BACKGROUND:Articular cartilage injuries can result from a variety of causes. Conventional therapy cannot obtain the optimal clinical results. Low-intensity pulsed ultrasound has been shown to promote the repair of injured articular cartilage. OBJECTIVE:To investigate the effects of low-intensity pulsed ultrasound on the repair of injured articular cartilage. METHODS:Twenty New Zealand white rabbits were used to establish knee arthritis models and equal y randomized into study and control groups, respectively. Rabbits in the study group received low-intensity pulsed ultrasound treatment, and sham low-intensity pulsed ultrasound treatment was given in the control group. At 8 weeks after treatment, pathological change and histological scores in articular cartilage tissue col ected from both groups were determined. Moreover, the ultrastructure and type II col agen expression of chondrocytes were determined. Matrix metal oproteinase-13 mRNA expression was detected by quantitative real-time PCR. RESULTS AND CONCLUSION:At 8 weeks after treatment, toluidine blue staining showed a disordered arrangement of cel s, decreased number of cartilage cel s in each layer and cluster in the control group. Light disordered arrangement of cel s, decreased appearance of the superficial layer cel s and the cluster phenomenon were observed in the study group. Articular cartilage tissue scores were significantly decreased in the study group compared with the control group (P<0.05). The chondrocytes were smal , enlarged intracel ular mitochondria and rough endoplasmic reticulum, cytoplasmic swel ing, col agen fibrils coarse, wel developed Golgi apparatus, and nuclear fragmentation were observed in the control group. In addition, the normal structure of organel es disappeared and cel degeneration was observed in the control group. In the study group, the size of chondrocytes and the Golgi complex and other organel es were normal, and the protein polysaccharide granules were observed in the cytoplasm and membrane. The mRNA expression of matrix metal oproteinase-13 in the study group was significantly lower than that in the control group (P<0.05). Type II col agen immunoreactivity in the study group was stronger than that in the control group. No incision infection, suppuration, red swel ing appeared in al rabbits. Our results suggest that low-intensity pulsed ultrasound can be used for the treatment of articular cartilage injury by al eviating the degradation of col agen type II and inhibiting the expression of matrix metal oproteinase-13.