Equine Articular Cartilage Stiffness Determination Using Indentation

In order to determine that the stiffness varies between different joint types, an indentation test was performed on fresh equine articular cartilage surfaces from the fetlock, carpal, and stifle joints. The results demonstrated that the stiffness varies on different joints showing different mechanical behaviors. A flat-ended cylindrical indenter is lowered at a constant rate for 20 s until the indentation depth reaches 0.2 mm (velocity of 10 mu m/s). It was shown that the articular cartilage of the fetlock is stiffer than the carpal and stifle joints. The average stiffness of the fetlock, carpal, and stifle joints are 46.1 N/mm, 20.5 N/mm, and 2.73 N/mm, respectively. The coefficients of a fit for the joints were statistically compared as well using the student t-test. The differences of some coefficients between the fetlock, carpus, and stifle were "very highly significant" (p<0.001). Four different surfaces in the fetlock and four in carpal joint were compared as well. The front lateral, front medial, rear lateral, and rear medial cartilage surfaces in the fetlock were not significantly different in stiffness. In the carpus, the distal radius and proximal radial carpal bone articular cartilage surfaces showed significantly different stiffness from the others, while the distal radial carpal bone and proximal third carpal bone articular cartilage surfaces possessed similar stiffness values. The cartilage surfaces from the radiocarpal joint were stiffer than the midcarpal joint. Clear trends in the correlations between stiffness and weight as well as stiffness and age of the horse were not observed.