On the effect of measurement uncertainties on estimated knee ligament properties from laxity measurements

We investigate how noise during laxity trials affect optimisation-based estimations of knee ligament properties. One subject-specific knee model with known ligament properties was created. Four sets of laxity trials, with an increasing number of load cases, were simulated and uniform noise ([-0.5, 0.5] (mm and degrees)) were added to the resulting kinematics. Stiffness and reference strain for ACL, PCL, MCL, and LCL were estimated from 20 samples of noisy kinematics. Stiffness error ranges of 6 kN, 8 kN, 9 kN, and 4 kN; reference strain error ranges of 3 %, 3 %, 2 %, and 2 % for ACL, PCL, MCL, and LCL, respectively, were found for the three sets of laxity tests (7, 13, and 22 load cases). The laxity test with 60 load cases resulted in stiffness and reference strain error ranges below 500 N and 1 %.