Evaluating Length: The Use of Low-dose Biplanar Radiography (EOS) and Tantalum Bead Implantation.

Background: Low-dose biplanar radiography (EOS) is an appealing imaging modality for use in children given its low radiation and ease of use. The goal of this study was to determine the accuracy and reliability of EOS compared with CT scanogram for measurement of leg length and to assess interrater and intrarater reliability of measured interbead distances for EOS and CT scanogram after insertion of tantalum beads into lamb femurs. Methods: Tantalum beads (0.8 mm) were inserted into the cortex on both the medial and lateral sides of 10 skeletally immature lamb femurs. CT scanogram and EOS imaging were obtained. Measurements of total length and distance between bead pairs were recorded on anteroposterior and lateral views by 2 orthopaedic surgeons on 2 separate occasions. Pearson correlations were performed for statistical comparisons. Results: EOS measurements showed near-perfect correlation to those of CT scanogram (r>0.96, P<0.001). Intrarater reliability was excellent for all measurements with EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001) as was interrater reliability for EOS (r>0.98, P<0.001) and CT scanogram (r>0.99, P<0.001). Conclusions: EOS is comparable with CT scanogram in the assessment of limb length and the distance between 2 radiopaque markers. Reliability was excellent for all measurements. The combination of EOS imaging and tantalum bead implantation may be an effective way to evaluate physeal growth following procedures such as epiphysiodesis and physeal bar resection.