Therapeutic effect and underlying mechanism of low-intensity focused ultrasound on knee arthrofibrosis in rats

To assess the therapeutic efficacy of low-intensity focused ultrasound (LIFU) on knee arthrofibrosis in rats and explore its underlying mechanisms.

Fifteen male SD rats (8 weeks old, weighing 250~300 g) were randomly divided into a blank control group, a model group, and an ultrasound treatment group, with 5 animals in each group. Rat model of knee joint stiffness was established in the model and ultrasound treatment group. The rats in the ultrasound group received LIFU intervention (frequency: 1 MHz, power: 1.5 W, 20 min per session, 5 times/week) for 4 weeks. The knee ranges of motion (ROM, flexion and extension) were measured in all 3 groups at 0, 14 and 28 d after intervention. Histological analysis was conducted for the morphological changes in the posterior capsular area of the knee. After the synovial fibroblasts were primary isolated from rat knee joints, the cells were divided into blank control, LIFU, TGF-β (10 ng/mL), and TGF-β+LIFU groups. Changes in fibrosis-related indicators and the TGF-β/Smad signaling pathway were assessed in each group.

In the animal experiments, LIFU intervention for 14 d resulted in significantly improved flexion-extension ROM in knee joints when compared with the rats in the model group (P<0.05), and the improvement was more obvious at 28 d after intervention (P<0.05). After 28 d of LIFU intervention, the fibrosis of the posterior capsule of the knee joint was notably improved in the ultrasound group than the model group, and the expression levels of fibrosis-related indicators (α-SMA, TGF-β) were decreased (P<0.05). In the cellular experiments, the TGF-β group exhibited remarkable up-regulation of fibrosis-related molecules (α-SMA, COL1A1, COL3A1) at both protein and mRNA levels (P<0.05), and activation of the TGF-β/Smad signaling pathway when compared to the blank control group. While LIFU intervention inhibited the expression of TGF-β-induced upregulation of fibrotic indicators (α-SMA, COL1A1, COL3A1) and the activation of TGF-β/Smad signaling pathway (P<0.05).

LIFU can effectively improve knee arthrofibrosis in rats, which potentially through the inhibition of fibroblast activation and modulation of the TGF-β/Smad signaling pathway.