A total of 60 patients with KOA were treated with deep thermotherapy combined with dynamic traction in this study. The results revealed significant increases in the post-treatment Lysholm score and significant decreases in the post-treatment VAS scores (20-and 40-day post-treatment scores; P<0.001 in both cases) relative to the pre-treatment values, indicating that the thermotherapy combined with dynamic traction led to significant improvements in knee joint function and significant reduction in pain, respectively. Similarly, results of the high-frequency ultrasound revealed a significant difference in the grade of synovial blood flow signal between the pre- and post-treatment grades, a significant decrease in synovial thickness at 20 and 40 days post-treatment relative to the pretreatment value (P<0.001), and significant decrease in joint effusion at 20 and 40 days post-treatment relative to the pretreatment score (P<0.001).
Currrently, evidence for the use of heat in treating KOA is limited. However, cold application for KOA has been shown to decrease pain, increase joint range, improve the knee’s functional capacity, and increase quality of life [15, 16]. In a study on 100 patients with bilateral KOA treated with short-wave diathermy, the patients exhibited significant decreases in the VAS and Lequesne index scores and better muscle strength compared to patients in the control group . In one study, 110 patients with bilateral primary KOA were received physical treatments with or without heat, diathermy, and ultrasound, and found better improvement in the heat-treated group . However, that study also found no difference in pain and functional parameters in patients treated with short-wave diathermy but instead found improvements in the group treated with hot packs. These results suggest that the approach for heat treatment (i.e. hot pack, short-wave diathermy, or high-frequency thermotherapy) may also influence how the heat is generated and transmitted to the knee joints, consequently affecting the results.
X-ray, computed tomography (CT) scanning, and magnetic resonance imaging (MRI) have been currently used to evaluate effectiveness of treatment of KOA . However, these methods have several limitations. For example, CT scans do not provide much information about cartilage status unless advanced OA has already set in . High-frequency ultrasound examination is more useful to visualize non-bony structures than X-ray  because it can be used to observe changes in lesions and blood supply from various angles, and can thus evaluate the pathological changes of KOA more comprehensively . Additionally, it is more rapid and cost-effective than MRI, and can be performed repeatedly. However, it is highly technique-sensitive, and the operator’s skill could influence the examinations and evaluations substantially. Thus, improving operator skills and standardizing the evaluation procedures could effectively improve the accuracy of evaluation. Azma et al.  and Qvistgaard et al.  exhibited that high-frequency ultrasound could accurately detect lesions in articular cavities and display the conditions of intercondylar cartilage, synovium, and surrounding soft tissues. Wan et al.  and Huang et al.  demonstrated that high-frequency ultrasound could directly display the severity of knee joint cartilage and the lesion characteristics of the synovium and bursa mucosa of the knee joint during rehabilitation treatment of arthritis of the knee joint, assisting in the early detection of cartilage diseases. They also demonstrated that high-frequency ultrasound could be used to measure the depth of joint effusion and synovial thickness and evaluate KOA rehabilitation. Therefore, we used high-frequency ultrasound in the present study to determine joint effusion, synovial thickness, and synovial blood flow grade to evaluate the effectiveness of the treatment.
The present study exhibited that deep thermotherapy combined with dynamic traction could significantly reduce the pain intensity of KOA patients. Cai et al.  reported that the degree of both pain and swelling in patients with KOA improved significantly after traction combined with Pu garlic moxibustion, which were in agreement with the findings of this study. Ma et al.  used high-frequency ultrasound to observe the pre- and post-treatment changes in KOA treated with needle-knife therapy, and observed that the VAS score decreased and that the joint effusion, synovial thickness, and synovial blood flow improved significantly after the therapy, which were concurrent with our findings. The present study exhibited that joint effusion and thickness of synovium and synovial blood flow signal decreased significantly. These findings were mirrored by a study by Guo et al. , suggesting that high-frequency ultrasound could provide objective evidence to evaluate changes in disease condition and to determine treatment efficacy.
The present study used intermittent dynamic constant-force skin traction combined with deep thermotherapy, which could assist the exertion of the effects of deep thermotherapy. Alternating between traction and relaxation could allow the high-frequency electromagnetic field to influence tissue fluids, thus increasing the flow exchange rate, blood circulation, the phagocytic ability of white blood cells, the rate of tissue repair, reducing the tension in muscles and connective tissues surrounding the knee joint . The traction could immobilize and rest the affected limb, and also utilize the creep properties of viscoelastic bodies (such as ligaments and muscles), releasing the spasm of muscles surrounding the knee joint, increasing joint space, reducing intra-joint pressure, increasing the range of joint motion, adjusting the line of biomechanical force of the joint . Thus, pain was reduced, and knee joint functions and physiological conditions of the soft tissues were improved.
This study has several limitations. First, this was a single-center study with a small sample size. Second, this is a one-arm study with no control group. Third, the follow-up time of this study was relatively short. Future multicenter randomized control trials with larger sample sizes and longer follow-up durations can help verify the findings of the present study.
Therefore, the effectiveness of deep thermotherapy combined with dynamic traction is evident in treating KOA. High-frequency ultrasound has evident advantages in evaluating the treatment outcomes, and joint effusion, thickness of synovium, and blood flow signal in synovium could be indicators for accurate evaluation.