The supraspinatus tendon is often involved in rotator cu↵ tears. The pathogenesis of such tears is not well known and can be multicausal (mechanical, inflammatory, ...). The idea of this project was to analyse the mechanical contribution to rotator cuff tears with a numerical deformation analysis of the supraspinatus tendon. The tendon was simulated under tension in two conditions: an isotropic case and an anisotropic case. In the isotropic case, the tendon was simulated with the same material properties in every direction. In the anisotropic case, the tendon’s fiber were computed and the material was defined in the fiber direction and in the transverse direction. In the isotropic case, the strain was found to be higher in the two studied position (90 ̊abduction and rest position) than in the anisotropic case. In both cases (isotropic and anisotropic) the maximal strain is situated at the distal side of the tendon insertion on the humeral head. The di↵erence in the strain value is due to the fact that the isotropic material definition is averaged in all direction and therefore is softer in the fiber direction and stronger in the transverse direction. The isotropic model is herefore not very consistant with a real tendon structure. Both models are consistent with clinical observations as supraspinatus tears occur usually at the distal side of the insertion. However, for qualitative deformation analysis an anisotropic material choice is recommended.