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Research Papers

Strain Distribution of Intact Rat Rotator Cuff Tendon-to-Bone Attachments and Attachments With Defects

[+] Author and Article Information
Ryan C. Locke

Department of Biomedical Engineering,
University of Delaware,
5 Innovation Way,
Newark, DE 19716
e-mail: rlocke@udel.edu

John M. Peloquin

Department of Biomedical Engineering,
University of Delaware,
161 Colburn Lab 150 Academy Street,
Newark, DE 19716
e-mail: peloquin@udel.edu

Elisabeth A. Lemmon

Departments of Animal and Food Sciences
and Biomedical Engineering,
University of Delaware,
5 Innovation Way,
Newark, DE 19716
e-mail: blemmon@udel.edu

Adrianna Szostek

Departments of Animal and Food Sciences
and Biomedical Engineering,
University of Delaware,
5 Innovation Way,
Newark, DE 19716
e-mail: aszostek@udel.edu

Dawn M. Elliott

Mem. ASME
Department of Biomedical Engineering,
University of Delaware,
161 Colburn Lab 150 Academy Street,
Newark, DE 19716
e-mail: delliott@udel.edu

Megan L. Killian

Mem. ASME
Department of Biomedical Engineering,
University of Delaware,
5 Innovation Way,
Newark, DE 19716
e-mail: killianm@udel.edu

1Corresponding author.

Manuscript received August 14, 2017; final manuscript received September 14, 2017; published online October 16, 2017. Editor: Beth A. Winkelstein.

J Biomech Eng 139(11), 111007 (Oct 16, 2017) (6 pages) Paper No: BIO-17-1361; doi: 10.1115/1.4038111 History: Received August 14, 2017; Revised September 14, 2017

This study aimed to experimentally track the tissue-scale strains of the tendon–bone attachment with and without a localized defect. We hypothesized that attachments with a localized defect would develop strain concentrations and would be weaker than intact attachments. Uniaxial tensile tests and digital image correlation were performed on rat infraspinatus tendon-to-bone attachments with defects (defect group) and without defects (intact group). Biomechanical properties were calculated, and tissue-scale strain distributions were quantified for superior and inferior fibrous and calcified regions. At the macroscale, the defect group exhibited reduced stiffness (31.3±3.7 N/mm), reduced ultimate load (24.7±3.8 N), and reduced area under the curve at ultimate stress (3.7±1.5 J/m2) compared to intact attachments (42.4±4.3 N/mm, 39.3±3.7 N, and 5.6±1.4 J/m2, respectively). Transverse strain increased with increasing axial load in the fibrous region of the defect group but did not change for the intact group. Shear strain of the superior fibrous region was significantly higher in the defect group compared to intact group near yield load. This work experimentally identified that attachments may resist failure by distributing strain across the interface and that strain concentrations develop near attachment defects. By establishing the tissue-scale deformation patterns of the attachment, we gained insight into the micromechanical behavior of this interfacial tissue and bolstered our understanding of the deformation mechanisms associated with its ability to resist failure.

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References

Figures

Grahic Jump Location
Fig. 1

Study design. Infraspinatus attachments were divided into two experimental groups: intact and defect. For the defect group, a biopsy punch was used to create a superior-edge, partial-width, full-thickness tendon-to-bone attachment defect. Uniaxial tensile tests were performed with simultaneous image capture to obtain: biomechanical properties, qualitative tissue-scale strain fields, and quantitative regional tissue-scale strain of intact and defect groups. For regional tissue-scale strain, the average median strain was compared for fibrous, calcified, superior, and inferior regions within and between intact and defect groups. The white cylinder represents the biopsy punch used to create the defect. The dashed rectangle is a zoomed in depiction of the attachment. The dashed circle represents the superior edge defect. The dashed line separates superior from inferior, and the solid line separates the fibrous attachment from the calcified attachment; together creating the four quadrants. T, tendon; B, bone; M, muscle.

Grahic Jump Location
Fig. 2

Biomechanical strength and AUC at ultimate stress decreased in tendon-to-bone attachments with defects. Structural properties of (a) ultimate load and (b) stiffness significantly decreased in the defect group compared to the intact group. (c) AUC at ultimate stress significantly decreased in the defect group, while other material properties of (d)–(f) Young’s modulus, strain at ultimate stress, and ultimate stress were not significantly different between groups. Black lines indicate significant difference (p < 0.05); data shown are mean ±95% confidence intervals.

Grahic Jump Location
Fig. 3

Near yield load, tissue-scale strain was heterogeneous and concentrated at attachment defects. Representative strain fields for (a), (c), and (e) intact and (b), (d), and (f) defect attachments are shown. Longitudinal (εxx; (a) and (b)), transverse (εyy; (c) and (d)), and shear (εxy; (e) and (f)) strain fields were generated near yield load. Strain magnitude is represented by the colored scale bars. Images shown are representative for each group. Coordinates for measured strain are shown in panel C. (a) and (b) T, tendon; B, bone. (b), (d), and (f) The defect is marked with a dashed white circle.

Grahic Jump Location
Fig. 4

Near yield load, transverse and shear strain were concentrated in the fibrous region of attachments with defects. Average Median tissue-scale (a) longitudinal strain (εxx), (b) transverse strain (εyy), and (c) shear strain (εxy) were compared between intact and defect groups for the fibrous and calcified regions of tendon-to-bone attachments. Black lines indicate significant difference (p < 0.05). Data shown are average median strain ±95% confidence intervals.

Grahic Jump Location
Fig. 5

Near yield, shear strain localizes near tendon-to-bone attachment defects. (a) Average median tissue-scale transverse and (b) shear strain for the superior and inferior fibrous regionswere compared. Black lines indicate significant difference (p < 0.05); data shown are average median strain ±95% confidence intervals.

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