Correlation between signalment and the biphasic hyperelastic mechanical properties of equine articular cartilage

The correlation between mechanical properties from the equine articular cartilage and signalment was investigated. Fresh articular cartilage of fetlock, carpus, and stifle were harvested from 12 deceased horses with information on the breed, age, sex, and weight within 4 h of euthanasia for measurements. Seven indentation tests at different normalized displacements of 10, 20, 30, 35, 40, 45, and 50% of the cartilage thickness were performed with a spherical probe indenting at 0.1 mm/s velocity. The solid matrix of the cartilage was found to follow a hyper-elastic material behavior defined by Ogden; the solid phase aggregate modulus (Ea), hyperelastic material constant (α), and fluid load fraction (F′) of the cartilage were characterized. The characterized material properties were statistically analyzed using a mixed model ANOVA and Scheffe's test to check the correlation between the properties and signalment variables (breed, age, sex, and weight). There were correlations between both the solid phase aggregate modulus and age (p < 0.0392) and weight (p < 0.0375). The fluid load fraction also correlated with both age (p < 0.0146) and weight (p < 0.0003). Breed and sex were not statistically significant variables affecting the variation of theses material properties. No statistically significant correlations between the hyperelastic material constant and the signalment variables were observed.