Effect of low-intensity pulsed ultrasound therapy on a rat knee joint contracture model

[Purpose] Histopathological investigation of the effects of low-intensity pulsed ultrasound (LIPUS) on joint components using a rat knee joint contracture model. [Subjects and Methods] Nineteen, 9-week-old Wistar male rats were divided into a control group (n=6) and an experimental group. Rats in the experimental group underwent cast immobilization of the right rear limb for 8 weeks. They were then randomly divided into a non-treatment group (n=6), which was raised under normal conditions for 4 weeks, and a treatment group (n=7), which underwent LIPUS for 4 weeks. LIPUS irradiation was performed at a frequency of 3 MHz, an intensity of 30 mW/cm², and a pulse rate of 20% duty cycle. Irradiation was performed once daily for 10 min, 5 days per week. At the end of this period, tissue specimens in which the knee sagittal plane could be observed were prepared and observed using an optical microscope. [Results] The extension-limiting angle of the knee joint was significantly less in the treatment group compared with the non-treatment group. The posterior joint capsule was significantly thicker only in the non-treatment group, and the density was 53.5 ± 7.5% for the control group, 77.2 ± 5.7% for the non-treatment group, and 69.2 ± 2.9% for the treatment group, with significant differences existing across all groups. [Conclusion] LIPUS may widen the space between collagen fiber bundles of the joint capsule, thereby improving the range of motion.