Site dependence of thickness and speed of sound in articular cartilage of bovine patella

Researchers have made efforts to quantify thickness of articular cartilage as well as its acoustic and mechanical properties using various ultrasound (US) techniques during the last decades, because they are important indicators of articular cartilage degeneration. However, the variation of the thickness and speed of sound of articular cartilage at different anatomical sites would result in the uncertainty of US assessment of degeneration. In this paper, the site dependences of speed of sound and thickness of bovine patellar articular cartilage (n = 10) were investigated using a custom-made US measurement system. The thickness and speed of sound of articular cartilage at different locations of the bovine patella were measured on excised specimens ex situ using a noncontact US approach. A total of 10 patellae were tested. The results showed the overall mean value of the speed of sound in the articular cartilage at the 25 measured sites was 1626 ± 86 m/s (range, 1507 to 1834 m/s). No statistically significant difference in the speed of sound was observed among the 25 locations or among the four quadrants of the patella. The highest speed of sound (1834 ± 74 m/s) was obtained at the medial-upper quadrant and the lowest value (1507 ± 74 m/s) at the medial-lower quadrant. Further grouping of the data revealed that the speed of sound in the central region (1633 ± 21 m/s) was significantly (p < 0.01) larger than that for the surrounding region (1621 ± 22 m/s). The overall mean thickness of the patellar articular cartilage was 1.34 ± 0.34 mm. No significant difference was obtained in the thickness among the 25 locations and also among the four quadrants. However, when the thickness values were divided diagonally, a significant difference (p < 0.01) was observed between the upper region (1.27 ± 0.11 mm) and the lower region (1.31 ± 0.41 mm) of the patellae. Although no significant differences in the thickness and speed of sound among the tested sites were observed, it was demonstrated in this study that they did show some degree of site dependence.