotation for RSA. Precision ranged from 0.049 to 0.130 mm in translation and 0.061° to 0.220° in rotation for CT-RSA, and from 0.108 to 0.269 mm in translation and 0.151° to 0.670° in rotation for RSA. ID measurements from both CT-RSA and RSA were minimal, consistent for a cohort with well-fixed stems. CT-RSA demonstrated superior precision in all axes compared to RSA. Clinical Significance: Future work should explore the use of CT-RSA in patients with suspected loosening as a potential diagnostic tool.