Introduction
Knee osteoarthritis is a disease with gradual loss of knee joint cartilage and related secondary changes of knee joint structure. It is more common in elderly individuals, those with injuries, obesity, and women. Typical symptoms include pain, swelling, flexion limitation, joint deformation, and increased pain after activity, especially when climbing the stairs or slopes. It reduces walking distance and interferes with physical activity, which lowers the quality of life of the affected elderly population, and causes financial and social problems such as increased medical costs and loss of productivity [
1].
Knee osteoarthritis is treated with anti-inflammatory drugs and intra-articular steroid injections. These treatments are effective in relieving pain and improving motion performance, but have adverse effects on the digestion, urinary, and cardiovascular systems when used over a long period of time. Even replacement surgery (a structural treatment) is not a permanent treatment and further surgery is required when the replacement wears out [
2].
Moxibustion is a representative traditional Korean medicine treatment widely used to relieve the symptoms of knee osteoarthritis. A meta-analysis of large-scale clinical studies showed that moxibustion is effective in treating knee osteoarthritis [
3-
5]. However, despite the effectiveness of moxibustion, harmful gases generated during the combustion process, and difficulties in precise temperature control may cause adverse effects such as burns and respiratory discomfort. In a study analyzing the adverse effects of moxibustion, the most frequent adverse effects were allergic reactions, burns, and infection [
6].
Despite the effectiveness of moxibustion, its clinical use is limited due to adverse effects, and the type of moxibustion performed; laser moxibustion, smokeless moxibustion, and electronic moxibustion are being developed as alternatives [
7-
9]. In particular, electronic moxibustion has the advantage of being able to control and maintain the temperature, and it does not generate harmful gases in the process; therefore, the risk of burns and secondary risks caused by inhalation of harmful gases are relatively low.
Although the use of electronic moxibustion for the treatment of knee osteoarthritis is increasing in clinical practice, the safety of electronic moxibustion has not been seriously considered. The purpose of this study was to assess the safety of electronic moxibustion treatment for knee osteoarthritis patients by retrospectively studying case reports reporting 2nd degree burns and performing a literature review of clinical studies reporting adverse events.
Discussion
In the 3 cases retrospectively reviewed, all patients experienced superficial 2nd degree burns with redness, blister formation, and tingling after 10 minutes of electronic moxibustion at 45°C. Although all patients received the same intervention, each patient had different symptoms and time of occurrence. Medical tape was used to attach electronic moxibustion to the skin surface, and the treatment was performed once a day during the hospitalization period.
In the literature review, adverse events were reported in 4 studies (8 of 167 patients; 4.79%), and 1 study did not report this information. There were no cases of burns with blisters, but redness, a tingling sensation, itching, crust formation, and pain were reported.
The relationship between moxibustion temperature and burns has been widely researched to determine safety. In an vivo model, burns occurred on the skin of the back of the rat in 4 minutes when electronic moxibustion was performed at 47°C, and burn occurred within 1 minute when the device was set at 49°C [
15]. Another study reported that if the temperature of electronic moxibustion was rapidly increased to its maximum within 1 minute, erythema may persist at the application site beyond 24 hours [
7]. A heating temperature of ≥ 42°C was reported to be clinically significant, and can have a positive effect on C-fiber receptor activity at ≥ 44.5°C [
7]. The maximum temperature of electronic moxibustion currently accepted in Korea is in the range of 41-47°C, and 2 consecutive treatments are prohibited on the same area of skin. In addition, electronic moxibustion with a maximum temperature of ≥ 45°C has been prohibited because of concerns regarding burns on the head and face. Despite electronic moxibustion being performed according to the guidelines, burns occurred in the 3 retrospective cases reviewed. Other factors involved in causing burns during electronic moxibustion need to be considered.
The extent of skin damage from a thermal contact burn is determined by the total thermal energy delivered to the skin and the skin thickness. The amount of transferred thermal energy is affected by the temperature, duration, contact area, and heat capacity of the contact material [
16,
17]. Studies on the factors except for the temperature and duration of treatment time, involved in the extent of skin damage caused by a thermal contact burn have rarely been researched. It is possible that the occurrence of burns may depend on the patient’s age and underlying conditions/diseases. A literature review of 64 moxibustion case reports reported that there was no difference in the incidence of adverse effects according to age, but it is difficult to generalize these results due to the small number of patients analyzed [
18].
In the literature review performed for this current study, 2 studies where higher temperatures and longer duration times of electronic moxibustion treatment were used no adverse events were reported [
11,
12]. In 2 other studies that did report adverse events, burns more severe than 2
nd degree burns were not mentioned. It is difficult to determine which factors are associated with preventing burns during electronic moxibustion treatment. However, in the studies by Tang and Xue [
11,
12], wormwood oil was applied before the attachment of electronic moxibustion device. It is necessary to consider whether the application of oil could prevent burns.
In a study by Kang et al [
10] using the same brand of electronic moxibustion device as used in the 3 case reports retrospectively reviewed, similar adverse events such as redness and crust formation occurred, and in the study by Xue et al [
11], Tang et al [
12], and Lu et al [
14] using the same device which was set at 46-50°C, no adverse events were reported. This implies the possibility of differences in contact material, contact area, and the rate of temperature change of the device.
There were also differences in the method of attaching electronic moxibustion to the knee joint, including medical tape, brace, and strap. This suggests that the effect on the skin according to the fixation method needs to be considered. In the case of tape, it is also necessary to determine the chemical components within the tape which may affect the skin during thermal stimulation.
In the reporting process of adverse events within clinical studies, the time point when adverse events were collected, and the investigation procedure to inform patients to report adverse effects should be in advance of treatment and is very important. The 2 studies reporting no adverse events did not mention the time point of measurement, and consequently, there may be a possibility of reporting bias.
It has been reported that patients in Eastern Asia tolerate burns caused by moxibustion because of the symptom relief the treatment provides [
19]. The possibility of unreported adverse events due to concerns about discontinuation of treatment should also be considered.
This current study has the following limitations. Firstly, it was difficult to determine the proportion of burns after electronic moxibustion treatment because the clinical charts in this hospital only report 2nd degree burns or more severe burns. Secondly, the exact cause of a burn that occurred after electronic moxibustion treatment could not be identif ied. However, the factors to be considered were summarized but further research is necessary.
This study is worthwhile as it is the 1st study to focus on superficial 2nd degree burns caused by electronic moxibustion treatment for knee osteoarthritis in clinical practice. Various factors except for the moxibustion temperature and duration of time, are involved in burns occurring. To prevent these burns, if the minimum temperature and treatment time required for moxibustion are not applied, this treatment may not be effective. Besides decreasing the temperature of electronic moxibustion, studies on the heating source, and contact surfaces with the skin should be studied in the future. Electronic moxibustion should be developed and improved as a safe effective treatment to replace existing moxibustion treatment.