Posterior Cruciate Ligament Retains Its Mechanical Function in Osteoarthritic Human Knees

In total knee arthroplasties (TKA), commonly performed due to osteoarthritis-related pain, the posterior cruciate ligament (PCL) is often preserved. However, it remains poorly understood whether the biomechanical properties of the human PCL are changed at different stages of knee osteoarthritis (OA), i.e. how functional the PCL is in OA-affected knees. The aim of this study was to relate the biomechanical properties of anterolateral (AL) and posteromedial (PM) bundles of human PCLs to knee OA. AL (n=18) and PM (n=18) bundles of human cadaveric (N=9) PCLs were cut to dogbone-shaped samples and subjected to tensile stress-relaxation testing until failure, including a sinusoidal oscillating test at the linear region (8.5–9.5 % strain) of the stress-strain curve at frequencies 0.01, 0.25, 1, and 2 Hz. The equilibrium Young's modulus and strength, as well as the dynamic modulus (describing dynamic material stiffness) and the phase difference (describing viscosity) were determined at each frequency The knee joint OA was characterized by OARSI grades [2] of osteochondral plugs from lateral and medial tibia, anterior and posterior lateral and medial femur, femoral groove and patella. The relationships between biomechanical properties of the bundles and cartilage OARSI grades were investigated with Spearman's rank correlation. In the AL bundle, the Young's modulus, strength, dynamic modulus or phase difference did not correlate with OARSI grade of any site. In the PM bundle, the Young's modulus or strength did not correlate with OARSI grades, but the phase difference at 0.01 Hz frequency negatively correlated with patellar (rho=−0.509, p =0.031, Fig. 2), and at 1 Hz frequency positively with posterior medial femur (rho=0.496, p =0.036) OARSI grade. The changes in PM bundle viscosity may indicate adaptation to more static loads at extension, e.g. reduced activity due to pain, but also adaptation to increased laxity which could cause more rapid straining of PM bundle. The Young's modulus and strength of the bundles exhibited no correlations with osteoarthritic changes, indicating that the core function of the PCL is retained in OA-affected knees. This information may help surgeons in clinical decision making when treating OA patients, e.g. whether to retain or discard the PCL in a TKA surgery. For any figures or tables, please contact the authors directly.