Biomechanical properties of mature porcine anterior cruciate ligaments (ACL) and the impact of cyclic loading

Background Experimental modelling is required to test novel anterior cruciate ligament (ACL) grafts. Porcine ACLs resemble human ACLs regarding in situ force distribution and anatomic characteristics. However, their essential properties remain unclear. This study describes essential baseline porcine ACL properties and determines the impact of standardised cyclic loading. Methods Twenty mature porcine cadaver knee joints were used for standardised biomechanical testing. Axial tensile loading was performed, and force to failure (F max ), elongation, stiffness, yield point, and absorbed energy by ACL ligament were determined. Baseline values were compared with samples exposed to cyclic loading (10.000 runs). Results Dimensions were determined by computed tomography (CT) scanning. ACLs showed a mean F max of 720.5 N ± 108.6 N, whereas a mean F max of 614.9 N ± 98.1 N was found upon cyclic loading, p = 0.07. Stiffness did not differ between groups (baseline: 76.9 N/mm ± 8.9 N/mm vs. after cyclical loading: 76.1 N/mm ± 9.5 N/mm, p = 0.8). Furthermore, sample elongation during cyclic loading was unaltered. A biphasic pattern of ACL rupturing, reflecting two separate porcine bundles, was identified. Conclusion Two separate porcine bundles have been identified as being in line with humans. The robust results of this study underline the applicability of this model to the human condition. Moreover, specific features of porcine ACL may form a template for developing synthetic ligaments and tailored treatment protocols.