1.    Introduction
The most prevalent form of arthritis and joint disease in humans, osteoarthritis (OA), also known as degenerative joint disease (DJD), can cause the patient to experience severe disability and chronic pain (1). The knee joint is the largest joint in the body and has a complex structure due to the variety of functions it performs. Due to mechanical stress, this joint is vulnerable to traumatic and destructive injuries. Since the knee joint is not covered by fat or muscle layers and is at the end of the two long arms of the tibia and femur lever, both environmental and anatomical factors play a role in the frequency of injuries (8). As there is no standard, effective treatment for osteoarthritis, and treatments can include drugs, non-drugs, or surgery. In this regard, exercise therapy is used as the primary osteoarthritis intervention because it has been demonstrated to effectively reduce pain and restrict activity in this condition (9). Pain is one of the signs of osteoarthritis of the knee, which depends on activity in the early stages, worsens during activity, and gets better with rest (10). A balance disorder that increases the risk of falling is one of the significant complications experienced by elderly people with knee osteoarthritis. Exercise therapy is a different approach. It has been reported that individuals with knee osteoarthritis exhibit quadriceps muscle weakness in addition to a pronounced decline in proprioception. Knee osteoarthritis can both cause and result in weak quadriceps muscles and a decreased sense of proprioception. Since these two factors are among the most crucial in regulating balance, people with knee osteoarthritis have weak static balance and develop dynamic balance (13). Among the various approaches to managing osteoarthritis, physiotherapy is a course of care that lessens discomfort, improves muscle strength, and extends joint range of motion. It is crucial in the management of moderate to severe osteoarthritis. Therefore, the aim of this study is to investigate the effect of electrotherapy and exercise therapy on pain and balance in women with knee osteoarthritis.
2.    Methods
The pre-test-post-test research design was used in the current semi-experimental applied research methodology. In the physiotherapy clinic of Ardabil, the statistical population consisted of middle-aged women who had osteoarthritis in their knees. Middle-aged individuals between the ages of 45 and 65 randomly chosen from the statistical population of 30 individuals and divided into three groups.
The entry requirements for the study were knee pain for at least three months and an average pain level of more than three units (on a VAS scale) while the exclusion requirements were knee surgery, a history of neurological diseases, an intra-articular corticosteroid injection within the previous six months, and the presence of knee surgery. In the previous six months, the company had taken part in physical therapy training programs.
First, the procedures and protocols for the study were explained to the participants. Participants completed the screening process for inclusion and exclusion criteria, and then they were asked questions regarding their age, gender, weight, exercise habits, medication use, and medical history. The VAS scale, which typically consists of a ten-centimeter line on which the patient marks a point in accordance with his feelings regarding his present situation, was used to assess the pain. An American-made Niro Bartek power plate with a sampling rate of 1000 Hz was used to verify the balance. These individuals' balance was improved through the Romberg exercise (16). For the electrotherapy program, all subjects were treated with a TENS machine from Germany for twenty minutes prior to the start of the exercises and a new ultrasound machine from Germany continuously for six times at a frequency of 3 MHz and an intensity of 1.2 watts per square centimeter. A physiotherapist applied their techniques near the knee joint. Three sessions per week for eight weeks were dedicated to the exercise.
3.    Results
The results of the experiment and statistical analyses of variance of repeated measures used to compare pre-test and post-test pain showed that the effect of time factor in the pain test was statistically significant (p=0.048; d=0.278). Additionally, pairwise comparisons revealed that the electrotherapy group's post-test result was 37.99% lower than its pre-test result (Table 1).

As previously mentioned, the displacement of the center of pressure in two anterior-posterior and internal and external directions during the stance phase has been obtained through the force plane in order to obtain the dynamic balance of the subjects while walking. The findings presented in Table 5 demonstrated that the group factor's impact on the values of COPx was statistically significant (P=0.019; d=0.180). Comparing training and control group using pairwise comparisons revealed that the range of COPx values was narrower in the training group. Additionally, the group factor had a statistically significant impact on COPy values (P=0.034; d=0.151). In comparison to the control group, the trained group's COPy values were lower (Table 2).

4.    Conclusion
The current study's findings revealed that there were no significant differences in the effectiveness of electrotherapy treatment in reducing pain and enhancing balance in elderly women with osteoarthritis, and that both exercise groups experienced improvements in both areas. In this regard, Long et al. (2008) in a study titled "Strength exercises for the treatment of knee arthritis: a systematic review" came to the conclusion that fifty to seventy percent of patients with osteoarthritis benefit from resistance exercises in terms of reduced pain and improved performance (17). According to Bhatti et al.'s research published in "Effect of Physiotherapy Treatment in Knee Osteoarthritis: An Evidence-Based Study" (2019), combining knee exercises with pain-relieving physiotherapy techniques is more advantageous than using just one technique (18). A study by Shamsi et al. (2020) titled "Effectiveness of Physiotherapy Management in Knee Osteoarthritis: A Systematic Review" demonstrated that physiotherapy treatment is an efficient way to lessen knee OA patients' pain without causing any negative side effects. Quadriceps muscle activation is improved by electrotherapy methods in combination with therapeutic exercise programs designed to treat knee OA patients. This is done by reducing pain and improving performance during exercise.
The use of traditional restrooms after menopause, bad habits like sitting on the floor, and obesity are all significant and widespread contributors to osteoarthritis of the knee joint, according to the findings of the current study. More research should be done on these factors, which include underlying illnesses, trauma, intense exercise, genetics, and poor nutrition. These factors may also contribute to the development of this disease. Therefore, it is possible to reduce excess body weight before middle age and engage in disease-related exercise to reduce the incidence or severity of this disease.

Ethical Considerations
Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
All authors equally contributed to preparing article.
Conflicts of interest
The authors declared no conflict of interest.