Alleviation Effects and Mechanisms of Low-intensity Focused Ultrasound on Pain Triggered by Soft Tissue Injury

Objectives Pain caused by soft tissue injury (STI) is always intractable and will eventually result in physical and psychological problems. This experiment aimed to assess the efficacy and mechanisms of low-intensity focused ultrasound (LIFU) for pain-related STI. Methods Rabbits (n = 30) with STI were given fixed treatment for 20 seconds and then mobile treatment for 60 seconds daily for 10 consecutive days by an LIFU device with a power output of 5 to 6 W and a frequency of 0.8 MHz. To evaluate the degree of pain, the levels of beta-endorphin in serum were measured by an enzyme-linked immunosorbent assay before and 5 to 10 minutes after the 1st, 3rd, 7th, and 10th treatments. The pain threshold was measured by an electronic analgesy meter on the 1st, 3rd, 7th, 10th, 17th, and 24th days after the start of the treatment. To investigate inflammation, prostaglandin E-2, interleukin-1 beta, and 5-hydroxytryptamine levels were detected by an enzyme-linked immunosorbent assay, and nuclear factor kappa B messenger RNA levels were determined by a real-time quantitative polymerase chain reaction at the same time as the pain threshold was tested. Results Compared with non-LIFU groups, beta-endorphin levels and pain thresholds were significantly increased (P < .05), whereas nuclear factor- kappa B messenger RNA, prostaglandin E-2, interleukin- 1 beta, and 5-hydroxytryptamine levels were significantly reduced (P < .05) after LIFU treatment in rabbits with STI. Conclusions Low-intensity focused ultrasound can alleviate pain induced by STI and could have further clinical applications.