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Technical Briefs

Rectus Femoris Knee Muscle Moment Arms Measured in Vivo During Dynamic Motion With Real-Time Magnetic Resonance Imaging

[+] Author and Article Information
Niccolo M. Fiorentino

Department of Mechanical & Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22908;
Laboratory of Cardiac Energetics,
Division of Intramural Research,
National Heart, Lung, and Blood Institute,
National Institutes of Health, DHHS,
Bethesda, MD 20892

Jonathan S. Lin, Michael A. Guttman

Laboratory of Cardiac Energetics,
Division of Intramural Research,
National Heart, Lung, and Blood Institute,
National Institutes of Health, DHHS,
Bethesda, MD 20892

Kathryn B. Ridder

Department of Mechanical & Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22908

Elliot R. McVeigh

Laboratory of Cardiac Energetics,
Division of Intramural Research,
National Heart, Lung, and Blood Institute,
National Institutes of Health, DHHS,
Bethesda, MD;
Department of Biomedical Engineering,
Johns Hopkins University School of Medicine,
Baltimore, MD 21205

Silvia S. Blemker

Department of Mechanical & Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22908;
Department of Biomedical Engineering,
University of Virginia,
Charlottesville, VA 22908
e-mail: ssblemker@virginia.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received September 23, 2012; final manuscript received January 11, 2013; accepted manuscript posted January 29, 2013; published online April 2, 2013. Assoc. Editor: Tammy Haut Donahue.

J Biomech Eng 135(4), 044501 (Apr 02, 2013) (5 pages) Paper No: BIO-12-1429; doi: 10.1115/1.4023523 History: Received September 23, 2012; Revised January 11, 2013; Accepted January 29, 2013

Moment arms represent a muscle's ability to generate a moment about a joint for a given muscle force. The goal of this study was to develop a method to measure muscle moment arms in vivo over a large range of motion using real-time magnetic resonance (MR) imaging. Rectus femoris muscle-tendon lengths and knee joint angles of healthy subjects (N = 4) were measured during dynamic knee joint flexion and extension in a large-bore magnetic resonance imaging (MRI) scanner. Muscle-tendon moment arms were determined at the knee using the tendon-excursion method by differentiating measured muscle-tendon length with respect to joint angle. Rectus femoris moment arms were averaged across a group of healthy subjects and were found to vary similarly during knee joint flexion (mean: 3.0 (SD 0.5) cm, maximum: 3.5 cm) and extension (mean: 2.8 (SD 0.4) cm, maximum: 3.6 cm). These moment arms compare favorably with previously published dynamic tendon-excursion measurements in cadaveric specimens but were relatively smaller than moment arms from center-of-rotation studies. The method presented here provides a new approach to measure muscle-tendon moment arms in vivo and has the potential to be a powerful resource for characterizing musculoskeletal geometry during dynamic joint motion.

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Figures

Grahic Jump Location
Fig. 1

Experimental setup. The subjects were placed in the left lateral position in a 70-cm wide bore MR scanner (view of the front face of the scanner) (a). A platform was used to maintain the knee joint flexion-extension motion in the sagittal plane (view from the back of the scanner) (b). A weight (1.1 kg) at the end of a pulley system provided a small amount of resistance to the motion (view of the back face of the scanner) (c).

Grahic Jump Location
Fig. 2

Analysis technique. Muscle-tendon paths were digitized and joint angles measured on sagittal images during flexion and extension (a). Length measurements (circles) were fit with a third order polynomial (line) for flexion and extension motions separately (b). Moment arms were determined by taking the derivative of the polynomial fit with respect to joint angle [14] (c).

Grahic Jump Location
Fig. 3

Rectus femoris knee muscle moment arms. Average rectus femoris muscle moment arms (solid line) plotted over joint angle with shaded standard deviation measured during flexion (a) and extension (b). Data from published cadaveric measurements during dynamic joint motion [1] (dashed line) are plotted over the same range for comparison. Note that cadaver data were averaged across multiple flexion and extension motions.

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