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Research Papers

The Effect of Size and Location of Tears in the Supraspinatus Tendon on Potential Tear Propagation

[+] Author and Article Information
James Thunes

Department of Bioengineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260

R. Matthew Miller

Department of Bioengineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260
Orthopaedic Robotics Laboratory,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260

Siladitya Pal

Department of Mechanical and
Industrial Engineering,
Indian Institute of Technology,
Roorkee 247667, India

Sameer Damle

Department of Chemical Engineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260

Richard E. Debski

Department of Bioengineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260
Orthopaedic Robotics Laboratory,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260
Department of Orthopedic Surgery,
University of Pittsburgh,
Pittsburgh, PA 15260

Spandan Maiti

Department of Bioengineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260
Department of Chemical Engineering,
Swanson School of Engineering,
University of Pittsburgh,
Pittsburgh, PA 15260
e-mail: spm54@pitt.edu

1Corresponding author.

Manuscript received December 24, 2014; final manuscript received May 26, 2015; published online June 23, 2015. Assoc. Editor: Kristen Billiar.

J Biomech Eng 137(8), 081012 (Aug 01, 2015) (8 pages) Paper No: BIO-14-1645; doi: 10.1115/1.4030745 History: Received December 24, 2014; Revised May 26, 2015; Online June 23, 2015

Rotator cuff tears are a common problem in patients over the age of 50 yr. Tear propagation is a potential contributing factor to the failure of physical therapy for treating rotator cuff tears, thus requiring surgical intervention. However, the evolution of tears within the rotator cuff is not well understood yet. The objective of this study is to establish a computational model to quantify initiation of tear propagation in the supraspinatus tendon and examine the effect of tear size and location. A 3D finite element (FE) model of the supraspinatus tendon was constructed from images of a healthy cadaveric tendon. A tear of varying length was placed at six different locations within the tendon. A fiber-reinforced Mooney–Rivlin material model with spatial variation in material properties along the anterior–posterior (AP) axis was utilized to obtain the stress state of the computational model under uniaxial stretch. Material parameters were calibrated by comparing computational and experimental stress–strain response and used to validate the computational model. The stress state of the computational model was contrasted against the spatially varying material strength to predict the critical applied stretch at which a tear starts propagating further. It was found that maximum principal stress (as well as the strain) was localized at the tips of the tear. The computed critical stretch was significantly lower for the posterior tip of the tear than for the anterior tip suggesting a propensity to propagate posteriorly. Onset of tear propagation was strongly correlated with local material strength and stiffness in the vicinity of the tear tip. Further, presence of a stress-shielded zone along the edges of the tear was observed. This study illustrates the complex interplay between geometry and material properties of tendon up to the initiation of tear propagation. Future work will examine the evolution of tears during the propagation process as well as under more complex loading scenarios.

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Copyright © 2015 by ASME
Topics: Stress , Tendons
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References

Figures

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Fig. 2

Experimental versus simulated stress–strain curves. The dashed line shows the experimental response of a representative tendon in uniaxial tension. An 8 mm tear located in the anterior region 5 mm from the lateral edge was used to determine the material parameters (solid line). The extents of the shaded region show the range of the stress–strain response for all cases tested. The response for the one material case is shown with open triangles.

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Fig. 4

Stress in the ML direction for tears 5 mm from the lateral edge with an applied stretch of 1.12. The areas directly around the tear are shown. Significant stress concentrations are seen at the tips of the tear. The magnitude of the stress concentrations is not the same between anterior and posterior tips or between different tears.

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Fig. 1

Geometry and boundary conditions. (a) Two lines of tears at 5 and 10 mm from the lateral surface (representing the tendon insertion) are defined. A tear will be placed at either the posterior (P), middle (M), or anterior (A) location. For the different sizes, the out tip of the tear will be constant for the posterior and anterior tears. For the middle tears, the midpoint will be constant across sizes. (b) The boundary conditions and representative mesh (8062 nodes and 36,670 four-noded tetrahedral elements). The lateral surface is fixed. A displacement is applied to the medial surface. Movement in the AP and bursal directions is also fixed at the medial surface. The mesh shows an initially zero thickness tear (8 mm long) in the middle location 5 mm from the lateral surface.

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Fig. 3

Tendon with an 8 mm anterior tear 5 mm from the lateral edge. A stretch of 1.15 is applied to the medial edge. The contours show the ML strain component (a) and the ML stress component (b).

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Fig. 5

Stress in the ML direction for tears 5 mm from the lateral edge. The stress contours have been scaled such that low stress regions are shown in black. There are large regions of low stress at the flanks of the tears. This region grows as the tear size increases. Further, the region lateral to the tear has significantly higher area than the region medial to the tear.

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