Modeling the Viscoelastic Load Share Between Knee Porcine Ligaments

A former analytical elastic model, of the load share between porcine knee ligaments, is enhanced with the inclusion of the viscoelastic approach. Experimental tests were performed to obtain the necessary Fung’s model constants. The following knee porcine ligaments were used: lateral collateral ligament (LCL), anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) and medial collateral ligament (MCL). The final objective of the proposed analytical model is to estimate the load share between porcine knee ligaments, in both elastic and viscoelastic phases. Preliminary conclusions show that the load share rearrangement after viscoelastic phase is quite discreet, but the reduction of the ligaments force resistance capacity becomes very significative. In fact, the force values that the ligaments can resist drop around half of its initial value. Probably, this fact explains why newly operated knee ligaments, which are apparently tight just after the operations, can develop an unstretched state, in a couple of weeks.