Effects of chondrocyte shape and orientation on continuous ultrasound propagation in microscale articular cartilage.

We apply the finite element method (FEM) to model the propagation of ultrasound waves in the extracelluar matrix (ECM) of the cartilage tissue, and quantify the effects of chondrocyte geometry and orientation, material properties, and ultrasound frequency on the deformations in the ECM. The computational domain consists of a 2-D ECM layer with embedded chondrons. The interactions of elliptical chondrons with the ultrasound waves are quantified for frequencies in the 0.5 MHz to 4 MHz range. Three orientations are considered for the elliptical chondrocytes-horizontal, vertical, or at a 45º angle. Chondron orientation significantly influences the attenuation of ultrasound amplitudes, with the horizontal chondrons being the most effective. The screening effects of chondrons are also a function of depth in the ECM layer. In the superficial zone, chondrons at 45º angle are more effective in screening ultrasound waves at all frequencies, while in the deep zone, these chondrons show a frequency-dependent behavior.