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Research Papers

The Influence of Partial and Full Thickness Tears on Infraspinatus Tendon Strain Patterns

[+] Author and Article Information
Kayt E. Frisch

Department of Engineering,
Dordt College,
498 4th Ave SE,
Sioux Center, IA 51250
e-mail: kayt.frisch@dordt.edu

David Marcu

Sauk Prairie Memorial Hospital,
Prairie du Sac, WI 53578
e-mail: dmarcu@spmh.org

Geoffrey S. Baer

Department of Orthopedics and Rehabilitation,
University of Wisconsin,
Madison, WI 53705
e-mail: baer@ortho.wisc.edu

Darryl G. Thelen

Department of Biomedical Engineering,
Department of Mechanical Engineering,
University of Wisconsin,
Madison, WI 53705
e-mail: thelen@engr.wisc.edu

Ray Vanderby

Departments of Orthopedics and Rehabilitation
and Biomedical Engineering,
University of Wisconsin,
Madison, WI 53705
e-mail: Vanderby@ortho.wisc.edu

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received August 16, 2013; final manuscript received January 17, 2014; accepted manuscript posted February 6, 2014, published online April 10, 2014. Assoc. Editor: Kristen Billiar.

J Biomech Eng 136(5), 051004 (Apr 10, 2014) (6 pages) Paper No: BIO-13-1371; doi: 10.1115/1.4026643 History: Received August 16, 2013; Revised January 17, 2014; Accepted February 06, 2014

Tears on the bursal and articular sides of the rotator cuff tendons are known to behave differently and strain is thought to play a role in this difference. This study investigates the effect of tear location on the changes in three strain measurements (grip-to-grip, insertion, and mid-substance tissue) in a sheep infraspinatus tendon model during axial loading. We introduced a 14 mm wide defect near the insertion from either the articular or bursal side of the tendon to three depths (3 mm, 7 mm & full) progressively. For each condition, tendons were sinusoidally stretched (4% at 0.5 Hz) while insertion and mid-substance strains were tracked with surface markers. For a fixed load, grip-to-grip strain increased significantly compared to intact for both cuts. Insertion strain increased significantly for the bursal-side defect immediately but not for the articular-side until the 66% cut. Mid-substance tissue strain showed no significant change for partial thickness articular-side defects and a significant decrease for bursal-side defects after the 66% cut. All full thickness cuts exhibited negligible mid-substance tissue strain change. Our results suggest that the tendon strain patterns are more sensitive to defects on the bursal side, and that partial thickness tears tend to induce localized strain concentrations in regions adjacent to the damaged tissue.

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References

Figures

Grahic Jump Location
Fig. 1

The width and thickness designations used for tendon defect creation. (a) The top view of the tendon showing the width of the tendon and indicating the position of the small and large defects. (b) The side view of the tendon, indicating bursal and articular sides of the tendon and the thickness across the footprint.

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Fig. 2

Sheep infraspinatus tendon optical test setup. Sheep infraspinatus bone-tendon segments were mounted in a custom bath affixed to a servo-hydraulic mechanical testing machine.

Grahic Jump Location
Fig. 3

Optical strain processing. (a) Tissue motion was imaged using markers placed on the bursal surface of the tendon (b) images were converted binary format to locate each marker in the imaging plane. (c) Marker centroid trajectories were tracked over time (centroid path). Displacements were then spatially differentiated to calculate strain in the tendon tissue.

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Fig. 4

Markers used for computing optical strain (a) at the insertion site, (b) within the tendon issue

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Fig. 5

Strain results by defect group. {Average (±1SE) strain at 60 N load for large bursal and articular defects. Grip-to-grip strains for (a) the bursal-sided defect (BS) and (b) articular-sided defect (AS) are significantly (p < 0.05) greater than intact for all cut depths. Insertion strain for (c) the BS group and (d) the AS group show even more dramatic increases with cut depth. Tissue strain for (e) the BS group does not change significantly for any cut, though the average does decrease to nearly zero for 66% and full-thickness cuts. Conversely, tissue strain increases significantly for both articular-sided cuts before dropping to nearly zero for the full-thickness cut. A summary of P-values is shown in Table 1. The * indicates a statistically significant (p < 0.05) difference between the two groups.

Grahic Jump Location
Fig. 6

Change in average (±1 SE) strain measures (at 60 N of load) due to 33%, 66%, and full thickness cuts. Bursal-sided partial defects compromised overall tendon stiffness more than articular sided defects, resulting in more significant increases in grip-to-grip and tissue strain. Changes in insertion strains were substantially smaller for both bursal and articular differences. P-values are shown in Table 2.

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