Effects of Different Low-Intensity Pulsed Ultrasound Intensities and Durations on a Post-Traumatic Knee Joint Contracture Model in Rats

This study aimed to investigate the low-intensity pulsed ultrasound (LIPUS) therapeutic effects on knee joint dysfunction after immobilization following trauma and to identify the optimum LIPUS intensity and duration. A knee post-traumatic joint contracture (PTJC) model was established in male Wistar rats divided into three groups: front irradiation (n = 4), medial irradiation (n = 3), and sham (n = 3). LIPUS irradiation was performed for 20 min/day (30 mW/cm2 [spatial average temporal average] SATA, 1 MHz, duty cycle of 20%, 5 times/week, for 2 weeks). PTJC model rats were also divided into LIPUS and sham groups with LIPUS performed at different intensities (30 or 120 mW/cm2 SATA) and durations (5 or 20 min). The range of motion (ROM) of the knee joint with skin and muscles (knee ROM) and without (knee joint intrinsic ROM) and the length of the posterior joint capsule and the intra-articular adhesion of the knee joint were evaluated. Knee ROM and knee joint intrinsic ROM were significantly larger in the front LIPUS group (p < 0.01). The length of the posterior capsule was significantly higher in the LIPUS groups (p < 0.01), but no significant differences between the LIPUS groups were observed. The intra-articular adhesion length was significantly lower in the 120 mW/cm2–20 min group than those in the 30 mW/cm2–5 min group (p < 0.01). The effects on LIPUS intensity and duration to intra-articular adhesion were not synergistic but additive. LIPUS therapy may be a rehabilitation approach for preventing knee joint dysfunction after trauma or surgical invasion.