4The inhomogeneous and anisotropic mechanical properties and structural components 5 of articular cartilage (AC) may cause complex acoustic properties in this important 6 tissue. In this study, we used 50 MHz ultrasound to measure in vitro the depth-
The objective of this study was to investigate the feasibility of ultrasonic monitoring for 5 the transient depth-dependent osmotic swelling and solute diffusion in normal and degenerated articular cartilage (AC) tissues. Full-thickness AC specimens were collected from fresh bovine patellae. The AC specimens were continuously monitored using a
The change of the ultrasound (US) speed in articular cartilage (artC) under applied strain conditions may induce some measurement errors of the mechanical properties of the artC during both indentation and compression tests using US. In this paper, the strain dependence of the US speed in bovine artC (n = 20) under compression in vitro was investigated by virtue of using a custom-made US-compression testing system. The US speeds of the artC at the instant after the compression and that after a period of stressrelaxation were estimated under the applied strain ranged from 0 % to 20 %. Moreover, the instantaneous modulus and the modulus after the stress-relaxation of the artC were measured and correlated with the US speeds. There was no significant difference (p > 0.05) between the US speeds at the instant after the compression and that after the stressrelaxation, even though there was a discrepancy between the instantaneous modulus and the modulus after stress-relaxation. The US speed was found to be highly correlated to the applied strain (r 2 = 0.98, p < 0.001) in a quadratic relation and changed by 7.8 % (from 1581 ± 36 m/s to 1671 ± 56 m/s) when the applied strain reached 20 %. The results revealed that the strain dependent effect on the US speed in artC should be considered when the US is deployed for the assessment of artC using the compression or indentation test.
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.
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