Influence of applied stress on energy dissipation and crack growth in articular cartilage

Mechanical stress-induced damage to the articular cartilage can result in fracture initiation or significant tissue degeneration leading to osteoarthritis (OA) compromising joint mobility. Despite the clinical significance, a comprehensive understanding of the crack progression in cartilage damage remains elusive due to complex mechanical responses and variable initial crack geometry. This study investigated the impact of physiologically relevant stress levels, ranging from light-weight to high stress activities, on crack propagation in cartilage under compressive cyclic loading. Through empirical analysis, interconnections between localized damage (crack growth) and global damage (changes in material properties) across various levels of applied stress were established. Microscale cracks were nucleated in cylindrical cartilage plugs extracted from porcine patella specimens via microindentation and then subjected to controlled cyclic loading to examine changes in structural integrity, mechanical properties, and crack extension. Results demonstrated a decrease in cartilage thickness and apparent stiffness with increasing stress levels, indicative of bulk material damage. Dynamic mechanical properties such as energy dissipation and phase angle showed an overall reduction after fatigue loading. Crack growth followed an empirical law with increasing applied stress, reflective of greater mechanical damage at higher stress values. The findings of the study showed the interplay between global and local damage in cartilage under cyclic loading, suggesting insights into the fundamental changes occurring within the tissue. The outcomes of this investigation contributed to detailed understanding of the cartilage fatigue behavior through empirical laws and could potentially serve to prevent or delay tissue degeneration in OA.