Many studies have proved that LIPUS therapy is an excellent conservative therapeutic approach for bone and cartilage tissues (6, 11, 12). Among the non-surgical therapy alternatives for tendon injuries, the use of LIPUS is one of the most explored. However, no research demonstrating the efficacy of the treatment supported by in vivo investigations exist. There is currently no agreement on the parameters for therapeutic ultrasound treatment, and the evidence on the clinical efficacy of therapeutic ultrasound on tendinopathy is still being finalized.
The fact that the longest examination period was determined as day 45 and the examination could not be performed at later times constituted our study's limitations. Additionally, because there were so many groups, the number of subjects per group was restricted to 6, and samples could not be taken at separate times with different treatment durations in the groups where treatment was started in the early and late acute phases.
The change in muscle temperature was monitored throughout a 10-minute treatment with 1 MHz and 3 MHz therapeutic ultrasound using thermistors placed at various depths (5 cm or less). The findings demonstrate that therapeutic ultrasonic treatments at 1-MHz and 3-MHz led to a time- and dose-dependent rise in tissue temperature (13–15). When the ultrasonic intensity was increased from 1.5 W/cm2 to 3.0 W/cm2 (1 MHz frequency), he discovered that skin and subcutaneous tissues warmed(16).
In modelling, they used therapeutic ultrasound for 5 weeks, 4 minutes per day, three days a week, at a frequency of 3 MHz, with an intensity of 1 W/cm2. On the seventh day following surgery, they began the temporal planning of the treatment, and three weeks later, the immobilization with a plaster cast came to an end. At the end of this research, they discovered that even at high doses and frequencies, they could not get favorable results (17)
In modeling made to measure the effect of continuous therapeutic ultrasound on Achilles tendinopathy in rabbits, it was discovered that the tendon's tensile strength and capacity to absorb energy had significantly improved after treatment with 3 MHz continuous therapeutic ultrasound at 1 W/cm2 for 5 minutes (18). Another study demonstrated that identical outcomes for tendon treatment may be obtained with a lower dosage of 0.5 W/cm2 (19).
In a different study, Achilles tendons were completely severed, sutured, and then, following immobilization, ultrasound therapy was administered. The tensile strength of completely severed and healed rat Achilles tendons was shown to be higher in the group that received therapeutic ultrasounds nine days following the operation (18, 19). In a study, therapeutic ultrasound was used at a modest dose (0.5 W/cm2) for 5 minutes each day to simulate post-rupture treatment in rat Achilles tendons. They acquired healing characteristics that seemed to be significantly higher in the low-dose therapeutic ultrasound group compared to the control group in light of biochemical and biomechanical findings (20). There was no evidence of increased tendon strength in rabbits treated with pulsed ultrasound for six weeks at a dosage of 0.8 W/cm2 (21).
Another study found that treatment partly ruptured Achilles tendons with low-dose (1.0 W/cm2) and high-dose (2.0 W/cm2) therapeutic ultrasound led to higher mean power in the high-dose group compared to the low-dose group (22). The findings of their modeling, which involved continuously treating the tendon with therapeutic ultrasound at a power density of 1 W/cm2 for four minutes per treatment session, demonstrated that ultrasound treatment accelerated the rate at which rats' damaged Achilles tendons were repaired. These outcomes also support the hypothesis that tendon restoration leads to greater stretch due to increased collagen synthesis (23).
In our study, we opted to use a device (IGEA SpA, Carpi, Italy) that generates low-intensity pulsed ultrasound with parameters for the LIPUS technique that include ultrasound frequency of 1.5 MHz, pulse width of 200 µseconds, repetition rate of 1 kHz, and SATA (Spatial Average-Temporal Average) acoustic intensity of 30 mW/cm2. In order to conveniently examine the phases taking place in the healing process, we adopted the Achilles tendinopathy model published in the literature, which is built with a single dosage of 3 mg/ml type 1 collagenase injection (7).
According to our research, the end of the inflammatory phase of healing and the start of the proliferation phase is when LIPUS treatment in the tendinopathy model produces the best outcomes. One week of treatment is adequate compared to two weeks to have the same effects. Compared to pathology results, successful biomechanical outcomes of LIPUS therapy are seen earlier. With LIPUS therapy, it takes about 53% less time to reach the biomechanically statistically significant modulus of elasticity level and about 30% less time to attain the tensile strength and toughness values. The degree of inflammation is attained roughly 53% faster and the pathologically relevant fibrillar appearance is reached around 33% faster with LIPUS treatment.
Based on the results, it is concluded that samples should be given time for pathological examination in future research since cellular changes cannot occur as quickly as biomechanical changes and that the effect on pathology results is seen 1 week after the completion of the therapy.
When we initially planned the groups for our experiment, we anticipated that LIPUS treatment in the early and late acute phases would provide less successful results than the start of treatment in the mid-acute phase group. From this perspective, the timing of the start of treatment was the most important variable in the speed of recovery.
In conclusion, even a single week of timely LIPUS treatment speeds up recovery. It has been a promising and conservative treatment approach, considering the rapid pace of life and the expectations of patients. We think that the positive outcomes of our study will serve as a model for subsequent clinical research.