Rotator cuff tendon strain correlates with tear propagation.

Rotator cuff tears are a common tendon injury often requiring surgical treatment. Understanding the relationships between tear size, tendon loading, and tendon strain adjacent to a rotator cuff tear can provide important insights into predicting the likelihood of propagation to larger tears which would influence clinical treatment. Previous studies assume that an increase in strain correlates with an increase in risk of tear propagation. However, these studies did not explicitly investigate these important relationships. Therefore, the objective of this study was to quantify two-dimensional strain fields adjacent to a rotator cuff tendon tear under loading to failure and to assess the relationship between tendon strain and tear size. Sheep infraspinatus tendons were used to evaluate the effect of tear size on principal strains in the region adjacent to the tear. The relationship between strain, tear propagation, and the direction of tear propagation was quantified. Results showed that principal strains linearly correlated with tear propagation and that tear propagation began at strains as low as 1.7%. In addition, tears propagated in the direction of highest maximum and lowest minimum principal strain. Finally, maximum and minimum principal strains were higher and lower, respectively, adjacent to larger tears compared to smaller tears. Findings from this study validate the use of local strain adjacent to a rotator cuff tear as an indicator of the risk and direction of tear propagation.