Mechanical properties of articular cartilage: variation with depth

Abstract

The response of human, adult articular cartilage to compressive loading has been investigated in this study. Full thickness specimens of patellar cartilage were subjected to compressive loading either in a Scanning Electron Microscope (SEN) or in one of the two conventional testing machines. Testing in the SEM meant that video recordings could be made of the deformation which occurred during loading, and subsequent analysis of these video recordings enabled the determination of the variation in the mechanical properties through the thickness of the cartilage. Testing of individual slices of cartilage and repeated testing of specimens reduced in thickness by the removal of successive slices of cartilage were performed in the conventional testing machines. The results of these tests also give an indication as to the variation in mechanical properties with depth. Results indicate that the compliance of normal patellar cartilage is highest in the superficial zone, decreases to a minimum in the mid-zone and increases again slightly in the deep zone. The full thickness tests were used to determine the effect (if any) of age, site of specimen, storage procedure and variations in water and uronic acid content on the response of the tissue. These results show that the compliance of articular cartilage is highly dependent on the age of the tissue, increasing with age, and that specimens stored at - 20ºC show, on average, a higher value of compliance than specimens stored at + 4ºC. No systematic variation in compliance of specimen with site was observed and there was no correlation between either water or uronic acid content and compliance.