Determination of the compressive material properties of the supraspinatus tendon

A methodology was developed for determining the compressive properties of t he supraspinatus tendon, based on finite element principles. Simplified thr ee-dimensional models were created based on anatomical thickness measuremen ts of unloaded supraspinatus tendons over 15 points. The tendon material wa s characterized as a composite structure of longitudinally arranged collage n fibers within an extrafibrillar matrix. The matrix was formulated as a hy perelastic material described by the Ogden form of the strain energy potent ial. The hyperelastic material parameters were parametrically manipulated u ntil the analytical load-displacement results were similar to the results o btained from indentation testing. In the geometrically averaged tendon, the average ratio of experimental to theoretical maximum indentation displacem ent was 2.00 (SD: 0.01). The average normalization of residuals was 2.1g (S D: 0.9g). Therefore, the compressive material properties of the supraspinat us tendon extrafibrillar matrix were adequately derived with a first-order hyperelastic formulation. The initial compressive elastic modulus ranged fr om 0.024 to 0.090 MPa over the tendon surface and increased nonlinearly wit h additional compression. Using these material properties, the stresses ind uced during acromional impingement can be analyzed.