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Pelvic Rotation and Inclination Affect Reliability of Sagittal Pelvic Alignment and Anterior Pelvic Plane Angle Measured by EOS System

4 pagesPublished: August 17, 2017


The Difficulties to obtain acceptable pelvic reference points on bi- planar X-ray images for EOS measurements change as the patient’s pelvis rotated or inclined. The aim of this study was to clarify the effects of pelvic Z-axis rotation (rotation) and X-axis rotation (inclination) on the measurement values of SS, PT, and APP angle by using of EOS. Methods: We obtained anteroposterior and lateral X-ray images of a trunk phantom which was rotated and inclined in standing position by using of the EOS. Sacral slope (SS) and pelvic tilt (PT) as parameters to judge patient’s pelvic alignments by spinal surgeons, and anterior pelvic (APP) angle as a reference to decide patient’s pelvic alignments by hip surgeons were measured with the EOS software. The values of SS and PT and APP angle were compared in the phantom rotation and inclination. Results: PT showed small changes when the phantom was rotated, however, SS decreased and APP angle increased when the phantom was rotated. The values of SS and PT dispersed at 300 rotation among each inclination. APP angle dispersed at -15o and 30o of rotation among each inclination. Conclusion: Measurement variations of SS and PT were small amount under 15 degrees of rotation and inclination. On the contrary, APP angles showed greater variations when the phantom was rotated and inclined. Proper positioning of subjects, by reducing rotational effects, is important to get constant reproducible measurements, even if we use EOS system.

Keyphrases: Anterior pelvic plane angle, app, EOS imaging, Standing Sagittal pelvic alignment

In: Klaus Radermacher and Ferdinando Rodriguez Y Baena (editors). CAOS 2017. 17th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery, vol 1, pages 359--362

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