Ultrasonic measurement of articular cartilage swelling: Preliminary results

Articular cartilage (AC) is a biological weight-bearing tissue covering the bony ends of articulating joints. Subtle changes in structure or composition can lead to degeneration of AC such as in osteoarthritis. Currently, there is a lack of reliable diagnostic techniques for early signs of osteoarthritis. The objective of this study was to use ultrasound to probe the transient depth-dependent swelling of AC in vitro, and ultimately to develop a new approach for the early assessment of osteoarthritis. A 50 MHz ultrasound system was used to collect reflected and scattered echoes from AC specimens. The displacements of selected portions of ultrasound signals were measured using a cross-correlation tracking approach. Osteochondral cylinders prepared from fresh bovine patellae were used in this study. During a test, the AC specimen was fixed in a testing chamber filled with saline solution. AC swelling was induced by either changing the concentration of the saline solution or emerging dehydrated AC specimens into the saline solution. Our preliminary results demonstrated that ultrasound could be used to reliably monitor the transient depth-dependent swelling induced by both approaches. It was found that water was gradually absorbed by the AC, first in the superficial layer, and then deep layer. The ultrasound speeds of AC tissues bathed in different saline solutions were different.