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TECHNICAL PAPERS: Joint/Whole Body

Validation of a New Model-Based Tracking Technique for Measuring Three-Dimensional, In Vivo Glenohumeral Joint Kinematics

[+] Author and Article Information
Michael J. Bey

 Henry Ford Health Systems, Department of Orthopaedics and Rehabilitation, Bone and Joint Center, E&R 2015, 2799 W. Grand Blvd., Detroit, MI 48202bey@bjc.hfh.edu

Roger Zauel, Stephanie K. Brock, Scott Tashman

 Henry Ford Health Systems, Department of Orthopaedics and Rehabilitation, Bone and Joint Center, E&R 2015, 2799 W. Grand Blvd., Detroit, MI 48202

J Biomech Eng 128(4), 604-609 (Jan 31, 2006) (6 pages) doi:10.1115/1.2206199 History: Received July 07, 2005; Revised January 31, 2006

Shoulder motion is complex and significant research efforts have focused on measuring glenohumeral joint motion. Unfortunately, conventional motion measurement techniques are unable to measure glenohumeral joint kinematics during dynamic shoulder motion to clinically significant levels of accuracy. The purpose of this study was to validate the accuracy of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics. We have developed a model-based tracking technique for accurately measuring in vivo joint motion from biplane radiographic images that tracks the position of bones based on their three-dimensional shape and texture. To validate this technique, we implanted tantalum beads into the humerus and scapula of both shoulders from three cadaver specimens and then recorded biplane radiographic images of the shoulder while manually moving each specimen’s arm. The position of the humerus and scapula were measured using the model-based tracking system and with a previously validated dynamic radiostereometric analysis (RSA) technique. Accuracy was reported in terms of measurement bias, measurement precision, and overall dynamic accuracy by comparing the model-based tracking results to the dynamic RSA results. The model-based tracking technique produced results that were in excellent agreement with the RSA technique. Measurement bias ranged from 0.126to0.199mm for the scapula and ranged from 0.022to0.079mm for the humerus. Dynamic measurement precision was better than 0.130mm for the scapula and 0.095mm for the humerus. Overall dynamic accuracy indicated that rms errors in any one direction were less than 0.385mm for the scapula and less than 0.374mm for the humerus. These errors correspond to rotational inaccuracies of approximately 0.25deg for the scapula and 0.47deg for the humerus. This new model-based tracking approach represents a non-invasive technique for accurately measuring dynamic glenohumeral joint motion under in vivo conditions. The model-based technique achieves accuracy levels that far surpass all previously reported non-invasive techniques for measuring in vivo glenohumeral joint motion. This technique is supported by a rigorous validation study that provides a realistic simulation of in vivo conditions and we fully expect to achieve these levels of accuracy with in vivo human testing. Future research will use this technique to analyze shoulder motion under a variety of testing conditions and to investigate the effects of conservative and surgical treatment of rotator cuff tears on dynamic joint stability.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 3

Single-frame model-based tracking solution for the scapula (left) and humerus (right). In each image, the two digitally reconstructed radiographs (DRRs)—i.e., the highlighted bones in each image—are superimposed over the original pair of biplane x-ray images in the position and orientation that maximized the correlation between the DRRs and biplane x-ray images. Note that the implanted tantalum beads, which are visible in the fluoroscopic images, have been removed from the volumetric CT bone model and thus do not appear in the DRRs.

Grahic Jump Location
Figure 1

Flow chart showing the process used by the model-based tracking algorithm to find a bone’s optimal position and orientation from a pair of biplane x-ray images

Grahic Jump Location
Figure 2

A pair of digitally reconstructed radiographs (DRRs) are constructed from the CT bone model. The position and orientation of the CT bone model is refined to optimize the correlation between the two DRRs and the two biplane x-ray images.

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