Miniaturized Water-Jet Ultrasound Indentation System for Quantitative Assessment of Articular Cartilage Degeneration: A Validation Study

Osteoarthritis is a common joint disease affecting a large population especially the elderly where cartilage degeneration is one of its hallmark symptoms. There is a need to develop new devices and instruments for the early detection and treatment of cartilage degeneration. In this study, we describe the development of a miniaturized water-jet ultrasound indentation probe for this purpose. To evaluate the system, we applied it to characterize the degeneration of articular cartilage with the measurement of its morphologic, acoustic, and mechanical properties, using the enzymatic digestions of cartilage as a model of OA. Fifty cartilage samples were tested with 10 of them used for the reproducibility study and the other 40 for collagenase and trypsin digestions. Thickness, integrated reflection coefficient (IRC), effective stiffness, and energy dissipation ratio (EDR) were used to quantify the change of articular cartilage before and after degeneration. The measurement reproducibility as represented by the standardized coefficient of variation (SCV) was 2.6%, 10.2%, 11.5%, and 12.8% for thickness, IRC, stiffness, and EDR, respectively. A significant change of IRC, stiffness, and EDR was detected after degeneration by the designed probe (p < 0.05). There was also a significant difference of IRC, stiffness, and EDR between trypsin and collagenase digestions (p < 0.001). In conclusion, a miniaturized water-jet ultrasound indentation probe has been designed, which has been successfully used to detect and differentiate cartilage degeneration simulated by enzymatic digestions. This probe, with future development, can be potentially suitable for quantitative assessment of cartilage degeneration with an arthroscopic operation.