Comparison of radiographic vs. computed tomography canal filling ratio measurement of stems in revision knee prostheses.

Background: Lack of consensus on which measurement method gives the most accurate results for medullary canal filling ratio (CFR) of stems used in revision knee prostheses causes confusion when interpreting scientific studies. Therefore, the present study aims to find the most accurate measurement method of CFR on direct radiographs. Methods: Twenty-eight femoral and 27 tibial components of 29 patients with a mean age of 72.86 ± 6.32 years were included in the study. Two different methods were used for computerized tomography CFR measurement. These methods and five different radiographic measurement methods used for CFR were compared statistically. Results: There was no statistically significant difference between the real tomographic CFR of the femoral stem and the CFR calculation made by using ellipse area (p > 0.05). There was also no statistically significant difference between the tomographic CFR measurement calculated according to the largest stem size that can be implanted, and the method that accepted the smallest value as CFR after the measurement made according to Parsley's method on AP and lateral radiographs (p > 0.05). The results obtained by using all other tests were statistically different from each other. Conclusion: CFR calculation made by using ellipse area, is the most accurate method for femoral stem CFR. The method that accepted the smallest value as CFR after the measurement made according to Parsley's method on AP and lateral radiographs is the most accurate method for tibial stem CFR.