Validation and reproducibility of a biplanar imaging system versus conventional radiography of foot and ankle radiographic parameters.

BACKGROUND

Diagnosis of foot deformities is frequently supported by objective measures of bony alignment made on AP and lateral weight-bearing radiographs. The EOS biplanar imaging system has the capability of simultaneously capturing orthogonal AP and lateral images of the foot during weight-bearing with reduced radiation exposure. The purpose of this study was to evaluate the validity and reproducibility of common foot and ankle radiographic measurements made on images acquired with the EOS biplanar imaging system.

METHODS

Fifty consecutive patients indicated for foot and ankle realignment surgeries were enrolled. Radiographic studies included conventional AP and lateral ankle weight-bearing radiographs and long-leg AP and lateral weight-bearing images acquired using the EOS system with both a staggered feet and a nonstaggered feet position. Sixteen radiographic parameters of foot, ankle, and lower limb alignment were measured by 2 blinded observers, with 1 observer repeating all measurements 6 weeks later. Inter- and intraobserver reliability was assessed using intraclass correlation coefficients. Between-group comparison was assessed using Pearson correlation coefficients, ANOVA, and paired t-tests.

RESULTS

There was no statistically significant difference in any commonly used foot and ankle radiographic parameters measured on conventional radiographs or EOS images acquired with staggered and nonstaggered feet (ANOVA P = .792 to .997 and paired t tests P = .067 to .977). However, the staggered foot position resulted in significantly different limb length measurements in the rear leg (P = .000 to .049). Intra- and interrater reliabilities of limb alignment measurements from EOS system images were excellent in both foot positions (ICC = .938 to 1.000).

CONCLUSION

Images acquired using EOS biplanar imaging system allowed for valid and reliable measurement of commonly used foot and ankle radiographic parameters; however, the staggered foot position required for simultaneous imaging of both feet in the lateral view affected limb length measurements in the rear leg.

LEVEL OF EVIDENCE: Level II, prospective comparative study.