Minimally invasive ultrasound method for intra-articular diagnostics of cartilage degeneration

Quantitative ultrasound imaging (QUI) can be used to evaluate the integrity of articular cartilage and for diagnosing the early signs of osteoarthritis (OA). In this study, we applied a minimally invasive ultrasound imaging technique and investigated its ability to detect superficial degeneration of bovine knee articular cartilage. Intact (n=13), collagenase-digested (n=6) and mechanically degraded (n=7) osteochondral samples (dia.=25 mm) and custom-made phantoms with different degrees of surface roughness (n=8) were imaged using a high-frequency (40 MHz) QUI system. For each sample and phantom, the ultrasound reflection coefficient (R), integrated reflection coefficient (IRC) and ultrasound roughness index (URI) were determined. Furthermore, to evaluate the clinical applicability of intra-articular ultrasound (IAUS) in diagnostics, one intact bovine knee joint was investigated ex vivo using a simulated arthroscopic approach. Differences in the surface characteristics of the phantoms were detected by monitoring changes in the reflection and surface roughness parameters. Both mechanically- and enzymatically-induced degradation were sensitively diagnosed by decreased (p<0.05) reflection (R and IRC) at the cartilage surface. Furthermore, mechanical degradation was detected in the increased (p<0.05) surface roughness (URI). The intra-articular investigation of a bovine knee joint suggested that the IAUS technique may enable minimally invasive, straightforward diagnostics of the degenerative status of the articular surfaces. We conclude that quantitative IAUS imaging can be used for detecting collagen disruption and increased roughness of the articular surface. This quantitative in vivo ultrasound technique could have great clinical value in the diagnostics of joint diseases.