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Research Papers

The Impact of Glenoid Labrum Thickness and Modulus on Labrum and Glenohumeral Capsule Function

[+] Author and Article Information
Nicholas J. Drury

Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219drury.nick@gmail.com

Benjamin J. Ellis

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112u0241427@utah.edu

Jeffrey A. Weiss

Department of Bioengineering, University of Utah, Salt Lake City, UT 84112jeff.weiss@utah.edu

Patrick J. McMahon

Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219mcmahonp@upmc.edu

Richard E. Debski

Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219genesis1@pitt.edu

J Biomech Eng 132(12), 121003 (Nov 01, 2010) (7 pages) doi:10.1115/1.4002622 History: Received March 31, 2010; Revised September 14, 2010; Posted September 27, 2010; Published November 01, 2010; Online November 01, 2010

The glenoid labrum is an integral component of the glenohumeral capsule’s insertion into the glenoid, and changes in labrum geometry and mechanical properties may lead to the development of glenohumeral joint pathology. The objective of this research was to determine the effect that changes in labrum thickness and modulus have on strains in the labrum and glenohumeral capsule during a simulated physical examination for anterior instability. A labrum was incorporated into a validated, subject-specific finite element model of the glenohumeral joint, and experimental kinematics were applied simulating application of an anterior load at 0 deg, 30 deg, and 60 deg of external rotation and 60 deg of glenohumeral abduction. The radial thickness of the labrum was varied to simulate thinning tissue, and the tensile modulus of the labrum was varied to simulate degenerating tissue. At 60 deg of external rotation, a thinning labrum increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 10.5% average strain) and anterior band (increased 7.5% average strain). These results suggest a cause-and-effect relationship between age-related decreases in labrum thickness and increases in labrum pathology. A degenerating labrum also increased the average and peak strains in the labrum, particularly in the labrum regions of the axillary pouch (increased 15.5% strain) and anterior band (increased 10.4% strain). This supports the concept that age-related labrum pathology may result from tissue degeneration. This work suggests that a shift in capsule reparative techniques may be needed in order to include the labrum, especially as activity levels in the aging population continue to increase. In the future validated, finite element models of the glenohumeral joint can be used to explore the efficacy of new repair techniques for glenoid labrum pathology.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 3

The effect of modifying the labrum thickness at joint positions with a 25 N anterior load applied at 60 deg of glenohumeral abduction and 0 deg, 30 deg, and 60 deg of external rotation. L-AB, L-AP, and L-PB=labrum regions of the anterior band of the inferior glenohumeral ligament, axillary pouch, and posterior band of the inferior glenohumeral ligament, respectively (average±standard deviation of element strains within a labrum or capsule region).  ∗ statistical significance and difference greater than 3.5% strain.

Grahic Jump Location
Figure 4

The effect of modifying the labrum modulus at joint positions with a 25 N anterior load applied at 60 deg of glenohumeral abduction and 0 deg, 30 deg, and 60 deg of external rotation. L-AB, L-AP, L-PB=labrum regions of the anterior band of the inferior glenohumeral ligament, axillary pouch, and posterior band of the inferior glenohumeral ligament, respectively (average±standard deviation of element strains within a labrum or capsule region).  ∗ statistical significance and difference greater than 3.5% strain.

Grahic Jump Location
Figure 2

(A) Anterior view of subject-specific finite element model (left shoulder). (B) Labrum regions added for current study.

Grahic Jump Location
Figure 1

Sample CT image of left shoulder with the joint in the reference position. The image depicts the difficulty in differentiating between the soft-tissue structures at the insertion of the capsule into the glenoid.

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