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2015 Abstracts

Hip Joint Center Differences between Dual Fluoroscopy, Functional Hip and Coda—Establishing a Reference Standard

Michael Kutschke and Niccolo Fiorentino

University of Utah

Measurements of joint angles, moments, and forces can be sensitive to positional changes in the center of a joint. Due to its deep location, the hip joint center (HJC) can be difficult to determine. Regression equations and functional methods use skin markers and are commonly used to measure the HJC, yet introduce sources of error such as bony landmark identification, soft tissue artifact, and system resolution. Additionally, the accuracy of said methods cannot be established in-vivo without a reference standard. The purpose of this study was to implement a dual fluoroscopy (DF) and model-based tracking technique to quantify the subject-specific HJC position in-vivo. This reference standard (DF-HJC) was then compared to the HJC defined by regression equations (CODA) and a functional method (FHJC) using skin markers. Five subjects with normal hip anatomy provided informed consent to participate in this IRB approved study. A gait marker set was applied to the subject’s skin. The subject performed various activities involving the inferior limb while a 10-camera Vicon system measured the position of the skin markers. From these data, the CODA and FHJCs were identified. Simultaneously, the hip was visualized using a DF system, and the DF-HJC was identified using model-based tracking. The DF-HJC was then transformed to the Vicon coordinate system for comparison with the CODA and FHJCs. The average Euclidean distance (and standard deviation) for the five subjects from the DF-HJC was 2.0 (0.6) cm for CODA and 1.3 (0.4) cm for the FHJC. To our knowledge this is the first study to use DF and model-based tracking to measure the in-vivo position of the HJC. This technique affords greater accuracy in determining subject-specific bone geometry and visualization of deep hip anatomy, thus may be considered a reference standard for identifying the HJC.