Biomechanics of aging and osteoarthritic human knee ligaments

Background Ligaments work to stabilize the human knee joint and prevent excessive movement. Whilst ligaments are known to decline in structure and function with aging, there has been no systematic effort to study changes in gross mechanical properties in the four major human knee ligaments due to osteoarthritis (OA). This study aims to collate material properties for the anterior (ACL) and posterior (PCL) cruciate ligaments, medial (MCL) and lateral (LCL) collateral ligaments. Our cadaveric samples come from a diverse demographic from which the effects of aging and OA on bone and cartilage material properties have already been quantified. Therefore, by combining our previous bone and cartilage data with the new ligament data from this study we are facilitating subject-specific whole-joint modelling studies. Methods The demographics of the collected cadaveric knee joints were diverse with age range between 31 to 88 years old, and OA International Cartilage Repair Society grade 0 to 4. Twelve cadaveric human knee joints were dissected, and bone-ligament-bone specimens were extracted for mechanical loading to failure. Ligament material properties were determined from the load-extension curves, namely: linear and ultimate (failure) stress and strain, secant modulus, tangent modulus, and stiffness. Results There were significant negative correlations between age and ACL linear force ( p=0.01 ), stress ( p=0.03 ) and extension ( p=0.05 ), ACL failure force ( p=0.02 ), stress ( p=0.02 ) and extension ( p=0.02 ), PCL secant ( p=0.02 ) and tangent ( p=0.02 ) modulus, and LCL stiffness ( p=0.05). Significant negative correlations were also found between OA grades and ACL linear force ( p=0.05 ), stress ( p=0.02 ), extension ( p=0.01 ) and strain ( p=0.03 ), and LCL failure stress ( p=0.05 ). However, changes in age or OA grade did not show a statistically significant correlation with the MCL tensile parameters. Trends showed that almost all the tensile parameters of the ACL and PCLs decreased with increasing age and progression of OA. Due to small sample size, the combined effect of age and presence of OA could not be statistically derived. Conclusions This research is the first to correlate changes in tensile properties of the four major human knee ligaments to aging and OA. The current ligament study when combined with our previous findings on bone and cartilage for the same twelve knee cadavers, supports conceptualization of OA as a whole-joint disease that impairs the integrity of many peri-articular tissues within the knee. The subject-specific data pool consisting of the material properties of the four major knee ligaments, subchondral and trabecular bones and articular cartilage will aid reconstruction and graft replacements and advance knee joint finite element models, whilst knowledge of aged or diseased mechanics may direct future therapeutic interventions