Ultrasonic propagation properties of articular cartilage at 100 MHz

A pilot study on articular cartilage assessed the contribution of individual matrix components to ultrasound propagation. The influence of collagen fibril orientation and collagen crosslinking was also assessed. Sections of adult bovine articular cartilage taken both parallel and perpendicular (cross sections) to the articular surface were examined using the scanning laser acoustic microscope (SLAM) operating at an ultrasonic frequency of 100 MHz. A set of samples was evaluated that had been sequentially treated by enzymes to (1) remove 85% of the chondroitin sulfate; (2) remove remaining GAGs, glycoproteins, and other noncollagen proteins, leaving only the collagen fibril network; and (3) disrupt the collagen intermolecular crosslinks. Two striking observations were made: a profound effect of the “preferred” collagen fibril orientation on acoustic wave speed and a marked increase in attenuation coefficient when intermolecular crosslinks were broken in the collagen. [This work was supported by NIH Grants AM21557, CA36029, and AR36794 and Rehabilitation Research and Development Services of the Veterans Administration.]