Quantitative assessment of arthritic cartilage using high-frequency ultrasound

The current study aims at evaluating the ability of 55 MHz ultrasound (US) in assessing subtle cartilage changes during the time course of a model of arthritis induced in rat knees (intra-articular injection of Zymosan). Arthritic (n=24) and control (n=24) patellae were explored in vitro at 5, 14 and 21 days post-injections, using a 3-D US microscope. Cartilage thickness was measured on B-scan images. Changes in cartilage surface and matrix, and in cartilage/bone interface were characterized by the integrated reflection coefficient (IRC) and apparent integrated backscatter (AIB), respectively. US findings were compared to histologic results. Thickness of arthritic cartilage decreased at D5 (p<0.05), then increased at D14 (p<0.O5), but was similar to that of controls at D21. IRC mean values of Zymosan groups decreased significantly (p<0.O5) at D5 and D14, but did not vary at D21. IRC decrease was related to cartilage surface fibrillation. AIB from cartilage/bone interface increased significantly at D5 and D21 (p<0.05) due probably to changes in the interface morphology and/or structure. No significant change was observed in AIB from cartilage matrix. Current results show that 55 MHz US allows detection of lesions involving both cartilage and subchondral bone, as well as of partial restoration of cartilage.