Development and phantom test of a minimized water-jet ultrasound indentation system for arthroscopic measurement of articular cartilage integrity

The detection of early degeneration of the articular cartilage is an important step to stop, delay or even reverse this otherwise irreversible process when detected in its advanced or late stage. A water-jet ultrasound indentation system has been previously developed in our group for assessing the articular cartilage integrity. This study aims to further design a minimized water-jet ultrasound indentation probe intended for the arthroscopic measurement of the articular cartilage status. The probe was constructed by installing a 10 MHz ultrasound transducer (Φ = 3 mm) at the tip of a plastic rod (Φ = 12 mm) with an axial hole for generating the water jet (Φ = 2 mm). Preliminary test was performed on 28 phantoms with various stiffness values. A stiffness coefficient was calculated by a linear fitting of the force/deformation curve obtained from the indentation system. Results showed that the stiffness coefficient measured from the current system (0.625 ± 0.488 N/mm) agreed well with that from a rigid-contact mechanical indentation test (0.730 ± 0.631 N/mm) with a high correlation (r2= 0.98, p < 0.001). Therefore, it was concluded that the performance of this water-jet indentation system was comparable to the conventional indentation. The incorporation of ultrasound in the minimized indentation system can further assess the morphologic and acoustic properties, thus enabling a compound characterization of the articular cartilage integrity under arthroscopic control.