The effectiveness of ESWT on pain, function and mental health of patients with CLBP was systematically reviewed. The results of this meta-analysis showed that ESWT, either as stand-alone or adjuvant treatment for CLBP, significantly reduced VAS scores at week 4 and week 12 compared to the control group, with a “moderate” recommended level based on GRADE [26]. Further, “low-to-moderate” quality evidence showed significant improvement in ODI scores at week 4 and week 12 for ESWT compared to other conservative treatments. However, with regard to mental health scores at week 4, we did not find significant differences between the two groups. Due to the limited number of articles included, further randomized controlled trials are needed to investigate the effectiveness of ESWT. In addition, no ESWT-related adverse events were found (not recorded or did not occur) in any of the 12 RCTs included in the study.
According to our information, there was only one previous meta-analysis about the application of ESWT in CLBP, but we found that this study had high heterogeneity in both pain and dysfunction index analyses, and no subgroup analysis or sensitivity analysis was conducted [27]. In addition, we found that this previous meta-analysis included an unpublished master's thesis and a study of participants with postpartum low back pain that may have affected the reliability of the results and were excluded from our study. Finally, we included 12 RCTs with a total of 632 patients, and explored the sources of the associated heterogeneity. Moreover, studies have shown that the occurrence of chronic low back pain is rarely caused by a single factor, but by a variety of physical and psychological mechanisms [28]. Holmes [29] believed that the limitations or disabilities in patients' daily life would lead to some psychosocial problems, which would further damage their quality of life. Therefore, we conducted the first meta-analysis about mental health scores in CLBP patients.
Low back pain is one of the most common conditions in clinical practice, with pain and movement limitation being the most basic symptoms. Pain alters the contraction pattern of the trunk muscles, resulting in spasm, increased tone and even atrophy of the low back muscles, significantly reducing the ability of the muscles to engage and destabilising the spine and vertebral balance [30, 31]. In addition, prolonged poor posture in the low back can lead to fatigue of the low back muscles and oedema of the surrounding soft tissues, exudation of inflammatory cells, accumulation of metabolic products and degeneration of muscle fibres, resulting in local adhesions, chronic hypoxia of the muscles and pain, all of which can contribute to recurrent episodes of CLBP [32, 33].
CLBP is treated with a variety of clinical approaches, including conservative treatment and surgical treatment. In its initial clinical use, ESWT was used by German medical scientists to save patients from surgical pain treatment [34]. With the passage of time, ESWT technology is gradually mature, and its clinical application is also increasing. Many clinical trials have shown that ESWT treatment can significantly reduce pain and complications of patients with CLBP [14, 22]. ESWT mainly treats chronic low back pain through the direct mechanical action of shock wave, and indirectly causes mechanical action through cavitation [35]. Firstly, when shock wave enters the human body, different mechanical effects will be generated at the interface of different tissues due to different contact media such as fat, tendon, ligament and bone tissue, and finally different forces will be generated on cells [36]. In these forces, tensile stress can relax tissues. It promotes microcirculation, while compressive stress can change the elasticity of cells and increase their ability to absorb oxygen for therapeutic purposes [37, 38]. Secondly, ESWT causes a large number of tiny bubbles to be created in the tissue, which rapidly expand and burst under the action of the shock wave, producing a high speed fluid microjet and a shock effect [39]. This cavitation effect is particularly effective in reopening occluded microvasculature and releasing soft tissue adhesions at the joint. The exact mechanism of the pain-relieving and functional properties of ESWT is not fully understood, and several studies have attempted to elucidate the mechanisms of shock waves from basic science and clinical studies. Studies have shown that the energy released by ESWT is well able to stimulate pain receptors located in skin, muscle, connective tissue, bone and joints, and activate unmyelinated C and A delta fibers to initiate the "gated" pain control system and block nerve transmission, resulting in analgesic effects [40, 41]. In addition, ESWT has been shown to significantly downregulate the levels of IL-1, TNF-α and MMPs in degenerated joint tissues, thereby reducing the local inflammatory response [42, 43]; At the same time, it also promotes the secretion of pain-reducing chemicals (e.g. endorphins), inhibits the release of pain factors such as substance P and calcitonin gene-related peptides, reduces peripheral nerve sensitivity and increases pain threshold levels [44, 45].
It is well known that adverse reactions are a major concern when evaluating the efficacy of ESWT. Therefore, the higher the risk of adverse reactions, the lower the clinical value of ESWT. In our study, 12 RCT articles all reported the incidence of adverse reactions after ESWT treatment. Therefore, based on the current meta-analysis, ESWT did not increase the risk of local reactions. However, considering the small sample size included in the study, the safety of ESWT needs to be further discussed.
Some limitations of this study should be noted. First, there are differences in etiology, pain duration, and related parameters used by ESWT in each study, which may lead to heterogeneity in the combination of results and limited evidence. Second, there are inevitably heterogeneous factors among the included researchers, such as age, gender, and racial differences. Next, different biases, including selection bias, language bias, data provision bias and publication bias, may reduce the accuracy of the results. Last but not least, the pain, function and mental health scores included in this meta-analysis were all obtained through questionnaires, and the outcome indicators may be subjective. If there are enough articles with objective observation indicators in the future, relevant studies can be improved.