OBJECTIVETo observe the effects of low-intensity pulsed ultrasound (LIPUS) on repairing extracellular matrix in rabbit knee osteoarthritis and analyze its mechanism.

METHODSSixty adult female rabbits with an average weight of (2.0 ± 0.2) kg, were divided randomly into two groups (experimental group and control group, 30 rabbits in each group). All rabbits were replicated in right knees by Hulth method for knee osteoarthritis model. Two weeks after operation, the rabbits in experimental group were treated with LIPUS, and the ultrasonic frequency was (800 ± 5%)KHz and the maximum intensities of spatially averaged and time averaged (SATA) was (50 ± 10%) mw/cm2, for 1 time a day and every time 20 min, while the rabbits in control group were treated with sham LIPUS,the same operation with experimental group but without energy output. At the 2, 4, 8 weeks after treatment, 10 rabbits in each group were randomly killed for each time. The general changes of cartilage and its histopathological changes by HE staining were observed; the expression of collagen type II, proteoglycan, MMP-3, 7, 13 in cartilage were analyzed by immunohistochemical and RT-PCR technique; and the expression of NO in cartilage was analyzed by nitrate reduction method.

RESULTSOn the same observed time point, the damage degree of cartilage in experimental group was slighter than that of control group (P < 0.01), the expression of MMP-3, 7, 13 and NO in cartilage in experimental group was lower than that of control group (P < 0.01) while collagen type II and proteoglycan was higher than that of control group (P < 0.01).

CONCLUSIONLow-intensity pulsed ultrasound can repair the damaged cartilage by reducing the expression of MMP-3, 7, 13, inhibiting the secretion of NO and promoting the synthesis of collagen type II and proteoglycan in cartilage.