Equine subchondral bone failure threshold under impact compression applied through articular cartilage.

This study examines the resilience of the subchondral bone, found beneath the cartilage in horse joints, under high-impact stress. The research ultimately offers an estimated threshold for initial bone tissue failure due to impact compression, offering potential applications in future studies and interventions for joint health.

Objective and Methodology

• The research looks at the degree and mechanism of microdamage to the subchondral bone, which lies beneath the articular cartilage, in horse knees due to high-impact loading. This damage is a significant contributing factor to knee osteoarthritis.
• The team used mechanical impact testing on equine cartilage-bone and then created a finite element model (μFEM) for each sample based on micro CT imaging data.
• The team aimed to determine the elastic tissue modulus and the local stresses and strains associated with micro-fractures within the bone. The model’s material properties were adjusted iteratively to match the predicted stress-strain curves with the actual experimental results.

Note: The elastic tissue modulus refers to the inherent elasticity of a tissue when subjected to stress, and it is indicative of the tissue’s stiffness.

Assumptions and Results

• The researchers made an assumption of isotropic homogeneous material properties for both uncalcified cartilage and the subchondral bone. The uncalcified cartilage’s large deformation was simulated using hyperelastic material properties.
• The resulting shear for the uncalcified cartilage and tissue elastic modulus for the subchondral bone were calculated as G=38±20MPa and E(t)=3.3±0.7GPa respectively.
• The results suggested that initial failure in the subchondral bone occurred at local tensile and compressive stresses of 29.47±5.34 MPa and 64.3±21.3MPa, and tensile and compressive strains of 1.12±0.06% and 1.99±0.41%, respectively.

Applications and Implications

• The determined tissue-level material properties can be used in future finite element modeling of similar joints subjected to impact loading.
• The results can assist in designing artificial bone-cartilages to replace damaged tissue in the joint.
• Overall, the study provides a baseline for understanding the initial failure threshold in subchondral bone tissue due to impact compression transmitted through the overlying articular cartilage.

Note: This threshold is the maximum amount of stress these tissues can undergo before failure (damage) occurs.