Fig. 6.

(A) Idealized FE model of the tendon-bone complex based on measured geometrical features at the rat shoulder. The numbers indicate: (1) the bone-mineralized cartilage interface, (2) the tidemark between mineralized fibrocartilage (MFC) and unmineralized fibrocartilage (UFC) and (3) the tendon. The right image shows one of the simulated scenarios for the local predominant orientation of collagen fibers, following the outward splay of interface region. (B) Simulated principal stress and strain. Peak values are localized beneath the outward splay of the tendon (as highlighted by the red circles). (C) Anatomical side view (left) and idealized model (right) of the bone-tendon system at the rotator cuff, showing the rotator cuff tendons wrapping around the humeral head. The axisymmetric idealized model comprises the bone, the bone-tendon interface and the tendon. Material properties of bone and tendon were fixed, whereas properties of the interface were allowed varying. The applied radial stress simulated muscle loading. (D) Variation of normalized radial stress (along the radial direction) for unmineralized (tendon like), fully mineralized (bone like), and linearly graded interface region. In all cases, stresses are substantially higher than the applied stress. This happens not only at the interface but also within the bone and the tendon. (E) Distribution of material properties (i.e., radial elastic modulus, tangential elastic modulus and Poisson ratio of the insertion) resulting from the minimization of radial stress. A compliant region (with stiffness lower than tendon and bone) appears at the interface. Allowing Poisson ratio to vary across the insertion has an effect only on the tangential modulus. Figures modified from (Thomopoulos et al., 2006; Liu et al., 2012), with permission.