Computed tomography-based radiostereometric analysis achieves sufficient precision for femoral implants in total knee arthroplasty: a randomized controlled trial

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BACKGROUND: Conventional radiostereometric analysis (RSA) has been used for several decades to assess implant migration in total knee arthroplasty (TKA). More recently, computed tomography-based radiostereometric analysis (CT-RSA) has been introduced as an alternative. Experimental studies have demonstrated acceptable precision for CT-RSA; however, this has not yet been validated in a clinical setting. With the emergence of new alignment philosophies in TKA, migration analysis of femoral components has become increasingly important. A key criticism of CT-RSA has been the higher radiation doses compared with conventional RSA, particularly in longitudinal studies involving repeated CT scans. In this study, we evaluated the precision of CT-RSA for assessing femoral component migration in two TKA designs at two different radiation dose levels. We hypothesized that there would be no clinically relevant difference in precision between the two radiation dose levels. METHODS: We performed a randomized controlled trial of 50 patients using Tritanium and GMK Sphere 3D Metal implants and analysed the precision of the method through double examinations expressed as means with 95% confidence intervals at standard and low-dose levels. The main outcome variable was the difference in mean maximum total point motion. We set the clinical meaningful difference to be more than 0.1 mm based on existing literature. Secondary outcome variables were the means and standard deviations of the translation and rotation of the implants. FINDINGS: We found a precision of (mean, standard deviation) 0.20 (0.08) and 0.17 mm (0.06) for standard and low dose respectively, giving a difference (95% confidence interval) of - 0.03 mm (- 0.06-0.00). P-value was 0.031. Variability ratios were 0.009 for the standard deviation test. INTERPRETATION: In this first clinical study to assess the precision of computed tomography-based radiostereometric analysis for femoral implants in total knee arthroplasty, we found no clinically relevant difference in precision. Our findings confirm that CT-RSA provides sufficient precision in a clinical setting to enable migration analysis of femoral implants in total knee arthroplasty, even when using very low radiation doses.

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