Cupping therapy and chronic back pain: systematic review and meta-analysis

ABSTRACT Objectives: to evaluate the evidence from the literature regarding the effects of cupping therapy on chronic back pain in adults, the most used outcomes to evaluate this condition, the protocol used to apply the intervention and to investigate the effectiveness of cupping therapy on the intensity of chronic back pain. Method: systematic review and meta-analysis carried out by two independent researchers in national and international databases. Reference lists of systematic reviews were also explored. The quality of evidence was assessed according to the Jadad scale. Results: 611 studies were identified, of which 16 were included in the qualitative analysis and 10 in the quantitative analysis. Cupping therapy has shown positive results on chronic back pain. There is no standardization in the treatment protocol. The main assessed outcomes were pain intensity, physical incapacity, quality of life and nociceptive threshold before the mechanical stimulus. There was a significant reduction in the pain intensity score through the use of cupping therapy (p = 0.001). Conclusion: cupping therapy is a promising method for the treatment of chronic back pain in adults. There is the need to establish standardized application protocols for this intervention.


Introduction
Chronic back pain causes physical, emotional and socioeconomic changes (1)(2)(3) and, consequently, high use of medicines and health resources (4) . The search for demedicalization leads to an increasing use of integrative and complementary practices, such as Traditional Chinese Medicine (TCM) resources, to complement pain-related allopathic care (5) . Cupping therapy is one of the recommended TCM therapies for chronic pain reduction (6) . It involves the application of cups of different materials (7) in an acupoint or area of pain by means of heat or vacuum apparatus (8) .
The effect on pain reduction has not yet been fully elucidated (9) , but different mechanisms of action, based on several assumptions (10) , are attributed to cupping therapy, such as the metabolic, neuronal hypotheses (9,11) and TCM (12) . Evidence of the efficacy of this intervention is limited because of the lack of high quality, well-delineated randomized controlled trials (RCTs) (6) that result in validated and efficient protocols for the treatment of chronic back pain. Therefore, this study aims to evaluate the literature evidence regarding the effects of cupping therapy on chronic back pain in adults compared to sham, active treatment, waiting list, standard medical treatment or no treatment, outcomes most commonly used to assess this condition, the protocol used to apply the intervention and subsequently investigate the effectiveness of cupping therapy on the intensity of chronic back pain.

Method
A systematic review of the literature was performed, followed by meta-analysis, used to determine the intensity of back pain in adult clients. The study was based on the criteria of the Preferred Reporting Items for Systematic Reviews and Meta-Analyzes (PRISMA Statement) (13) . The terms, controlled and free, were combined by means of the Boolean operators OR and AND as follows: ("Back Pain" OR "Low Back Pain" OR "Sciatica" OR "Chronic Pain" OR "Musculoskeletal Pain" OR Myalgia OR "Neck Pain" OR "Low Back Pains" OR "Musculoskeletal Pains" OR "Muscle Pain" OR "Neck Pains" OR "Cervical Pain" OR "Cervical Pains" OR Lumbago OR "lumbar pain") AND ("cupping therapy" OR cupping OR cups).
The eligibility criteria for the selection of articles were: RCT with adults (18 years or older); chronic pain (for three months or more) (15) in at least one of the segments of the spine (cervical, thoracic and/or lumbar); use of cupping therapy (dry, wet, massage, flash) (7) compared to one or more of the following groups: sham, active treatment, waiting list, standard medical treatment, or no treatment.
We excluded studies that did not present online abstract in full for analysis, those that were not located by any means and studies with pregnant women.
In order to collect the information from the selected studies, we used an adapted form (16) in accordance with the recommendations of the Revised Standards for Reporting Interventions in Clinical Trials of Acupuncture (STRICTA) (17) and the classifications of cupping therapy (7,18) .
The following data were extracted: article identification (title, author (s)/training area, journal, year of publication, study country/language); objectives; methodological characteristics (design, sample size and loss of follow-up; inclusion and exclusion criteria); clinical data (number of patients by sex, mean age, diagnosis, duration of symptoms); description of interventions in the follow-up groups (number of sessions, duration of treatment, type of technique applied (dry, wet, flash or massage cupping), application device, time of stay of the device, suction method (manual, fire, automatic-electric)/suction strength (light, medium, strong or pulsating) (18) ; peculiarities of the intervention; application points; training area of the professional who carried out the intervention; years of experience in the area); outcomes and methods of evaluation (number of evaluations, intervals between them, measurement tools); data analysis; main results; and study findings.
The methodological quality of eligible studies was assessed using the Jadad scale (19) , which is centered on internal validity. The questions have a yes/no answer option with a total score of five points: three times one point for the yes responses and two additional points for appropriate randomization and concealment of allocation Moura CC, Chaves ECL, Cardoso ACLR, Nogueira DA, Corrêa HP, Chianca TCM. methods. Two independent reviewers conducted the evaluation, and a third investigator was consulted to solve possible disagreements.
Data analyzes were performed using Stata SE/12.0 statistical software. The absolute difference between means with 95% confidence intervals was selected to describe the mean differences between the treated and control groups in the evaluation performed shortly after treatment. P-value <0.05 was considered as statistically significant. Potential heterogeneity among the studies was examined using Cochran Q (20) and I 2(21) statistics.
Since there was statistical significance in the test for heterogeneity of the results (p <0.05) and the calculated value of I 2 suggested a moderate to high heterogeneity (67.7%) (21) , the random effects model was adopted for the analysis.

Results
A total of 614 studies were found in electronic and manual searches. Of these, 296 were removed from the list because they were duplicates. After reviewing titles and abstracts, 265 studies were excluded and 53 remained for analysis of the full text. Of these, 11 studies were not found (online, via bibliographic switching or direct contact with authors) and 26 articles were excluded. Finally, 16 articles remained in the review for the synthesis of the qualitative analysis and 10 articles entered the quantitative analysis ( Figure 1).   (23) To test the effectiveness of Cupping Massage in patients with neck pain.
Cupping massage (n*=25) Waiting list (patients were asked to continue medical care, but refrain from invasive treatments, such as injections or acupuncture) (n*=25) Cupping massage appears to be effective in reducing pain and increasing function and quality of life in patients with chronic nonspecific cervical pain. Cupping therapy (n*=50) Acupressure (n*=50) Control group without intervention (n*=50) Although pain intensity decreased in both groups, this reduction was significant in the cupping therapy group. Therefore, both cupping therapy and acupressure may be effective in reducing postpartum low back pain in primiparous women.
Chi LM et al. To investigate the efficacy of cupping therapy in relieving chronic neck and shoulder pain among community residents and changes in skin surface temperature.
Cupping therapy (n*=30) Control group without intervention (n*=30) Cupping therapy increased the surface temperature of the skin and reduced systemic blood pressure. The subjective experience of pain intensity also reduced. Cupping therapy resembles an analgesic effect that has no known negative side effects and can be considered safe.
AlBedah A et al.
(2015) (36) To assess the effectiveness and safety of Wet Cupping as a treatment for persistent and nonspecific low back pain.
Wet cupping and analgesic drug (maximum of three 500mg acetaminophen tablets per day) (n*=40) Analgesic drug (maximum of three 500mg acetaminophen tablets milligrams per day) (n*=40) Wet cupping works to reduce pain and improve disability associated with nonspecific and persistent low back pain for at least 2 weeks after the end of the intervention.
Emerich M et al.
(2014) (9) To measure, in parallel, the metabolic changes in the tissue under the glass cups and the pressure pain threshold.

Dry cupping (n*=12)
Comparison between the side on which cupping therapy was performed with the contralateral side, which did not receive the intervention (n*=12) Cupping therapy promotes anaerobic metabolism lasting 280 minutes in the subcutaneous tissue and increases the immediate pressure pain thresholds in some areas. Lauche R et al.
(2013) (24) To test the effectiveness of 12 weeks of Cupping Massage performed at home, compared to the same period of progressive muscle relaxation in patients with chronic nonspecific neck pain.

Cupping massage (n*=30)
Instructions and training to perform progressive muscle relaxation at home twice a week, 20 minutes per session, and to record this practice in a journal (n*=31) Cupping massage is no more effective than progressive muscle relaxation in reducing chronic nonspecific neck pain. Both therapies can be easily used at home and can reduce pain to a clinically relevant minimum extent. However, cupping massage is better than progressive muscle relaxation in improving well-being and decreasing sensitivity to pressure pain.
Kim TH et al.
(2012) (34) To compare the effects of cupping therapy and the "heated pad" on neck pain, functional disability and quality of life in video display terminal workers.
Cupping therapy (n*=20) Heated hot water pads applied to the neck and upper trapezius muscle for 10 minutes, 3 times a week, for 2 weeks (n*=20) 2 weeks of cupping therapy associated with an exercise program may be effective in reducing pain and improving neck function in workers at Video Display Terminal.
(the Figure 2  To test the efficacy of a single traditional cupping therapy treatment in patients with chronic nonspecific chronic neck pain. Cupping therapy and non-steroid medication for pain and physical therapy (n*=22) Non-steroid medication for pain and physical therapy (in both groups) (n*=23) A single application of cupping therapy may be effective in the treatment of chronic nonspecific cervical pain.
Lin ML et al.
(2012) (30) To evaluate the effect of laser acupuncture and soft cupping on low back pain.
Laser acupuncture and soft cupping (n*=28) Soft cupping and laser without radiation (n*=29) Laser acupuncture and mild cupping therapy may be a suitable treatment for patients with low back pain.
Cramer H et al.
To compare the effects of a series of 5 sessions of Pulsating Cupping with standard medical care in relieving chronic nonspecific cervical pain.
Pulsating Cupping (n*=24) Self-directed standard medical care (physical therapy, exercises and analgesic drugs as needed) (n*=24) Pneumatic pulsation therapy appears to be a safe and effective method to relieve pain and improve function and quality of life in patients with chronic neck pain.
Kim JI et al.
(2011) (35) To determine the efficacy and safety of Wet Cupping treatment for persistent nonspecific low back pain.
Wet-cupping (n*=21) Usual care (booklets for exercise, general advice for nonspecific and persistent low back pain, and acetaminophen) in both groups (n*=11) Wet cupping may have a potential effect on reducing pain associated with nonspecific and persistent low back pain.
Lauche R et al.
(2011) (27) To determine whether a number of cupping treatments effectively relieves chronic nonspecific cervical pain. In addition, the subjects' mechanical thresholds were measured to determine whether cupping therapy has an effect on mechanical hyperalgesia in patients with chronic neck pain.
Cupping therapy and non-steroid medication for pain and physical therapy (n*=22) Non-steroid medication for pain and physical therapy (n*=24) Five dry cupping sessions appear to be safe and effective in the treatment of chronic nonspecific cervical pain.
Farhadi K et al. (33) To determine the effectiveness of Wet Cupping for the treatment of persistent and nonspecific low back pain.
The characterization of the studies regarding the objective, the interventions applied in the experimental and control groups, and the main findings are presented in Figure 2.
Regarding the methodological quality of the RCTs, all reported the random sequence generation method and in only one study (9) this process was not appropriate.
In another study (30) there is not enough information to infer this information. Only in four RCTs (22,24,(28)(29) there was a description of masking and in only two (22,28) this was considered appropriate. Loss of follow-up was not described in only one RCT (29) .
The studied outcomes, the measurement tools, the number of evaluations and the interval between them are described in Figure 3.
The characteristics of the intervention protocol were based on the recommendations of the Revised
Only 18,75% of the studies (n = 3) presented the time of experience of the professional who performed the intervention, from three (35)(36) to four years (34) ; 37.5% of the studies (n=6) (9,(22)(23)(24)(25)27) informed only that the intervention had been performed by experienced or trained professionals, but did not mention the time of training.
Of the 16 articles selected for the systematic review, 10 entered for meta-analysis that investigated the effectiveness of cupping therapy on pain intensity.
All of them approached the outcome in two comparison groups (experimental and control), in evaluations performed before and immediately after the treatment.
Five studies (9,22,29,(35)(36) did not enter because they did not have enough data for this analysis and one study (33) performed the evaluation only three months after the end of treatment.
The results of the meta-analysis showed that cupping therapy was more effective in reducing pain according to the Jadad scale (19) . This score can be justified by the lack of masking of RCTs.
It is not feasible to conceal evaluation and intervention methods in cupping therapy (22) , since the marks left by the suction cups are often visible and may persist for several days, making it difficult to perform a masking process (27) . Only one study (28) achieved masking properly; however, it was true only for volunteers who received laser therapy, an intervention used concomitantly with cupping therapy, where sham laser acupuncture was performed by applying the same procedure in one of the groups, but without energy. In a second study (24) , there is a description that the masking was applied to the evaluator of the results; however, the application of suction cups causes marks (ecchymoses, petechiae) and one of the evaluated outcomes was the pain threshold, using the algometer; for this evaluation, as the area must be naked, the marks on the skin make this kind of masking impossible. Finally, Rev. Latino-Am. Enfermagem 2018;26:e3094.
in another study (22) , the majority of participants in the minimal cupping group (84%) was able to identify the allocation after four weeks, whereas in the cupping group 55% identified the allocation.
Although and severe (7-10), and are frequently used in patients with chronic musculoskeletal pain (37) . In addition, some researchers (38)(39)(40) have pointed to these two scales as the gold standard for assessing pain intensity, these being the instruments most used when evaluating adults, both in clinics and research.
In fact, the severity and chronicity of back pain are associated with severe functional limitations (37) that imply limitations in activities of daily living (41) .
Finally, the physiological parameter most evaluated in the studies was the nociceptive threshold before the mechanical stimulus, by means of a pressure algometer (9,(23)(24)(25)(26)(27) . It is known that individuals who have pain in the spine have higher nociceptive sensitivity compared to healthy people (43) . However, this is still considered a subjective variable, since it is the patient who determines his/her pain threshold. In fact, when the evaluation process is more related to the symptoms, such as subjective phenomena, especially pain, than to physical or laboratory results, self-assessment is considered the most reliable indicator of the existence of pain (44) . Thus, the necessary information to carry out its evaluation has its origin in the individual's report (45) , who is the primary source of the assessment.
The systematized analysis of cupping therapy application methods showed that there is no standardization in the treatment protocol for chronic back pain. However, recent efforts have been made to standardize the cupping therapy procedure in general (46) and specifically for chronic back pain, since the most appropriate type of technique, duration of treatment, number of sessions, devices, time of application, method and suction strength and application points have not been determined.
This modality allows the stimulation of the acupoints in the same way as the acupuncture needles (47) .
Researchers (18) suggest that laceration of the skin and capillaries, promoted by wet cupping, may act as another nociceptive stimulus that activates the descending inhibitory pathways of pain control (18) , thus helping to treat chronic musculoskeletal conditions (35) .

However, risk for infection, vasovagal attacks and scars
are the disadvantages of this method (18) . Still, compared to cupping massage, authors (47) emphasize that dry cupping has a greater analgesic effect, since the use of lubricants can reduce the friction between the edge of the cup and the skin, a fact corroborated by some authors (24) who used arnica oil for the realization of cupping massage.
Despite the variability in the application of the intervention, it was possible to identify that, on average, the cupping therapy was applied in 5 sessions, with permanence of the cups in the skin for around 8 minutes, and interval of three to four days between the applications. According to some researchers (27) , at least five sessions are required for any significant effects of cupping treatment to appear, in addition to ensuring the feasibility of the RCT. Moreover, authors (47) recommend that the cups should be left on the skin for 5 to 10 minutes or more, which culminates in the appearance of residual marks after treatment as a result of the rupture of small blood vessels that are painless and disappear between 1 and 10 days (12) . Therefore, an interval between sessions is necessary in order to allow the reestablishment of the cutaneous and subcutaneous tissues.
Regarding the application cups, the disposable ones are preferable a high-level sterilization or disinfection process is required prior to reuse, since the pressure exerted may cause extravasation of blood and fluids from the skin (46) . Nowadays, cupping therapy has increasingly been performed with plastic cups (47) . The size of the cups varies according to the place of application, but it is often applied in places with abundant muscles, such as the back (48) .
followed by manual pumping (23,(34)(35)(36) and automatic pumping (22,26,33) . Suction with fire is the traditional method used in China, however, there is a risk of burns (18) . Manual vacuum is created when using a suction pump. This method allows microcirculation to increase more effectively if compared to fire (18) . Finally, automatic pumping is created using an electric suction pump, which allows to adjust and measure the negative pressure inside the cup, being the most suitable method for scientific research (18) .
Only three studies (22,26,28) reported the suction strength used, which should be standardized in the application protocols. The suction can be light (100 and 300 millibar/one or two manual pumpings), medium (300 and 500 milibar/three or four manual pumpings), strong (above 500 milibar/five or more manual pumpings) or pulsatile (pressure inside the cups is variable, between 100 and 200 milibar every 2 seconds) (47,49) . The medium suction is often indicated for painful conditions of the musculoskeletal system (18) .
There was also no standardization in relation to the application points of cupping therapy. Despite this, the application in specific acupoints in the cervical region, mainly on the bladder, gallbladder and small intestine meridians, prevailed (29,34) , and in the lumbar region on the bladder meridian (30)(31)(32)(35)(36) , followed by sensitive points (9,(25)(26)(27)30) named Ashi by TCM or trigger points by Western medicine.
Meridians are passages for the flow of "qi" (vital energy) and "xue" (blood), the two basic body fluids of TCM, which spread throughout the body surface, uniting the interior with the exterior of the body and connecting the internal organs, the joints and the extremities, transforming the whole body into a single organ (50) . Part of the meridians of the bladder, small intestine and gallbladder pass through the dorsal region.
The acupuncture points are located in the meridians; besides local action, they also play a systemic action and reestablish the energy balance of the body by adjusting the function of the organs, maintaining homeostasis and treating the disease (51) , so the advantage in using them.
The trigger points or Ashi are specific points of high irritability; they are sensitive to digital pressure and can trigger local and referred pain (52) . They may be deriving from dynamic overload, such as trauma or overuse, or static overload, such as postural overloads occurring during daily activities and occupational activities (53) , besides emotional tension. Addressing these points can also be a way to relieve local pain (54) .
After the application of cupping therapy, both the acupoints of the meridians of the affected regions and the trigger points or Ashi may present bruising, erythema and/or ecchymoses. According to TCM, these signs represent stagnation of "qi" and/or "xue" and may help the therapist in identifying body disorders.
Finally, the meta-analysis revealed a significant reduction of the pain intensity score in adults with chronic back pain by using cupping therapy (p = 0.001).
Compared with a control group (usual care/other intervention/waiting list), this modality has advantages in relieving pain, as can be seen in Figure 5.
Only two studies (24,30) did not present a statistically significant difference between the groups on the benefit or harm of this intervention ( Figure 5). In fact, the first study (24) pointed out that cupping therapy has the same effect as other intervention (progressive muscle relaxation) in reducing chronic nonspecific neck pain; despite this, cupping therapy was better than relaxation in improving well-being and decreasing sensitivity to pressure pain. The authors (24) justify this result, among other limitations, due to the fact that cupping therapy was performed by patients' relatives or friends at home.
The second study (30) , despite having found a positive result on the intensity of pain, did not obtain a result in the meta-analysis. It is believed that this may have been due to the fact that both groups received the intervention of soft cupping and both obtained positive results.
In fact, all these studies reported promising results of intervention on pain intensity.
However, the results of the effectiveness of cupping therapy still need to be confirmed by subgroup analyzes, based on different types of application techniques and control groups. In addition, it is important to perform meta-regression to find the source of heterogeneity of RCTs.
In a general way, the results showed a substantial variation in the application of cupping therapy, especially in relation to the type of technique, as well as differences in the control group, which made subgroup or metaregression unfeasible, respectively, due to the small number of studies with each of these specifications.

Conclusion
Cupping therapy is a promising method for the treatment and control of chronic back pain in adults, since it significantly decreases pain intensity scores when compared to control groups. However, the high heterogeneity and the median methodological quality of RCTs has limited the findings.
Despite this, a protocol can be established for this clinical condition: application of dry cupping technique Rev. Latino-Am. Enfermagem 2018;26:e3094.
in 5 sessions, with permanence of the disposable or plastic cups on the skin for about 8 minutes, preferably automatic or manual pumping, with medium suction strength, and three to seven days interval between applications. It is better to opt for acupoints of the dorsal region, especially those from the bladder meridian in the lumbar region, and for the meridians of the bladder, gallbladder and small intestine in the cervical and thoracic regions, as well as Ashi or trigger points.
This protocol needs to be validated in future studies.
And the main outcomes evaluated for this clinical condition were pain intensity, physical disability, quality of life and nociceptive threshold before the mechanical stimulus (pressure).