Assessment of two-dimensional (2D) and three-dimensional (3D) lower limb measurements in adults: Comparison of micro-dose and low-dose biplanar radiographs

To evaluate reliability of 2D and 3D lower limb measurements in adults using micro-dose compared to low-dose biplanar radiographs(BPR). One hundred patients (mean 54.9 years) were examined twice using micro-dose and low-dose BPR. Length and mechanical axis of lower limbs were measured on the antero-posterior(ap) micro-dose and low-dose images by two independent readers. Femoral and tibial torsions of 50 patients were measured by two independent readers using reconstructed 3D-models based on the micro-dose and low-dose BPR. Intermethod and interreader agreements were calculated using descriptive statistics, intraclass-correlation-coefficient(ICC), and Bland-Altman analysis. Mean interreader-differences on micro-dose were 0.3 cm(range 0-1.0)/ 0.7A degrees(0-2.9) for limb length/axis and 0.4 cm (0-1.0)/0.8A degrees(0-3.3) on low-dose BPR. Mean intermethod-difference was 0.04 cm +/- 0.2/0.04A degrees +/- 0.6 for limb length/axis. Interreader-ICC for limb length/axis was 0.999/0.991 on micro-dose and 0.999/0.987 on low-dose BPR. Interreader-ICC for micro-dose was 0.879/0.826 for femoral/ tibial torsion, for low-dose BPR was 0.924/0.909. Mean interreader-differences on micro-dose/low-dose BPR were 3A degrees(0-13A degrees)/2A degrees(0A degrees-12A degrees) for femoral and 4A degrees(0-18A degrees)/3A degrees(0A degrees-10A degrees) for tibial torsion. Mean intermethod-difference was -0.1A degrees +/- 5.0/-0.4A degrees +/- 2.9 for femoral/tibial torsion. Mean dose-area-product was significantly lower (9.9 times;p < 0.001) for micro-dose BPR. 2D-and 3D-measurements of lower limbs based on micro-dose BPR are reliable and provide a 10-times lower radiation dose. aEuro cent Lower limb length and mechanical axis can be reliably measured with micro-dose. aEuro cent Femoral and tibial torsion can be reliably assessed with micro-dose. aEuro cent Micro-dose allows a huge reduction of radiation exposure.