Reliability and Reproducibility of Subject Positioning with EOS Low-Dose Biplanar X-ray.

BACKGROUND: EOS low-dose biplanar X-ray used with tantalum bead implantation is an appealing imaging modality to evaluate limb length and physeal growth due its relatively low radiation exposure, excellent inter- and intra-observer reliability, and minimal magnification/shrinkage error.

QUESTIONS/PURPOSES: The purpose of this study was to establish the error in total length and inter-bead distances using EOS and tantalum beads due to variable positioning in the EOS gantry, by assessing variation in measurements made on the same subject repeatedly positioning by one positioner (intra-positioner measurement error) and variation in measurements made on the same subject with positioning by multiple positioners (inter-positioner measurement error).

METHODS: Tantalum bead markers were placed about the distal femoral physis of a cadaveric lamb femur. Three investigators positioned the femur in the EOS gantry 10 times, totaling 30 EOS scans. Total limb length and inter-bead distances were measured on AP and lateral views; mean and standard error were calculated. A random effects analysis of variance for nested data was used to determine the proportion of variation due to differences between positioners and differences between positioning by the same positioner.

RESULTS: Intra-positioner measurement error ranged from 0.01 to 0.06 mm. Inter-positioner measurement error ranged from 0.00 to 0.09 mm.

CONCLUSIONS: EOS has relatively low radiation and allows standing assessment of limb length and alignment. In this study, length measurements and inter-bead distances demonstrated minimal error due to positioning in the EOS gantry, documenting that there is minimal error from positioning, minimal magnification/shrinkage error, and exceptional inter and intra-rater reliability. EOS is the preferred method for length and angular measurements, and with tantalum beads, is ideal for measuring growth about the physis.