Ultrasonic propagation properties of articular cartilage at 100 MHz.

A pilot study on articular cartilage assessed the contributions of individual matrix components to ultrasound propagation. The influence of collagen fibril orientation and collagen cross linking was also assessed. Sections of adult bovine articular cartilage cut both parallel and perpendicular 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 glycosaminoglycans, glycoproteins, and other noncollagen proteins, leaving only the collagen fibril network; and (3) disrupt the collagen intermolecular cross links. Two striking observations were made: a profound effect of the "preferred" collagen fibril orientation on ultrasonic speed and a marked increase in attenuation coefficient when intermolecular cross links were broken in the collagen.