Application of weight bearing biplanar stereoradiography in assessment of lower limb deformity

Background: The purpose of this study was to investigate the agreement between the three-dimensional (3D) weight-bearing radiological measurements of leg deformities in the presence of leg rotation and knee flexion in a biplanar stereoradiography system (EOS imaging) and measurements of computed tomography (CT) scans. Methods: Upright biplanar X-rays of six Sawbones; with deformity were registered in no flexion/rotation angle, in 10° and 20° of axial rotation, and 10° and 20° of knee flexion. A CT scan of each bone was registered in supine position, and the 3D reconstruction of each bone was generated. Two-dimensional (2D) lengths and deformity angles were measured on the plain X-rays by two independent observers. Two independent observers generated the 3D reconstructions of the biplanar X-rays and the leg deformity parameters were measured in 3D using custom-developed software. 2D and 3D measurements were compared to CT measurements performed by two observers and repeated three times. The intraclass correlation and limit of agreement between the three measurement techniques were evaluated using Bland-Altman plots. Results: The intraclass correlations were good to excellent for the three imaging modalities (intraclass correlation coefficients = 0.71-0.95). Frontal deformity angles and lengths were significantly different in the 2D X-rays and CT (P 0.05). Conclusions: The 3D measurements of the weight-bearing biplanar X-rays were comparable to 3D CT in assessment of the lower limb deformity.