Ultrasound speed in articular cartilage under different bathing saline concentration

Ultrasound techniques have recently been widely used for the characterization of articular cartilage (artC) in vitro and in vivo. The sound speed in artC plays an important role either as an indicator for the artC degeneration or for the calculation of other parameters such as tissue thickness or stiffness. Previous studies on artC have been carried out in bathing saline solutions with different concentrations to investigate swelling behaviors of artC. There is a lack of information in the literature about the effect of bathing saline concentration on the sound speed of artC. In the present study we measured sound speed in artC under different saline concentrations ranging from 0M to 2.5M at the room temperature temperature (21±1°C). ArtC specimens from bovine patellar models (n=20) were used in these in-vitro studies. Results demonstrated that the sound speed in artC ranged from 1681±50 m/s to 1816±54 m/s when the saline-concentration varied from 0M to 2.5M, while the sound speed in saline changed from 1521±3 m/s to 1674±3 m/s. The sound speed linearly (r2= 0.99, p <0.001) increased with the increase of the saline concentration at a rate of 55 m/s per mole change. It is concluded that the variations of the bathing saline concentration significantly affect the sound speed in artC and should be well documented in the ultrasonic studies of artC.