# Transcranial Direct Current Stimulation in the Treatment of Chronic Knee Pain: A Scoping Review
## 4 Discussion  
Transcranial Direct Current Stimulation (tDCS) has emerged as a potential non-invasive neuromodulatory technique for chronic pain management, offering an alternative to conventional therapies. The surge in research focusing on its application for knee osteoarthritis in elderly individuals has yielded a spectrum of results, ranging from promising to inconclusive. This review synthesizes findings from 11 pivotal studies, providing a comprehensive overview of the multifaceted landscape of tDCS research [30, 33, 34]. Initial studies, such as those by [PERSON] et al., 2018 [16] and [PERSON] et al., 2020 [18], have demonstrated tDCS's potential as an alternative or complementary treatment for knee osteoarthritis pain. Their rigorous methodologies and significant outcomes in pain measures have strengthened the case for tDCS. Particularly noteworthy are the advancements in neuroimaging, especially studies employing functional near-infrared spectroscopy (fNIRS). The study by [PERSON] et al., 2020 [18] is exemplary in this context, providing compelling evidence of the neuromodulatory effects of tDCS through fNIRS. These studies offer valuable insights into the brain's response to tDCS, revealing alterations in cortical hemodynamics and connectivity patterns associated with pain perception. Such neuroimaging findings are crucial, as they lend physiological credibility to the subjective pain relief reported by patients, thereby bridging the gap between subjective experiences and objective measures. The study by [PERSON] et al., 2020 [27] further complements this narrative by demonstrating reductions in inflammatory markers, suggesting a potential physiological basis for the analgesic effects of tDCS. Nevertheless, the study by [PERSON] et al., 2021 [30] highlights the complexities involved, raising pertinent questions about the placebo effect and the genuine efficacy of tDCS. The heterogeneity in study designs, population sizes, and treatment protocols poses significant challenges in synthesizing these findings. This variability, particularly in treatment duration and intensity, complicates the interpretation of results. One of the key strengths of this review is its comprehensive scope, covering a wide range of studies and providing a holistic view of the current state of research on tDCS for knee osteoarthritis in elderly individuals. Many included studies employed rigorous methodologies, such as randomized controlled trials, enhancing the reliability of their findings. Additionally, the review includes studies utilizing different tDCS protocols, offering insights into various effective approaches. Furthermore, some studies, like that by [PERSON] et al., 2020 [27], extend beyond subjective measures to include objective markers such as inflammatory cytokines, adding depth to the understanding of tDCS effects. The review focuses on a prevalent condition that is often inadequately managed, making the findings highly relevant to both clinicians and patients [18, 31]. Despite these strengths, the review also has several limitations. The diversity in methodologies, while a strength in some respects, also makes it challenging to draw overarching conclusions. Some studies had relatively small sample sizes, limiting the generalizability of the findings. Most studies had short follow-up periods, making it difficult to assess the long-term efficacy and safety of tDCS. The lack of standardized protocols for tDCS application complicates the comparison of results across studies. The presence of studies with no significant differences between active and sham tDCS raises questions about placebo effects and the actual efficacy of the treatment. Few studies comprehensively addressed the potential adverse effects of tDCS, leaving gaps in understanding its safety profile [20, 29]. In light of these findings, it is evident that while tDCS holds promise, there is a pressing need for more standardized and extensive research.