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. 2009 Sep;37(9):1831-9.
doi: 10.1177/0363546509334222. Epub 2009 May 29.

Interaction between the supraspinatus and infraspinatus tendons: effect of anterior supraspinatus tendon full-thickness tears on infraspinatus tendon strain

Nelly Andarawis-Puri  1 , Eric T Ricchetti, Louis J Soslowsky
Affiliations

Interaction between the supraspinatus and infraspinatus tendons: effect of anterior supraspinatus tendon full-thickness tears on infraspinatus tendon strain

Nelly Andarawis-Puri et al. Am J Sports Med. 2009 Sep.

Abstract

Background: Rotator cuff tears are common and not well-understood shoulder problems. Structural and mechanical inhomogeneity of the supraspinatus tendon complicates accurate prediction of risk of tear propagation and may affect appropriate clinical treatment.

Hypothesis: We propose that interactions between the supraspinatus and infraspinatus tendons are critical to load bearing at the glenohumeral joint and warrant investigation.

Study design: Controlled laboratory study.

Methods: Principal strains in the infraspinatus tendon of cadaveric human shoulders were evaluated with increasing anterior full-thickness supraspinatus tendon tear sizes and loading to evaluate whether a mechanical interaction between the supraspinatus and infraspinatus tendons exists. A constant nominal load was attached to the infraspinatus throughout all experimental conditions.

Results: Increasing supraspinatus tendon tear width from intact and 33% to 66% and increasing supraspinatus tendon load caused an increase in maximum and a decrease in minimum principal strain in the infraspinatus tendon. Increasing the supraspinatus tendon tear size from intact to 33% of the width had no significant effect on infraspinatus tendon strain.

Conclusion: Supraspinatus and infraspinatus tendons mechanically interact. The observed significant increase in maximum and decrease in minimum principal strain was concurrent in both the infraspinatus and supraspinatus tendons.

Clinical relevance: Changes in infraspinatus tendon strain associated with increases in supraspinatus tendon tear size and loading may shield a torn supraspinatus tendon from further injury or may have an effect on the load-bearing capacity of the infraspinatus tendon. Results also imply that the effect of a small tear that does not compromise the confluent region between the supraspinatus and infraspinatus tendon may be localized, eliminating its effect on infraspinatus tendon strain.

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Figures

Figure 1
Figure 1
Schematic representation of experimental setup. Two cameras were used in this study, with one camera optimally positioned to capture deformations in the insertion site of the supraspinatus tendon and the other camera optimally positioned to capture deformations in the insertion site of the infraspinatus tendon.
Figure 2
Figure 2
The region of interest for strain analysis in the infraspinatus tendon is shown in white. (A) The image resolution was approximately 0.05mm/pixel. (B) The distal, superior and inferior borders are defined by the natural edges of the tendon, and the proximal border is approximately 12mm proximal to the distal edge.
Figure 3
Figure 3
A) Average maximum principal strain in the infraspinatus tendon significantly increases with increasing supraspinatus tendon loading. B) Average minimum principal strain in the infraspinatus tendon significantly increases with increasing supraspinatus tendon loading
Figure 4
Figure 4
A) Average maximum principal strain in the infraspinatus tendon significantly increases with increasing supraspinatus tendon tear size. B) Average minimum principal strain in the infraspinatus tendon significantly increases with increasing supraspinatus tendon tear size.
Figure 5
Figure 5
Apparent average maximum principal strain increases with increasing supraspinatus tendon tear size and load. A common symbol above any two bars is indicative of a significantly difference between the pair of bars for the effect of tear size.
Figure 6
Figure 6
Apparent average minimum principal strain decreases with increasing supraspinatus tendon tear size and load. A common symbol above any tow bars is indicative of a significant difference between the pair of bars for the effect of tear size.
See this image and copyright information in PMC

References

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