High-resolution ultrasound elastography of articular cartilage in vitro

Articular cartilage is comprised of three histologic zones that exhibit different Young's moduli. In addition, with age and disease the moduli can be altered. Therefore,diagnosis of joint diseases can be accomplished by detecting biomechanical properties of articular cartilage. In this report we investigate the feasibility of ultrasound elastography of bovine articular cartilage (n=5) employing instantaneous static compression using high-resolution (55MHz) ultrasound elastography in vitro as a potential arthroscopic technique. Elastograms were computed using cross-correlation technique and a gradient operator. The elastograms revealed near-zero strains within the samples, except at the articular surface and the interface between zones 1 and 2. The boundary conditions associated with the loading technique implemented herein that have to allow for a large acoustic window during imaging represent a fundamental challenge toward imparting local strains to the articular cartilage. Despite the complex boundary conditions, the feasibility of imaging strain within the cartilage during a sustained compression using elastographic techniques was demonstrated.