Pertinence of Sheep Knee Joint for Calibration of Ligaments’ Constitutive Equations; Experimental and Theoretical Study

The knee joint is one of the most complex joints in human body because of its complex geometry and articulations. On the other hand, due to many practical constraints for studying the anatomy and biomechanics of the human knee, in vivo and in vitro animal models have been widely used. Based on this fact, an objective comparison of the sheep samples especially from mechanical behavior point of view is needed. Therefore, a purpose of the present study is to evaluate priority of usage of sheep specimens via comparing the biomechanical differences of normal ligaments between sheep and human. To this end, some experimental tensile tests have been done on the different knee ligaments of sheep including hyperelastic behavior of the anterior cruciate ligament, medial collateral ligament, posterior cruciate ligament, and lateral collateral ligament. So, an objective comparison of the sheep and human samples has been done. Furthermore, the magnitude of material constants of different hyperelastic constitutive equations including 3rd order Ogden, Yeoh and Fung–Demiray models, as well as the maximum experienced stress by the knee ligaments have been considered.