Abstract
BackgroundWhole body standing alignment (WBSA) in terms of biomechanics can be evaluated accurately only by referring the gravity line (GL) which lies on the gravity center (GC). Here, we introduce a method for estimating GL and simultaneous WBSA measurement using the EOS® imaging system and report on the reproducibility and reliability of the method.MethodsA 3-dimensional (3D) avatar to estimate GC was created following three steps: 3D reconstruction of the bone based on EOS images; deformation into a generic morphotype (MakeHuman statistical model) before density integration with 3D rasterization of the full body into 1-mm3 voxels (the content of each voxel is considered homogeneous); computation of the density of all the voxels provides the center of mass, which can be projected onto the floor as the GC of the full body, providing the GL in relation to the WBSA. The repeatability, reproducibility, and accuracy of the estimated GC and body weight of the avatar were compared with clinical estimation using a force plate in healthy volunteers and patients with degenerative and deformative diseases.ResultsStatistical analyses of the data revealed that the repeatability and reproducibility of the estimation was high with intra-rater and inter-rater intraclass correlation coefficient. ≥0.999. The coordinate values of the GC and body weight estimation did not differ significantly between the avatar and force plate measurements, demonstrating the high accuracy of the method.ConclusionThis new method of estimating GC and WBSA is reliable and accurate. Application of this method could allow clinicians to quickly and qualitatively evaluate WBSA with GL with various spinal malalignment pathologies.
Highlights
Whole body standing alignment (WBSA) in terms of biomechanics can be evaluated accurately only by referring the gravity line (GL) which lies on the gravity center (GC)
The objective of this study is to introduce the gravity center (GC) estimation for determining the GL using EOS-based virtual barycentremetry; to verify its repeatability, reproducibility, and accuracy when compared to estimation by force plate and report preliminary clinical results
Radiologic measurement by the EOS system There was significant difference in T1 pelvic angle (TPA), lumbar lordosis (LL), pelvic incidence (PI)-LL, SS, pelvic tilt (PT), and Knee flexion among the groups, with greater values in TPA, PI-LL, PT, and Knee flexion, and with lesser values in LL and SS, in Degenerative and Deformative compared with Normal group
Summary
Whole body standing alignment (WBSA) in terms of biomechanics can be evaluated accurately only by referring the gravity line (GL) which lies on the gravity center (GC). The resulting sagittal malalignment is compensated by all the parts of the axial skeleton, especially by increases in cervical lordosis, pelvic tilt, and knee flexion in accordance with the grade of malalignment, to maintain a standing posture with a horizontal gaze [2,3,4,5,6,7,8,9,10] The greater the malalignment, the more muscle activity is required to maintain a standing posture, leading to fatigue and pain in the back and lower limbs and subsequent deterioration of health-related quality of life. A recent advance in radiologic devices was realized to show the WBSA using biplanar slot-scanning stereoradiography (EOS®, EOS Imaging, Paris, France), which is becoming the gold standard for evaluating standing alignment [16]
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