Tensile properties of a split supraspinatus tendon
The supraspinatus (SSP) tendon contributes specifically to abduction and stability of the humeral head and is the most common site of rotator cuff tears. Morphologically, the SSP tendon is not a single fusiform tendon but consists of two subregions, anterior and posterior.
In this study, the authors demonstrated significant differences in the ultimate failure load and the ultimate stress between these two sub-regions: the posterior sub-region of the SSP was significantly weaker than the anterior.
These results suggest that the SSP is more easily torn in the posterior than the anterior region if both sub-regions undergo the same stress. Regarding the supraspinatus muscle, the anterior SSP tendon receives the loading of approximately 70% of the muscle fibers. In vivo, the stress applied to the anterior sub-region of the SSP tendon is approximately 230% that to the posterior. This ratio between muscular load distributions to the anterior and posterior regions of the SSP tendon is close to the ratio of the ultimate failure stresses between the two sub-regions. This matching of ratios suggests that the morphological and mechanical differences between the sub-regions serve a functional purpose.