CT-based migration analysis of a tibial component compared to radiostereometric analysis : one-year results of a prospective single-group implant safety study.

Aims: Radiostereometric analysis (RSA) is considered the gold standard for in vivo migration analysis, but CT-based alternatives show comparable results in the shoulder and hip. We have previously validated a CT-based migration analysis method (CTMA) in a knee phantom compared to RSA. In this study, we validated the method in patients undergoing total knee arthroplasty (TKA). Our primary outcome measure was the difference in maximum total point motion (MTPM) between the differing methods.

Methods: A total of 31 patients were prospectively studied having undergone an uncemented medial pivot knee TKA. Migrations were measured up to 12 months with marker-based and model-based RSA, and CT-RSA.

Results: Mean precision data for MTPM were 0.27 mm (SD 0.09) for marker-based RSA, 0.37 mm (SD 0.26) for model-based RSA, and 0.25 mm (SD 0.11) for CTMA. CTMA was as precise as both RSA methods (p = 0.845 and p = 0.156). At three months, MTPM showed a mean of 0.66 mm (95% CI 0.52 to 0.81) for marker-based RSA, 0.79 (95% CI 0.64 to 0.94) for model-based RSA, and 0.59 (95% CI 0.47 to 0.72) for CTMA. There was no difference between CTMA and marker-based RSA (p = 0.400), but CTMA showed lower migration than model-based RSA (p = 0.019). At 12 months, MTPM was 1.03 (95% CI 0.79 to 1.26) for marker-based RSA, 1.02 (95% CI 0.79 to 1.25) for model-based RSA, and 0.71 (95% CI 0.48 to 0.94) for CTMA. MTPM for CTMA was lower than both RSA methods (p < 0.001). Differences between migration increased between the methods from three to 12 months. Mean effective radiation doses per examination were 0.016 mSv (RSA) and 0.069 mSv (CT). Imaging time for performing RSA radiographs was 17 minutes 26 seconds (SD 7 mins 9 sec) and 4 minutes 24 seconds (SD 2 mins 3 sec) for CT.

Conclusion: No difference in precision was found between CTMA and marker- or model-based RSA, but CTMA shows lower migration values of the tibial component at 12 months. CTMA can be used with low effective radiation doses, and CT image acquisition is faster to perform than RSA methods and may be suitable for use in ordinary clinical settings.