Abstract

Objective. This article is aimed at critically evaluating the evidence from systematic reviews (SRs) of spinal manipulation in patients with pain.

Design. The study was designed as a SR of SRs.

Methods. Four electronic databases were searched to identify all relevant articles of the effectiveness of spinal manipulation for pain. SRs were defined as articles employing a repeatable methods section.

Results. Twenty-two SRs relating to the following pain conditions: low back pain (N = 6), headache (N = 5), neck pain (N = 4), any medical problem (N = 1), carpal tunnel syndrome (N = 1), dysmenorrhea (N = 1), fibromyalgia (N = 1), lateral epicondylitis (N = 1), musculoskeletal conditions (N = 1) and nonspinal pain (N = 1), were included. Positive or, for multiple SR, unanimously positive conclusions were drawn for none of the conditions mentioned earlier.

Limitation. Publication bias as a well-known phenomenon may have been inherited in this article.

Conclusion. Collectively, these data fail to demonstrate that spinal manipulation is an effective intervention for pain management.

Introduction

Pain is prevalent and often difficult to treat. It is associated with a high burden of suffering and considerable socio-economic costs. Among the many treatments that are being suggested is spinal manipulation (SM). SM is a technique commonly used by chiropractors, osteopaths, physiotherapists, physicians, bone setters or other manual therapists. SM can be defined as “the application of high-velocity, low-amplitude manual thrusts to the spinal joints slightly beyond the passive range of joint motion”[1]. This technique aims to correct misalignments or so called subluxations of the joints (both spinal and peripheral) [2]. However, it has been suggested that subluxations lack biological plausibility [3,4]. Safety and cost-effectiveness of SM have also been questioned [5–8]. Despite unproven safety, debatable effectiveness and cost-effectiveness, SM is still widely used for a wide range of pain related conditions (among others).

Hundreds of randomized clinical trials (RCTs) of SM have been published in the literature; however, their data are less than uniform. To date, systematic reviews (SRs) are considered to be at the top of evidence-base hierarchy and may therefore provide the most conclusive answer regarding the effectiveness of SM for pain management. Unfortunately, the evaluations of the effectiveness of SM often arrive at contradictory conclusions. In order to make progress in this area, we need rigorous SRs, which include the totality of the available evidence on a clearly defined population, precise therapeutic interventions and types of pain included. Until such SRs are available, it is highly problematic to draw firm conclusions regarding the therapeutic value of SM for pain.

The aim of this article was to critically evaluate the data from SRs of SM as a pain management option.

Methods

The author conducted literature searches to identify all SRs of SM for any pain-related condition. Searches were conducted in the following electronic databases (from their inception to March 2011): Medline, Embase, AMED, and Cochrane Database. The following search terms were used: [Chiropract* OR spinal manipul* OR manual therap* OR osteopath*] AND [systematic ADJ review]. No language barriers were imposed.

After initial screening of abstracts, those meeting the inclusion criteria were retrieved for further evaluation by the author. SRs were defined as articles that included an explicit and repeatable methods section. To be included, SRs had to pertain to the effectiveness of SM for any type of pain or pain-related condition and to include evidence from at least one controlled clinical trial. Only SRs that included evidence from RCTs were included because this reduces the risk of bias according to the Cochrane Collaboration. SRs of SM as a part of complex therapeutic interventions were excluded. Update reviews were also excluded.

One author extracted the data from the identified articles according to predefined criteria (Table 1), and evaluated the methodological quality of each SR according to Oxman and Guyatt [9] (Table 2). The Oxman criteria for SRs evaluate the comprehensiveness and thoroughness of search strategy, eligibility criteria, validity assessment, and quantitative analysis (a total of nine items is evaluated). Each question is scored as 1 (fulfilled), 0 (partially fulfilled), or −1 (not fulfilled). A score of 5 or less means the review has extensive or major flaws, and a score of 6–9 means that the review has minimal or no flaws.

Table 1

Systematic reviews of spinal manipulations for pain

First author (year) (ref) Interventions Condition Treated N (RCTs) Meta-analysis Overall Result (quote) Direction of Conclusion Comment 
Assendelft et al. (2004) [10] Any type of SM Low back pain 39 Yes No evidence that SM is superior to other standard treatments for acute or chronic low back pain (−) RCTs of mobilization were also included 
Bronfort et al. (2004) [11] SM and mobilization Low back pain and neck pain 69 No . . . recommendations can be made with some confidence regarding the use of SM and/or mobilization as a viable option for treatment of both low back pain and neck pain (+) Conclusions based on 43 RCTs meeting admissibility criteria for evidence 
Dagenais et al. (2010) [12] SM Acute low back pain 14 No Several RCTs have been conducted to assess the efficacy of SMT for acute LBP using various methods (+)  
Ernst and Canter (2003) [13] Chiropractic SM Low back pain 12 No Effectiveness . . . not supported by compelling evidence from the majority of RCTs (−) Focus exclusively on SM as performed by chiropractors 
Ferreira et al. (2002) [14] SM Chronic low back 12 Yes (SM) . . . is not substantially more effective than sham treatment in reducing pain, nor is it more effective than NSAIDs in improving disability in chronic low back pain patients. It is not clear whether. . . . (SM) . . . is more effective than NSAIDs in reducing pain in chronic low back pain patients (−) Mostly moderate quality data was included 
Licciardone et al. (2005) [15] Osteopathic manipulative therapy Low back pain  6 Yes Osteopathic manipulative therapy significantly reduces low back pain. The level of pain reduction is greater than expected from placebo effects alone and persists for at least three months. (+) Significant heterogeneity of meta-analyzed data 
Astin and Ernst (2002) [16] Any type of SM Headache disorders  8 No The data available to date do not support . . . that SM is an effective treatment for headache (−) Rigorous systematic review 
Bronfort et al. (2001) [1] SM Chronic headache  9 No SM appears to have a better effect than massage for cervicogenic headache . . . an effect comparable to commonly used first line prophylactic prescription medications for tension-type headache and migraine headache. This conclusion rests upon a few trials of adequate methodological quality. Before any firm conclusions can be drawn, further testing should be done. (+) Only nine primary studies included 
Fernández de las Peńas et al. (2006) [17] Any type of manual therapy including SM Tension type headache  6 No The author found no rigorous evidence that manual therapies have a positive effect in the evolution of TTH. The most urgent need for further research is to establish the efficacy beyond placebo of the different manual therapies currently applied in patients with TTH. (−) Different manual therapy modalities were included 
Fernández de las Peńas et al. (2005) [18] SM Cervicogenic headache  2 No Spinal manipulative therapy might be effective in reducing headache intensity, headache duration, medication intake (level 1), and headache frequency (level 3) in patients with CeH. (+) Low quantity of the data 
Lenssinck et al. (2004) [19] Physiotherapy and/or spinal manipulation Tension type headache  8 No There is insufficient evidence to either support or refute the effectiveness of physiotherapy and (SM) compared with other treatments. (−) Included five RCTs of SM including two high-quality RCTs of chiropractic with contradictory results 
Ernst (2003) [20] Chiropractic SM Neck pain  4 No The notion that chiropractic SM is more effective than conventional exercise . . . was not supported by rigorous trial data (−) Focus exclusively on SM as performed by chiropractors 
Gross et al. (2004) [21] Any type of SM and mobilization Neck problems 33 Yes The evidence did not favor manipulation and/or mobilization done alone or in combination with various other physical medicine agents; when compared with one another, neither was superior. There was insufficient evidence available to draw conclusions for neck disorder with radicular findings. (−) 42% of the included data was of high quality 
Gross et al. (2010) [22] SM or mobilization Neck pain, headache, whiplash injuries 27 Yes Cervical manipulation and mobilization produced similar changes. Either may provide immediate- or short-term change; no long-term data are available. Thoracic manipulation may improve pain and function. Optimal techniques and dose are unresolved. Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. (+/−) Low to moderate quality evidence was included 
Vernon et al. (2005) [23] SM, manual therapy and TENS Acute neck pain not due to whiplash  4 No There is limited evidence of the benefit of spinal manipulation . . . in the treatment of acute neck pain not due to whiplash injury. (−) Combination of modalities included 
Posadzki (2010) [24] Osteopathic manipulation Musculoskeletal pain 16 No The notion that osteopathic manipulative therapy alleviates musculoskeletal pain is currently not based on the evidence from independently replicated high quality clinical trials. (−) Various quality RCTs were considered 
Ernst (2003) [25] Chiropractic SM Non-spinal pain syndromes  8 No The claim that SM is effective for such conditions is not based on data from rigorous clinical studies (−) Conditions included fibromyalgia, carpal tunnel syndrome, infantile colic, otitis media, dysmenorrhea and chronic pelvic pain 
Ernst [2009][26] Chiropractic SM Fibromyalgia  3 No There is no evidence to suggest that chiropractic care is effective for fibromyalgia (−) Poor quality and low quantity of the primary data 
Herd (2008) [27] SM or mobilization Lateral epicondylitis 13 No Currently, limited evidence exists to support a synthesis of any particular technique whether directed at the elbow or cervical spine. (−) The presence of consistent methodological flaws was reported 
Hunt et al. (2009) [28] Chiropractic SM Carpal tunnel syndrome  1 No There is insufficient evidence to suggest that chiropractic is effective for the treatment of CTS. Therapy should continue to focus on the use of NSAIDs, corticosteroid injection, splinting and surgical release of the median nerve. Further research into the utility of chiropractic for CTS is required. (−)  
Proctor et al. (2001) [29] Any type of SM Primary and secondary dysmenorrhea  5 No There is no evidence that SM is effective (−) Four of the five RCTs were of high velocity, low amplitude thrusts 
First author (year) (ref) Interventions Condition Treated N (RCTs) Meta-analysis Overall Result (quote) Direction of Conclusion Comment 
Assendelft et al. (2004) [10] Any type of SM Low back pain 39 Yes No evidence that SM is superior to other standard treatments for acute or chronic low back pain (−) RCTs of mobilization were also included 
Bronfort et al. (2004) [11] SM and mobilization Low back pain and neck pain 69 No . . . recommendations can be made with some confidence regarding the use of SM and/or mobilization as a viable option for treatment of both low back pain and neck pain (+) Conclusions based on 43 RCTs meeting admissibility criteria for evidence 
Dagenais et al. (2010) [12] SM Acute low back pain 14 No Several RCTs have been conducted to assess the efficacy of SMT for acute LBP using various methods (+)  
Ernst and Canter (2003) [13] Chiropractic SM Low back pain 12 No Effectiveness . . . not supported by compelling evidence from the majority of RCTs (−) Focus exclusively on SM as performed by chiropractors 
Ferreira et al. (2002) [14] SM Chronic low back 12 Yes (SM) . . . is not substantially more effective than sham treatment in reducing pain, nor is it more effective than NSAIDs in improving disability in chronic low back pain patients. It is not clear whether. . . . (SM) . . . is more effective than NSAIDs in reducing pain in chronic low back pain patients (−) Mostly moderate quality data was included 
Licciardone et al. (2005) [15] Osteopathic manipulative therapy Low back pain  6 Yes Osteopathic manipulative therapy significantly reduces low back pain. The level of pain reduction is greater than expected from placebo effects alone and persists for at least three months. (+) Significant heterogeneity of meta-analyzed data 
Astin and Ernst (2002) [16] Any type of SM Headache disorders  8 No The data available to date do not support . . . that SM is an effective treatment for headache (−) Rigorous systematic review 
Bronfort et al. (2001) [1] SM Chronic headache  9 No SM appears to have a better effect than massage for cervicogenic headache . . . an effect comparable to commonly used first line prophylactic prescription medications for tension-type headache and migraine headache. This conclusion rests upon a few trials of adequate methodological quality. Before any firm conclusions can be drawn, further testing should be done. (+) Only nine primary studies included 
Fernández de las Peńas et al. (2006) [17] Any type of manual therapy including SM Tension type headache  6 No The author found no rigorous evidence that manual therapies have a positive effect in the evolution of TTH. The most urgent need for further research is to establish the efficacy beyond placebo of the different manual therapies currently applied in patients with TTH. (−) Different manual therapy modalities were included 
Fernández de las Peńas et al. (2005) [18] SM Cervicogenic headache  2 No Spinal manipulative therapy might be effective in reducing headache intensity, headache duration, medication intake (level 1), and headache frequency (level 3) in patients with CeH. (+) Low quantity of the data 
Lenssinck et al. (2004) [19] Physiotherapy and/or spinal manipulation Tension type headache  8 No There is insufficient evidence to either support or refute the effectiveness of physiotherapy and (SM) compared with other treatments. (−) Included five RCTs of SM including two high-quality RCTs of chiropractic with contradictory results 
Ernst (2003) [20] Chiropractic SM Neck pain  4 No The notion that chiropractic SM is more effective than conventional exercise . . . was not supported by rigorous trial data (−) Focus exclusively on SM as performed by chiropractors 
Gross et al. (2004) [21] Any type of SM and mobilization Neck problems 33 Yes The evidence did not favor manipulation and/or mobilization done alone or in combination with various other physical medicine agents; when compared with one another, neither was superior. There was insufficient evidence available to draw conclusions for neck disorder with radicular findings. (−) 42% of the included data was of high quality 
Gross et al. (2010) [22] SM or mobilization Neck pain, headache, whiplash injuries 27 Yes Cervical manipulation and mobilization produced similar changes. Either may provide immediate- or short-term change; no long-term data are available. Thoracic manipulation may improve pain and function. Optimal techniques and dose are unresolved. Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. (+/−) Low to moderate quality evidence was included 
Vernon et al. (2005) [23] SM, manual therapy and TENS Acute neck pain not due to whiplash  4 No There is limited evidence of the benefit of spinal manipulation . . . in the treatment of acute neck pain not due to whiplash injury. (−) Combination of modalities included 
Posadzki (2010) [24] Osteopathic manipulation Musculoskeletal pain 16 No The notion that osteopathic manipulative therapy alleviates musculoskeletal pain is currently not based on the evidence from independently replicated high quality clinical trials. (−) Various quality RCTs were considered 
Ernst (2003) [25] Chiropractic SM Non-spinal pain syndromes  8 No The claim that SM is effective for such conditions is not based on data from rigorous clinical studies (−) Conditions included fibromyalgia, carpal tunnel syndrome, infantile colic, otitis media, dysmenorrhea and chronic pelvic pain 
Ernst [2009][26] Chiropractic SM Fibromyalgia  3 No There is no evidence to suggest that chiropractic care is effective for fibromyalgia (−) Poor quality and low quantity of the primary data 
Herd (2008) [27] SM or mobilization Lateral epicondylitis 13 No Currently, limited evidence exists to support a synthesis of any particular technique whether directed at the elbow or cervical spine. (−) The presence of consistent methodological flaws was reported 
Hunt et al. (2009) [28] Chiropractic SM Carpal tunnel syndrome  1 No There is insufficient evidence to suggest that chiropractic is effective for the treatment of CTS. Therapy should continue to focus on the use of NSAIDs, corticosteroid injection, splinting and surgical release of the median nerve. Further research into the utility of chiropractic for CTS is required. (−)  
Proctor et al. (2001) [29] Any type of SM Primary and secondary dysmenorrhea  5 No There is no evidence that SM is effective (−) Four of the five RCTs were of high velocity, low amplitude thrusts 

CTS = carpal tunnel syndrome; LBP = low back pain; NSAIDs = nonsteroid anti-inflammatory drugs; SM = spinal manipulation; SMT = spinal manipulative therapy; RCT = randomized clinical trial; TENS = transcutaneous electrical nerve stimulation; TTH = tension type headache.

Table 2

Quality ratings for included systematic reviews of spinal manipulations for pain

Study, year (ref) Search Methods? (a) Search Comprehensive? (b) Inclusion Criteria? (c) Bias Avoided? (d) Validity Criteria? (e) Validity Assessed? (f) Methods for Combining Studies? (g) Appropriately Combined? (h) Conclusions Supported? (i) Sum 
Assendelft et al.(2004) [10]  1  1  1  1  1  1  1  1  9 
Astin and Ernst (2002) [16]  1  1  1  1  1  1  1  1  9 
Bronfort et al. (2001) [1]  1  1  1  1  0  1  0  1  7 
Bronfort et al. (2004) [11]  1  1  0  1  1  1  0  0  6 
Dagenais et al. (2010) [12] −1  0  1  1  1 −1 −1  0  1 
Ernst and Harkness (2001) [30]  1  1  1  1  1  1 −1  1  8 
Ernst and Canter (2003) [13]  1  1  1  1  1  1 −1  1  8 
Ernst (2003) [20]  1  1  1  1  1  1 −1  1  8 
Ernst (2003) [25]  1  1  1  1  1  1 −1  1  8 
Ernst (2009) [26]  1  1  1  1  1 −1 −1  1  7 
Fernández de las Peńas et al. (2006) [17]  1  0  0  1  0  1  1  1  6 
Fernández de las Peńas et al. (2005) [18]  0 −1 −1  1  0 −1 −1 −1 −3 
Ferreira (2002) [14]  1  1  1  1  1  1  1  1  9 
Gross et al. (2004) [21]  1  1  0  1  1  1  1  1  8 
Gross et al. (2010) [22]  0  1  0  1  1  1  1  1  7 
Herd (2008) [27]  1  1  1  0  0  0  0  0  4 
Hunt et al. (2009) [28]  1  1  1  1  1  1  1  1  9 
Lenssinck et al. (2004) [19]  1  1  1  1  1  1  0  1  8 
Licciardone et al. (2005) [15]  1  1  0 −1 −1  1  1 −1  2 
Posadzki (2010) [24]  1  1  1  1  1  1  0  1  8 
Proctor et al. (2001) [29]  1  1  1  1  1  1  0  1  8 
Vernon et al. (2005) [23]  1  0 −1  0  0  0  0  0  1 
Study, year (ref) Search Methods? (a) Search Comprehensive? (b) Inclusion Criteria? (c) Bias Avoided? (d) Validity Criteria? (e) Validity Assessed? (f) Methods for Combining Studies? (g) Appropriately Combined? (h) Conclusions Supported? (i) Sum 
Assendelft et al.(2004) [10]  1  1  1  1  1  1  1  1  9 
Astin and Ernst (2002) [16]  1  1  1  1  1  1  1  1  9 
Bronfort et al. (2001) [1]  1  1  1  1  0  1  0  1  7 
Bronfort et al. (2004) [11]  1  1  0  1  1  1  0  0  6 
Dagenais et al. (2010) [12] −1  0  1  1  1 −1 −1  0  1 
Ernst and Harkness (2001) [30]  1  1  1  1  1  1 −1  1  8 
Ernst and Canter (2003) [13]  1  1  1  1  1  1 −1  1  8 
Ernst (2003) [20]  1  1  1  1  1  1 −1  1  8 
Ernst (2003) [25]  1  1  1  1  1  1 −1  1  8 
Ernst (2009) [26]  1  1  1  1  1 −1 −1  1  7 
Fernández de las Peńas et al. (2006) [17]  1  0  0  1  0  1  1  1  6 
Fernández de las Peńas et al. (2005) [18]  0 −1 −1  1  0 −1 −1 −1 −3 
Ferreira (2002) [14]  1  1  1  1  1  1  1  1  9 
Gross et al. (2004) [21]  1  1  0  1  1  1  1  1  8 
Gross et al. (2010) [22]  0  1  0  1  1  1  1  1  7 
Herd (2008) [27]  1  1  1  0  0  0  0  0  4 
Hunt et al. (2009) [28]  1  1  1  1  1  1  1  1  9 
Lenssinck et al. (2004) [19]  1  1  1  1  1  1  0  1  8 
Licciardone et al. (2005) [15]  1  1  0 −1 −1  1  1 −1  2 
Posadzki (2010) [24]  1  1  1  1  1  1  0  1  8 
Proctor et al. (2001) [29]  1  1  1  1  1  1  0  1  8 
Vernon et al. (2005) [23]  1  0 −1  0  0  0  0  0  1 

Scoring: Each Question is Scored as 1, 0, or −1.

1 = (a) the review states the databases used, date of most recent searches, and some mention of search terms; (b) the review searches at least two databases and looks at other sources; (c) the review states the criteria used for deciding which studies to include in the overview; (d) the review reports how many studies were identified by searches, numbers excluded, and appropriate reasons for excluding them; (e) the review states the criteria used for assessing the validity of the included studies; (f) the review reports validity assessment and did some type of analysis with it; (g) the report mentions that quantitative analysis was not possible and reasons that it could not be done; (h) the review performs a test for heterogeneity before pooling or does appropriate subgroup testing, appropriate sensitivity analysis, or other such analysis; (i) the conclusions made by the author(s) are supported by the data and/or analysis reported in the review; 0 = the above mentioned criteria were partially fulfilled; −1 = none of the above criteria were fulfilled.

A score of 1 or less means the review has extensive flaws, 2–5 major flaws, and 6–9 minimal or no flaws.

Operationalization of the Oxman criteria [9], adapted from Chou and Huffman [37].

Data were analyzed using Predictive Analytics Software Statistics 18.0.1.

Results

After removal of duplicates, the searches generated 62 articles. Forty articles were excluded (Figure 1). The reasons for exclusion were: not SRs (N = 14), not pain-related condition (N = 13) based on previous SR (N = 7), and SRs that did not include RCTs only (N = 6). Twenty-two SRs met the inclusion criteria mentioned earlier [1,10–30]. Key data of these reviews are summarized in Table 1. These SRs related to the following conditions: low back pain (LBP) (N = 6), headache (N = 5), neck pain (N = 4), any medical problem (N = 1), carpal tunnel syndrome (N = 1), dysmenorrhea (N = 1), fibromyalgia (N = 1), lateral epicondylitis (N = 1), musculoskeletal conditions (N = 1), and nonspinal pain (N = 1). There was some overlap between these categories (Table 3).

Figure 1

Flowchart of eligibility assessment and inclusion. RCT = randomized control trials; SR = systematic review.

Figure 1

Flowchart of eligibility assessment and inclusion. RCT = randomized control trials; SR = systematic review.

Table 3

Conditions with multiple systematic reviews

 Conclusion
 
Condition Positive Negative Neutral or unclear 
Headache 
Low back pain 
Neck pain 
 Conclusion
 
Condition Positive Negative Neutral or unclear 
Headache 
Low back pain 
Neck pain 

The SRs included chiropractic or osteopathic manipulations as well as manual therapy or any type of SM. Nine SRs included more than 10 primary studies [10–14,21,22,24,27]; and five included a meta-analytic approach [10,14,15,21,22]. The conclusions drawn from most SRs were frequently cautious or negative (Table 1).

For instance, for LBP three SRs arrived at positive conclusions [11,12,15], and three arrived at negative conclusions [10,13,14]. For headaches, two reached positive conclusions [1,18] whereas three reached negative conclusions [16,17,19]. For neck pain, three arrived at negative conclusions [20,21,23] and one arrived at equivocal conclusions [22]. Thus, there was an undeniable degree of contradiction between these SRs.

The methodological quality of SRs was predominantly high—17 SRs were of high quality and five were of poor quality (Mean = 6.23, standard deviation = 3.23). However, the quality of SRs published by independent authors was significantly higher than those published by chiropractors/osteopaths. There was a statistically significant difference between groups as determined by one-way analysis of variance (F[1,3] = 82.371, P = 0.003).

Discussion

In the recent years, dozens of SRs investigating the therapeutic value of SM in a wide variety of pain-related conditions have been published. The present article was aimed at critically evaluating the data for or against the notion that SM is effective in treating pain in human subjects.

Twenty-two SRs met the eligibility criteria [1,10–30]. Five of those 22 SRs suggested that SM is effective [1,11,12,15,18], and 17 failed to do so [10,13,14,16,17,19–30]. Therefore, most of these SRs (77%) failed to produce convincing evidence to suggest that SM is of effective therapeutic value for pain.

It is suggested that the conclusions of SRs of SM for back pain appear to be influenced by authorship. Osteopaths or chiropractors seem to publish low methodological-quality SRs associated with positive conclusions (Table 4). Four (80%) of the five SRs published either by chiropractors or osteopaths arrived at overtly positive conclusions [1,11,12,15] and only one arrived at negative conclusions [23]. Sixteen (94%) of the 17 SRs by independent research groups reached negative or equivocal conclusions [10,13,14,16,17,19–30]. Only one (6%) arrived at positive conclusions [18]. Therefore, this review shows that SM is of debatable clinical usefulness in pain management.

Table 4

Summary of findings

Study (year) (ref) Quality of systematic review (Oxman criteria) Chiropractors or osteopaths as first authors Conclusions 
Assendelft et al. [2004][10]  9 No (−) 
Astin and Ernst (2002) [16]  9 No (−) 
Bronfort et al. (2001) [1]  7 Yes (+) 
Bronfort et al. (2004) [11]  6 Yes (+) 
Dagenais et al. (2010) [12]  1 Yes (+) 
Ernst and Harkness (2001) [30]  8 No (−) 
Ernst and Canter (2003) [13]  8 No (−) 
Ernst (2003) [20]  8 No (−) 
Ernst (2003) [25]  8 No (−) 
Ernst (2009) [26]  7 No (−) 
Fernández de las Peńas et al. (2006) [17]  6 No (−) 
Fernández de las Peńas et al. (2005) [18] −3 No (+) 
Ferreira (2002) [14]  9 No (−) 
Gross et al. (2004) [21]  8 No (−) 
Gross et al. (2010) [22]  7 No (+/−) 
Herd (2008) [27]  4 No (−) 
Hunt et al. (2009) [28]  9 No (−) 
Lenssinck et al. (2004) [19]  8 No (−) 
Licciardone et al. (2005) [15]  2 Yes (+) 
Posadzki (2010) [24]  8 No (−) 
Proctor et al. (2001) [29]  8 No (−) 
Vernon et al. (2005) [23]  1 Yes (−) 
Study (year) (ref) Quality of systematic review (Oxman criteria) Chiropractors or osteopaths as first authors Conclusions 
Assendelft et al. [2004][10]  9 No (−) 
Astin and Ernst (2002) [16]  9 No (−) 
Bronfort et al. (2001) [1]  7 Yes (+) 
Bronfort et al. (2004) [11]  6 Yes (+) 
Dagenais et al. (2010) [12]  1 Yes (+) 
Ernst and Harkness (2001) [30]  8 No (−) 
Ernst and Canter (2003) [13]  8 No (−) 
Ernst (2003) [20]  8 No (−) 
Ernst (2003) [25]  8 No (−) 
Ernst (2009) [26]  7 No (−) 
Fernández de las Peńas et al. (2006) [17]  6 No (−) 
Fernández de las Peńas et al. (2005) [18] −3 No (+) 
Ferreira (2002) [14]  9 No (−) 
Gross et al. (2004) [21]  8 No (−) 
Gross et al. (2010) [22]  7 No (+/−) 
Herd (2008) [27]  4 No (−) 
Hunt et al. (2009) [28]  9 No (−) 
Lenssinck et al. (2004) [19]  8 No (−) 
Licciardone et al. (2005) [15]  2 Yes (+) 
Posadzki (2010) [24]  8 No (−) 
Proctor et al. (2001) [29]  8 No (−) 
Vernon et al. (2005) [23]  1 Yes (−) 

Score 6–9 indicates high quality; score 5 or less indicates low quality.

(−) negative; (+) positive; (+/−) equivocal.

The highest degree of ambiguity in the included SRs has been noticed for LBP. There was a 3/3 ratio of positive vs negative SRs, meaning that more research need to be done in order to determine the effectiveness of SM for that condition. A less favorable ratio has been noticed for headaches (2/3), meaning that for some types of headaches and in certain groups of patients, SM is ineffective. The worst ratio has been noticed for neck pain. There was one equivocal SR vs three negative ones, meaning that SM should not be the recommended treatment option for patients with neck pain. For other conditions such as musculoskeletal pain, nonspinal pain syndromes, fibromyalgia, lateral epicondylitis, carpal tunnel syndrome, or primary and secondary dysmenorrhea, the conclusions from SRs were all negative.

Safety of each therapeutic intervention should be of paramount importance. Unfortunately, several hundred severe complications after upper SM have been reported, e.g., [31,32] although the estimates as to the incidence of these complications vary hugely [8]. A particular concern relates to vascular accidents caused by arterial dissection after upper SM [33–36]. Therefore, if the harms outweigh benefits, SM should be discouraged as a treatment option for pain in the cervical area.

However, the present analysis has several limitations. First, although searches were broad, the author cannot be certain that all relevant articles were located. Second, all SRs are prone to a well-known phenomenon—publication bias—which may have been inherited in this study. Also, the fact that only one reviewer extracted the data and performed quality assessment might have caused additional bias.

Future research in this area should control for placebo effects by employing sham SM, using blinded design, and being of adequate sample size based on power calculations. Allocation to groups should be concealed, data analyzed based on intention to treat, and validated outcome measures ought to be used to increase internal validity in future research on SM in pain management.

Conclusion

Clinical decisions always have to be based on weighing the potential benefits of an intervention with its risks when managing pain patients. Until recently, it was relatively unclear whether SM is an effective therapeutic option for pain management. This review demonstrates rather convincingly that SM is an ineffective option in the management of some types of pain such as neck pain; and the risks outweigh the benefits. Further research in other areas such as LBP or headache may seem justified.

Acknowledgments

The author would like to thank Professor Edzard Ernst for his valuable contribution to this manuscript.

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Conflict of interest: None declared.
Source of funding: None.