1. Introduction
Chronic Low Back Pain (CLBP) is one of the most common musculoskeletal disorders worldwide [1]. The disease is characterized by localized pain below the costal margin and above the inferior gluteal folds [2]. Chronic pain may persist in 10% to 20% of CLBP patients after medical and surgical treatment [3]. Unfortunately, the experience of pain is often accompanied by physical, psychological, social, and financial problems. Chronic pain is a leading cause of long-term disability worldwide [4]. It can have far-reaching consequences, such as psychological distress (e.g. depression, anxiety, and hopelessness), increased rates of pain-related disability, pain-related changes in cognition, and decreased quality of life [5]. These studies suggest that chronic conditions affect the quality of life in this group of patients. Besides attention to the morphological basis, biopsychosocial interventions should be administered to improve quality of life and adaptation to chronic illness [6, 7].
Incorporating psychological interventions into multidisciplinary approaches is beneficial for the treatment of CLBP. Psychological interventions can directly increase self-management knowledge and cope with stress, improve coping skills and emotion regulation, and facilitate adaptation to chronic ailments in people with CLBP [5]. Psychological interventions also increase patients’ active participation, which reduces the rate of symptom recurrence and healthcare costs [8]. Previous research studies have shown that interventions such as Cognitive-Behavioral Therapy (CBT) [9, 10, 11, 12] and other combination approaches with mindfulness [13, 14, 15, 16, 17] are highly effective in improving the physical and psychological symptoms of people with CLBP. Moreover, review studies have shown that psychological interventions significantly reduce anxiety, pain, and depression [18] and improve the quality of life [19] and general functioning [20] in people with CLBP.
In the literature review, many experimental studies have examined different psychological interventions to reduce pain symptoms and improve the psychological status and quality of life of these patients. Accordingly, it is necessary to review the literature, identify the most effective treatment models based on the best research designs and use them in Iranian research. This study aimed to review the effectiveness of all psychological interventions in improving the psychological status of people with CLBP and provide recommendations for future therapeutic interventions.

2. Methods and Materials/Patients
This study was conducted using a systematic review method in published studies from January 2010 to December 2020. Indexing databases such as Magiran, PubMed, Scopus, and Google Scholar were examined. To search for articles, we used the key terms of “psychology”, “intervention”, “low back pain”, “chronic illness”, “quality of life”, “empowerment”, “psychotherapy”, “psychological interventions”, “clinical trials”, and “randomized clinical trial”. In the PubMed database, the search was done based on the Medical Subject Heading (MeSH) keywords of “low back pain” by applying filters (All time from 2010 to 2020, Title/Abstract and Clinical Trial article type). Finally, a total of 857 articles were identified from this database. This search strategy was limited to Iran affiliation that only resulted in 75 articles. In other databases, an advanced search was performed based on the keyword “low back pain” and in combination with other keywords mentioned.
To thoroughly search the keywords, we used each keyword in combination with “low back pain”. As a result, 1740 articles were found with the searched keywords in their titles or content. Two researchers reviewed the titles of the articles and the abstracts; then, many articles were removed from the review due to duplication, irrelevance, and lack of inclusion criteria. 
Cohen’s kappa coefficient was also calculated as optimal (κ=0.45). Finally, 14 articles were selected and reviewed. Figure 1 shows the steps for reviewing the resources.

The inclusion criteria for articles were as follows: published in a specific period, written in Persian or English, and conducted on patients with low back pain. Qualitative and single case articles, case reports, and articles based on pharmacological and medical interventions were excluded. To review the articles, we used the standard critique framework for health articles [21] and Sidant and Braden’s approach for evaluating behavioral interventions [22]. To systematically review the articles, we considered the indicators of authors’ last name and year of publication, type of intervention or theoretical framework, country of research, number of participants in the research, method of intervention, and outcome.

3. Results
In this study, 14 studies were reviewed, 7 of which were conducted in Iran. According to the results of Table 1, the studies conducted in Iran were based on the theoretical framework of Cognitive-Behavioral Therapy (CBT) alone [9, 10, 11], CBT combined with mindfulness [15, 16, 17], and Acceptance and Commitment Therapy (ACT) [23].

The sample size in Iranian studies for intervention groups varied from 10 [15, 23] to 39 [16]. The studies mainly were quasi-experimental [9, 10, 11, 17, 23]; some were experimental [16], and only one study had a follow-up [17]. Moreover, psychological and physical outcomes such as reduction and severity of pain were considered in the Iranian studies. According to the results of Table 2, studies performed outside Iran, like those conducted in Iran, are mainly based on the theoretical framework of CBT [12, 24, 25, 26] or its combination with mindfulness and meditation [13, 14, 25, 27].

The sample size in non-Iranian studies ranged from 16 [27] to 464 [12]. The foreign studies were based on a randomized clinical trial design, except for one study [27], which had a single-group design. A significant point in the non-Iranian researches was follow-up testing from one month [13] to 13 months [25].

4. Discussion
This study aimed to review the role of psychological interventions in people with Chronic Low Back Pain (CLBP). The results of our study showed that psychological interventions affect a wide range of psychological and pain-related outcomes. Cognitive-Behavioral Therapy (CBT) intervention is one of the most widely used interventions for CLBP, which effectively affects positive emotions, psychological well-being, and pain perception [9]. It improves self-efficacy and quality of life [10], reduces psychological distress (e.g. anxiety, depression, and stress) [11], pain perception and intensity [25], and depressive and anxiety symptoms [26].
By learning cognitive reappraisal and emotion regulation, the intervention groups could generate positive emotions and modulate negative emotions, which directly contributed to reducing their psychological distress [28]. Learning the main components of this treatment (e.g. imagination, exposure, and cognitive restructuring) are also essential factors in reducing stress and anxiety. In addition to these components, cognitive restructuring training can affect patients’ perception of pain and reduce their helplessness [25].
In recent years, the dominance of third-wave behavioral therapy has been observed in research on the health and empowerment of chronically ill patients. Meanwhile, the focus on mindfulness and the application of meditation and relaxation techniques through the combination of CBT has led to the formation of new treatment models such as Mindfulness-Based Stress Reduction (MBSR) and Mindfulness-Based Cognitive Therapy (MBST) [29, 30]. Stand-alone therapies such as Acceptance and Commitment Therapy (ACT) have also been welcomed by researchers in the field of chronic pain [31]. Our study has shown that these therapies are effective in reducing pain perception, stress, anxiety, and depression [13, 15, 17], improving quality of life [16, 23, 26], physical function and pain reduction [14], and pain relief [25].
Mindfulness is the common denominator of several complementary therapies that have originated in the Buddhist spiritual tradition and are integrated into behavioral therapy approaches [32]. Mindfulness is a state of consciousness described as momentary awareness without judgment and is a way to accept and trust personal experiences [33]. Therefore, mindfulness-based therapies involve training to maintain mindfulness during routine activities in daily life and an acceptance of personal moods and emotions without judgment [34]. Because CLBP patients in these therapies can accept their negative emotions related to pain without judgment, this treatment can effectively reduce patients’ psychological symptoms and pain perception.
In reviewing the selected research, some points can be considered that may help improve the quality of future studies. The main criticisms are related to studies conducted in Iran. All of them were conducted using quasi-experimental and experimental methods without considering randomization and blinding. In other words, no research was found in this field based on RCT design [9, 10, 11, 15, 17, 23]. Also, in the studies conducted in Iran, except for one study [9], no follow-up test was conducted. Using the RCT research design and conducting follow-up tests after one [13] to 13 months [25] emphasizes the value of research conducted abroad and provides more reliable results. Our suggestion for future studies in Iran is to take an effective step to promote clinical research by developing the RCT design and conducting follow-up tests. In most studies conducted in Iran and abroad, confounding variables such as age, gender, drug use, and history of spinal surgery have not been reported, which makes the generalization of the results difficult.

5. Conclusion
Our studies showed that CBT combination therapy with mindfulness played an influential role in improving psychological symptoms, quality of life, and reducing pain perception in CLBP patients. Given that the physical and psychological consequences of CLBP are highly correlated, it is suggested that psychological interventions be used in addition to physical interventions and surgeries to reduce the severity and perception of pain and psychological symptoms such as anxiety and depression.


Ethical Considerations
Compliance with ethical guidelines
There is no animal or human research reported in this study so there was no need for ethics board approval.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
All authors contributed equally to performing the project and preparing the manuscript.

Conflict of interest
There is no conflict of interest concerning this study.


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