How Age Affects the Failure Properties of Human Meniscus: High-Speed Strain Mapping of Tears

Tears to the human knee meniscus are one of the most frequent orthopedic injuries in young and older populations, with over a half-million meniscus surgeries performed in the U.S. each year. The meniscus is composed of an anisotropic fiber network that is primarily aligned circumferentially to resist the tensile or hoop stresses that develop during joint compression. Meniscal tears can either disrupt this fiber network (e.g. radial and flap tears) or propagate in the ground substance alongside the fibers (e.g. horizontal and vertical tears). The incidence of these tear patterns is influenced by age, but it is unknown whether the effect of age on meniscal injury epidemiology is due to changes in the mechanical properties of the meniscus, or due to other physiological factors. Prior studies in similar tissues have shown that collagen cross-links accumulate with age, resulting in increased fibril stiffness potentially reducing tissue ductility and altering failure behavior. In order to more accurately measure tissue deformation and failure behavior, digital image correlation (DIC) paired with high-speed video to determine the strains at which tears initiate, as well as to quantify how a tear propagates across a material surface until total failure. The angle at which tears propagate relative to the loading axis relates to the physical mechanism of failure, and can be used to describe and predict the physical limits of a material. This technology can therefore provide insight into the effect of age on failure mechanisms, and help advance our understanding of this prevalent and costly injury.

 

Objective. The objective of this study was to determine the effect of age on the anisotropic tensile failure properties of the human lateral meniscus. We hypothesize that 1) meniscus ductility decreases with age, and 2) meniscus tears occur on the plane of maximum shear strain.