Aims: Clinical methods do not provide direct quantitative information about cartilage functional properties. We have developed a novel handheld ultrasound indentation instrument for the diagnosis of articular cartilage degeneration. This study investigates the feasibility and reproducibility of the instrument to evaluate cartilage properties in situ. Methods: Osteochondral blocks (n=18) were prepared from lateral patellar groove (LPG), medial condyle (FMC) and medial tibial (MTP) of bovine knee. In ultrasound indentation, cartilage is indented with an ultrasound transducer. For the determination of cartilage dynamic modulus, tissue thickness and deformation are calculated using ultrasound and stress is measured with strain gauges. High-resolution material tester was used for reference mechanical tests. Cartilage glycosaminoglycan (GAG) content was determined using digital densitometry. Results: Cartilage dynamic modulus was efþciently detected with the novel instrument (r=0.913 with reference values). Dynamic modulus was signiþcantly (p< 0.05) higher at LPG (10.14±3.11 MPa) than at FMC (4.63±1.32 MPa) or MTP (2.92±1.38 MPa). Ultrasound reßection coeff. from the articular surface was signiþcantly smaller at MTP (2.04±0.73%) than at FMC (4.22±0.88%) or LPG(4.43±0.83%). Reproducibility (standardized coeff. of variation) was 3.0%, 5.2% and 1.7% for thickness, dynamic modulus and ultrasound reßection coeff. Cartilage GAG content correlated positively with dynamic modulus (r=0.678) but it was not related with the ultrasound reßection coeff. (r=0.294, p=0.24). Conclusions: Manual measurements were reproducible and the instrument can be used in situ to detect topographical variation of cartilage mechano-acoustic properties. This study establishes a step towards clinical arthroscopic use.

Aims: The objective of this study was to investigate the ability of ultrasound backscattering to detect degeneration of articular cartilage. For this aim, ultrasound B-mode images were acquired from the surfaces of normal and degenerated bovine cartilage samples. Methods: Cylindrical osteochondral samples (n=31) with different degenerative cartilage appearance were prepared from the bovine patellae. Subsequently, degenerative stages of the samples were quantiþed using the Mankin score method. Ultrasound B-mode images of the samples were obtained using a 20 MHz ultrasound instrument (CortexTech.,Denmark).Biomechanical reference measurements were conducted using a stress-relaxation protocol (10% prestrain, 10% strain, 2 mm/s ramp velocity) in unconþned compression geometry. Results: Average reßection coefþcient ( ARC) (r=0.58) and integrated reßection coefþcient ( IRC) (r=0.53) correlated positively with the cartilage dynamic modulus. Furthermore, moduli decreased as a function of Mankin score (r ≤ −0.68). Finally, strong linear correlations were established between the backscattering parameters and the Mankin score (r=−0.79 for the ARC and r =−0.78 for the IRC). Conclusions: Results of this study suggest that ultrasound backscattering from the articular surface is able to diagnose the degeneration of AC. Theoretically, it is also possible to evaluate changes in subchondral bone with the backscatter measurements. In conclusion, ultrasound backscattering, when applied arthroscopically in vivo, may signiþcantly beneþt clinical diagnostics of early osteoarthrosis as well as monitoring of tissue healing after cartilage repair surgery.