Tear growth mechanisms in high-grade bursal-sided partial thickness tears in the rotator cuff measured with full volume magnetic resonance imaging methods

In this work, we evaluate the mechanical response of rotator cuff tendons with high-grade partial thickness tears through a recently developed full volume measurement technique that resolves through-thickness behavior. As opposed to traditional strain measurement methods, which examine surfaces of the tendon or localized two-dimensional regions, we have probed three-dimensional strains including internal locations via magnetic resonance imaging. Differences between the intact and torn states have been considered in an ex-vivo ovine model of the rotator cuff. The torn condition depicts sliding between cut/uncut tissue regions, with high shear strain concentrations at the boundaries of detached/attached tissue portions. At both submaximal and supramaximal force levels, the internal and inferior bands of the tendon show high shear strain magnitudes, which could indicate regions of high risk for tear propagation. Geometrical features which could explain strain distribution differences in their intact and torn conditions are also analyzed. Through the understanding of full volume displacement and strain distributions, our study elucidates why two-dimensional values might not represent the global behavior of the injured tendon, critical components of the Lagrangian strain tensor which have not been probed before, and important implications for surgical repairs.