Rotator cuff tears may be due in part to the complex loading environment of the supraspinatus tendon (SST). Previous research has reported inhomogeneous uniaxial tensile mechanical properties of human SST [1–2] and location-specific collagen fiber alignment distributions that are qualitatively more disperse than other tendons [3–4]. Our group recently measured fiber alignment under load of samples tested along the tendon long-axis and found that re-alignment occurs in the toe-region and varies by SST location [5]. However, the mechanical properties and effect of fiber alignment under more complex loads remain unknown. Examining the properties of SST when tested transverse to the tendon long-axis will evaluate tissue anisotropy and better elucidate possible mechanisms for tissue inhomogeneity and nonlinearity. Therefore, the objectives of this study are to 1) measure local fiber alignment during transverse tensile loading, 2) measure corresponding mechanical properties, and 3) examine structure-function relationships of SST. We hypothesize that 1) fibers will become less aligned during transverse testing, 2) mechanical properties will be greatest in the anterior and bursal locations, and 3) higher initial alignment will correspond to lower transverse tensile properties.

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