Ultrasonic characterization of articular cartilage.

Osteoarthrosis is the most important joint disease that threatens health of the musculoskeletal system of elderly people. Today, there is a need for sensitive, quantitative diagnostic methods for successful and early diagnosis of the disorder. In the present study, we aimed at evaluating the applicability of ultrasound for quantitative assessment of cartilage structure and properties. Bovine articular cartilage was investigated both in vitro and in situ using high frequency ultrasound. Cartilage samples were also tested mechanically in vitro to reveal relationships between acoustic and mechanical parameters of the tissue. The collagen organization and proteoglycan content of cartilage samples were mapped, using quantitative polarized light microscopy and digital densitometry, respectively, to reveal their effect on the acoustic properties of tissue. The high frequency pulse-echo ultrasound (20-30 MHz) technique proved to be sensitive in detecting the degeneration of the superficial collagen-rich cartilage zone. In addition, ultrasound was found to be a potential tool for measuring cartilage thickness. When the results from biomechanical indentation measurements and ultrasound measurements of normal and enzymatically degraded articular cartilage were combined, collagen or proteoglycan degradation in the tissue could be sensitively and specifically differentiated from each other. To conclude, high frequency ultrasound is a useful tool for evaluation of the quality of superficial articular cartilage as well as for the measurement of cartilage thickness. Therefore, ultrasound appears to be a valuable supplement to the mechanical measurements of articular cartilage stiffness.