Precision of computer tomography based RSA on femoral implants in total knee arthroplasty: A porcine cadaver study

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BACKGROUND: Radiostereometric analysis is the gold standard for assessing migration of orthopaedic implants. The novel CT-based radiostereometric analysis yields high precision of evaluation of tibial implants. We analyzed the precision of CT-based radiostereometric analysis on femoral implants in knee arthroplasty at different dose levels, and compared it to previously published results on tibial implants and the available literature on precision of radiostereometric analysis. METHODS: We performed a total knee arthroplasty on a porcine cadaver knee. In the subsequent 7 CT scans, we analyzed the precision of the CT-based radiostereometric analysis method in 21 samples at two different effective doses (standard and low dose), and compared this to literature on radiostereometric analysis. FINDINGS: CT-based radiostereometric analysis of maximum total point motion of femoral and tibial components showed a precision difference of (mean, 95 % confidence interval) 0.18 mm (0.13 to 0.22), P < 0.001. For femoral implants (mean, 95 % confidence interval, standard deviation) we found precisions of 0.25 mm (0.21-0.29, 0.1) and 0.29 (0.25-0.32, 0.08) mm for the standard and low dose protocols respectively. Variability ratios of tibia versus femur and standard versus low dose femur (95 % confidence interval) were 18.3 (7.4-45.1) and 0.7 (0.3-1.7) with respective P-values of <0.001 and 0.40. INTERPRETATION: CT-based radiostereometric analysis on femoral implants in total knee arthroplasty is feasible and has a lower, yet still acceptable, precision compared to CT-based radiostereometric analysis on tibial implants in a porcine cadaver. However, confirmation in clinical studies is warranted.

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