Assessment of morphological, acoustic and mechanical properties of enzymatically-degraded articular cartilage using high frequency ultrasound

In this study, high frequency ultrasound and ultrasound-assisted mechanical testing systems were used to quantitatively measure the morphological, acoustic and mechanical properties of normal and enzymatically degraded bovine articular cartilages in vitro, in order to assess its potential application in assessing the early osteoarthritis (OA) related cartilage degeneration. Forty (n = 20 × 2) osteochondral cartilage disks were prepared from 20 bovine patellae and divided into 2 groups for later collagenase and trypsin digestions, respectively. A high frequency ultrasound system was used to analyze the surface roughness (URI), thickness and acoustic parameters (including IRC, IA, IBS, AIB_bone) of the articular cartilage before and after enzymatic degradations. A newly developed water jet ultrasound indentation system was used to assess the mechanical properties of the cartilage samples. The results showed that URI increased significantly (p < 0.05) after collagenase digestion, while this was not the case after trypsin digestion (p > 0.05). URI significantly also correlated with optical roughness index (ORI, p < 0.05). IRC decreased significantly (p < 0.05) after collagenase digestion, but not for trypsin digestion (p > 0.05). Both enzymatic degradation groups showed significant increase in IBS (p < 0.05) after treatments. The stiffness measured showed that articular cartilage from both groups became significantly softer (p < 0.05) after treatments. A linear relationship was founded between IRC and URI (p < 0.05). To conclude, this study showed that high frequency ultrasound can be potential as a comprehensive tool to quantitatively and systematically analyze the morphological, acoustic and mechanical properties of articular cartilage in association with its OA-associated degeneration.