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Research Papers

Validation of a Feedback-Controlled Elbow Simulator Design: Elbow Muscle Moment Arm Measurement

[+] Author and Article Information
Laurel Kuxhaus

Department of Mechanical and Aeronautical Engineering, Potsdam, NY 13699; Orthopaedic Biomechanics Research Laboratory, Allegheny General Hospital, Pittsburgh, PA 15261

Patrick J. Schimoler

Orthopaedic Biomechanics Research Laboratory, Allegheny General Hospital, Pittsburgh, PA 15212; Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261

Jeffrey S. Vipperman

Department of Mechanical Engineering and Materials Science, and Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261

Mark Carl Miller1

Orthopaedic Biomechanics Research Laboratory, Allegheny General Hospital, Pittsburgh, PA 15261; Department of Mechanical Engineering and Materials Science and Department Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261mcmiller@wpahs.org

1

Corresponding author.

J. Med. Devices 3(3), 031002 (Aug 31, 2009) (7 pages) doi:10.1115/1.3191725 History: Received August 13, 2008; Revised April 06, 2009; Published August 31, 2009

The Allegheny General Hospital (AGH) elbow simulator was designed to be a closed-loop physiologic simulator actuating movement in cadaveric elbow specimens via servoelectric motors that attach to the tendons of the biceps, brachialis, triceps, and pronator teres muscles. A physiologic elbow simulator should recreate the appropriate moment arms throughout the elbow’s range of motion. To validate this design goal, muscle moment arms were measured in three cadaver elbow specimens using the simulator. Flexion-extension moment arms of four muscles were measured at three different pronation/supination angles: fully pronated, fully supinated, and neutral; pronation-supination moment arms were measured at three different flexion-extension angles: 30 deg, 60 deg, and 90 deg. The tendon-displacement method was used in these measurements, in which the ratio of the change in musculotendon length to the change in joint angle was computed. The numeric results compared well with those previously reported; the biceps and pronator teres flexion-extension moment arms varied with pronation-supination position, and vice versa. This is one of the few reports of both flexion-extension and pronation-supination moment arms in the same specimens, and represents the first use of closed-loop feedback control in the AGH elbow simulator. The simulator is now ready for use in clinical studies such as in analyses of radial head replacement and medial ulnar collateral ligament repair.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Drawing and photo of AGH elbow simulator. The inset in the drawing shows a custom pulley assembly.

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Figure 2

Overall schematic of simulator hardware

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Figure 3

Custom potentiometer mounts to measure f/e and p/s

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Figure 4

Flexion/extension moment arms for all specimens

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Figure 5

Pronation/supination moment arms for all specimens

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