Benefits and harms of spinal manipulative therapy for the treatment of chronic low back pain: systematic review and meta-analysis of randomised controlled trials
BMJ 2019; 364 doi: https://doi.org/10.1136/bmj.l689 (Published 13 March 2019) Cite this as: BMJ 2019;364:l689
- Sidney M Rubinstein, associate professor1,
- Annemarie de Zoete, doctoral student1,
- Marienke van Middelkoop, associate professor2,
- Willem J J Assendelft, professor3,
- Michiel R de Boer, associate professor1,
- Maurits W van Tulder, professor14
- 1Department of Health Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, Netherlands
- 2Department of General Practice, Erasmus Medical Centre, Rotterdam, Netherlands
- 3Department of Primary and Community Care, Radboud University Medical Centre, Nijmegen, Netherlands
- 4Department of Physiotherapy & Occupational Therapy, Aarhus University Hospital, Aarhus, Denmark
- Correspondence to: S M Rubinstein s.m.rubinstein{at}vu.nl (or @SM_Rubinstein)
- Accepted 7 February 2019
Abstract
Objective To assess the benefits and harms of spinal manipulative therapy (SMT) for the treatment of chronic low back pain.
Design Systematic review and meta-analysis of randomised controlled trials.
Data sources Medline, PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL, Physiotherapy Evidence Database (PEDro), Index to Chiropractic Literature, and trial registries up to 4 May 2018, including reference lists of eligible trials and related reviews.
Eligibility criteria for selecting studies Randomised controlled trials examining the effect of spinal manipulation or mobilisation in adults (≥18 years) with chronic low back pain with or without referred pain. Studies that exclusively examined sciatica were excluded, as was grey literature. No restrictions were applied to language or setting.
Review methods Two reviewers independently selected studies, extracted data, and assessed risk of bias and quality of the evidence. The effect of SMT was compared with recommended therapies, non-recommended therapies, sham (placebo) SMT, and SMT as an adjuvant therapy. Main outcomes were pain and back specific functional status, examined as mean differences and standardised mean differences (SMD), respectively. Outcomes were examined at 1, 6, and 12 months. Quality of evidence was assessed using GRADE. A random effects model was used and statistical heterogeneity explored.
Results 47 randomised controlled trials including a total of 9211 participants were identified, who were on average middle aged (35-60 years). Most trials compared SMT with recommended therapies. Moderate quality evidence suggested that SMT has similar effects to other recommended therapies for short term pain relief (mean difference −3.17, 95% confidence interval −7.85 to 1.51) and a small, clinically better improvement in function (SMD −0.25, 95% confidence interval −0.41 to −0.09). High quality evidence suggested that compared with non-recommended therapies SMT results in small, not clinically better effects for short term pain relief (mean difference −7.48, −11.50 to −3.47) and small to moderate clinically better improvement in function (SMD −0.41, −0.67 to −0.15). In general, these results were similar for the intermediate and long term outcomes as were the effects of SMT as an adjuvant therapy. Evidence for sham SMT was low to very low quality; therefore these effects should be considered uncertain. Statistical heterogeneity could not be explained. About half of the studies examined adverse and serious adverse events, but in most of these it was unclear how and whether these events were registered systematically. Most of the observed adverse events were musculoskeletal related, transient in nature, and of mild to moderate severity. One study with a low risk of selection bias and powered to examine risk (n=183) found no increased risk of an adverse event (relative risk 1.24, 95% confidence interval 0.85 to 1.81) or duration of the event (1.13, 0.59 to 2.18) compared with sham SMT. In one study, the Data Safety Monitoring Board judged one serious adverse event to be possibly related to SMT.
Conclusion SMT produces similar effects to recommended therapies for chronic low back pain, whereas SMT seems to be better than non-recommended interventions for improvement in function in the short term. Clinicians should inform their patients of the potential risks of adverse events associated with SMT.
Introduction
Low back pain is a common and disabling disorder.1 Adequate treatment of low back pain is therefore important for patients, clinicians, and healthcare policy makers. Spinal manipulative therapy (SMT) is widely used to treat low back pain and has been examined in numerous randomised controlled trials of varying methodological quality and size, with varying results. These trials have been summarised in systematic reviews, including an earlier review of ours, and the results form the basis for recommendations in clinical guidelines.2345
The effectiveness of SMT for the treatment of chronic low back pain and therefore recommendations in international guidelines for the use of non-drug interventions in the treatment of non-specific low back pain, are not without dispute.6 In some countries, SMT is considered a first line treatment option,3 whereas in others it is recommended as a component of a broader treatment package including exercise,5 or is not included or mentioned at all.4 The most recent summary of these guidelines suggests that SMT should be considered a second line or adjuvant treatment option, after exercise or cognitive behavioural therapy.7
In this review, we consider SMT to represent any hands-on treatment of the spine, including both mobilisation and manipulation. Mobilisations use low grade velocity, small or large amplitude passive movement techniques within the patient’s range of motion and control, whereas manipulation uses a high velocity impulse or thrust applied to a synovial joint over a short amplitude at or near the end of the passive or physiological range of motion.8 This is often accompanied by an audible crack, resulting from cavitation of the joint.
Many hypotheses about how SMT might work exist.910 The modes of action can be roughly divided into biomechanical and neurophysiological. The mechanistic (biomechanical) approach suggests that SMT acts on a manipulable or functional spinal lesion; the treatment is designed to reduce internal mechanical stresses.1112 The neurophysiological approach suggests that SMT affects the primary afferent neurons from paraspinal tissues, the motor control system, and pain processing.131415161718
To resolve the issue of effectiveness, we conducted a systematic review and meta-analysis. This publication is an update of our earlier Cochrane review, which found high quality evidence suggesting no clinically relevant difference between SMT and effective interventions for reducing pain and improving function in patients with chronic low back pain.19 Data for the other comparisons were of lesser quality.
The primary objective of this current review was to examine the effectiveness of SMT on pain relief and improvement in function at the short, intermediate, and long term follow-up compared with control treatments for adults with chronic low back pain. Secondary objectives included the assessment of adverse events. The effect of SMT for other secondary outcomes, such as recovery, return to work, and health related quality of life are to be fully described elsewhere as an update of this review and published in the Cochrane Library.
Methods
This review follows the guidelines for Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA). Our protocol is registered with the Cochrane Collaboration.20
Criteria for considering studies for this review
We only included published randomised studies. Studies using an inadequate randomisation procedure (eg, alternate allocation, allocation based on birth date) were excluded, as was grey literature.
Studies were considered eligible if they included adults (≥18 years) and if more than 50% of the study population had pain lasting more than three months. Additionally, we included studies if the observed differences were thought to be due to the unique contribution of SMT, which may include studies in which SMT was delivered as part of a package of care—that is, if the effects of SMT could be isolated; for example, studies comparing SMT plus exercise with exercise alone would be included, whereas studies comparing SMT plus exercise with SMT alone would not. We excluded participants with postpartum low back pain or pelvic pain due to pregnancy, pain unrelated to the lower back, postoperative studies, patients with serious pathology, and studies that examined “maintenance care” or prevention; in addition to studies that were designed to test the immediate post-intervention effect of a single treatment only as well as those studies that exclusively examined back related conditions (eg, sciatica). We also excluded studies if SMT was combined with other therapies, making it difficult to distinguish the effect of SMT—for example, a study comparing SMT plus exercise with another type of treatment (eg, general practitioner care).
This review focuses on the effects of both spinal manipulation (high velocity, low amplitude (HVLA) techniques) as well as mobilisation (low velocity, low amplitude (LVLA) techniques).
Primary analyses
We examined the effect of SMT compared with recommended therapies, non-recommended therapies, sham (placebo) SMT, and SMT as adjuvant therapy to any other therapy. Sham SMT was any comparator in which SMT involved hand contact, active or passive range of motion, or both, and techniques that simulated SMT but was designed not to deliver a therapeutic effect (eg, light touch or diminished therapeutic force), or even improper care (eg, improper patient positioning or purposely misdirected movements).
Secondary analyses
Although we considered the effect of HVLA SMT versus LVLA SMT (ie, manipulation versus mobilisation) as secondary because it was not included in our protocol, we included this comparison as it represents a point of continued discussion.
We based the determination of recommended and non-recommended interventions on recent international low back pain guidelines from the United States,3 United Kingdom,5 and Netherlands.4 An intervention was categorised into recommended or non-recommended when this was stated in two or more of these guidelines. The recommended control therapies examined in this review included non-drug (eg, exercise) and drug treatments (eg, non-steroidal anti-inflammatory drugs, analgesics), whereas non-recommended interventions included non-effective (eg, light soft tissue massage, no treatment, waiting list control) or potentially even harmful treatments (eg, electrotherapies). When evidence conflicted, or the recommendation was not clear from these guidelines (eg, acupuncture), we consulted other guidelines, such as the COST B13 European guidelines.2
Outcome measures
The primary outcomes were pain intensity and back pain specific functional status. Adverse events and serious adverse events are summarised narratively.
Search methods for identification of studies
We identified randomised controlled trials from an electronic search of several databases (up to 4 May 2018): Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Medline In-Process and Other Non-Indexed Citations, Embase, CINAHL, Physiotherapy Evidence Database (PEDro), Index to Chiropractic Literature, and PubMed. An experienced information specialist carried out the searches according to the recommendations of the Cochrane Handbook.21 In addition, we also screened the reference lists of all included studies and systematic reviews; searched trial registers, specifically, ClinicalTrials.gov and World Health Organization International Clinical Trials Registry Platform (ICTRP); and we sent our selection of studies to trial authors and specialists in SMT to identify any trials potentially missed. Appendix 1 shows the search terms and strategies.
Data collection and analysis
Two review authors (SMR, AdeZ) independently screened the titles and abstracts, evaluated the risk of bias, extracted data, and assessed the quality of the evidence (GRADE). Consensus was reached during meetings. Potentially relevant studies were obtained in full text and independently assessed for inclusion. Only full papers were evaluated. No language restrictions were applied.
Data extraction and management—A standardised form was used to extract the study design (randomised controlled trial), study and population characteristics, intervention and control characteristics, outcome measures, and follow-up intervals, as well other relevant data, such as source of funding, authors’ declaration of interests, and risk of bias. Final value scores (means and standard deviations) were extracted for the meta-analyses. Change scores were converted into a mean value.
Assessment of risk of bias in included studies—risk of bias was assessed according to the 13 criteria recommended by the Cochrane Back and Neck Review Group (see appendix 2). This tool is the same as that recommended by the Cochrane Collaboration, with the addition of items thought to be relevant in the assessment of non-drug trials, such as compliance, use of co-interventions, similarities of the groups at baseline, use of intention-to-treat analysis, and “other” (eg, potential conflicts of interest). We used this tool to evaluate selection bias, performance bias, detection bias, attrition bias, selective outcome reporting bias, and any other forms of bias, such as conflicts of interest. These criteria were scored as low risk, high risk, or unclear risk. Studies with fatal flaws were excluded from the meta-analyses, defined as studies with an exceedingly large drop-out rate or with statistically and clinically relevant important baseline differences, suggesting possibly improper randomisation or selective exclusion of data.
Measures of treatment effect—Pain is expressed as mean difference and functional status as a standardised mean difference (SMD), including 95% confidence intervals. All pain scales were converted to a 100 point scale. A negative effect size indicates that SMT is more beneficial than the comparison therapy; meaning that participants have less pain or better functional status. A random effects model was used for all analyses based on the DerSimonian and Laird approach.22 Analyses were conducted in Review Manager 5.3.
Time and predication intervals—Outcomes were assessed at 1, 3, 6, and 12 months post-randomisation, and data were analysed according to the time closest to these intervals. The primary outcomes were defined as short term (one month), intermediate term (six months), and long term (12 months). We extracted the three month data for meta-analyses but these are not reported here. Additionally, we calculated prediction intervals for the outcomes. These intervals represent the expected range of true effects in similar studies and reflect the variation in treatment effects over different settings, including what effect is to be expected in a future trial.23
Assessment of clinical relevance—Clinical relevance was defined as small: mean difference <10% of the scale (eg, <10 mm on a 100 mm visual analogue scale) or SMD ≤0.5; medium: mean difference 10-20% of the scale or SMD ranging from 0.5 to 0.8; large: mean difference >20% of the scale or SMD ≥0.8. The determination of clinical relevance originates from the behavioural sciences.24 These three levels are broadly used across systematic reviews and are recommended by the Cochrane Back and Neck Review Group, which included consumer/patient representatives.25
Unit of analysis issues—When multiple contrasts from the same trial were examined in the same comparison, we halved the number of participants in the shared comparison. This step accounts from problems arising when multiple arms from the same trial are examined in the same meta-analysis. “Halving” the number of participants corrects for error introduced by double counting.21
Dealing with missing data—When it was not possible to extract metadata from a publication, we used individual patient data if available. The research team has received these data from most studies published since 2000 for an individual patient data meta-analysis that we are currently conducting. In all other cases, we attempted to contact the author if data were missing. If no response was received, we followed the guidelines as outlined in the Cochrane Handbook (section 7.7.3).21
Assessment of reporting biases—Funnel plots were constructed, where possible, to explore publication bias. Additionally, we examined potential conflicts of interest as well as the funding source.
Data synthesis—GRADE was used to evaluate the overall quality of the evidence for each outcome, which ranges from high to very low quality and is based on five domains: limitations of design, inconsistency of results, indirectness, imprecision, and other factors, such as publication bias. Appendix 3 describes the criteria and operational definitions.
Assessment and investigation of heterogeneity—A prerequisite to pooling data was based on clinical homogeneity, which is why we stratified the meta-analyses by type of comparison, outcome, and time interval. Statistical heterogeneity was examined by inspecting the Forest plot and was formally tested using the Q test (χ2) and I2. We attempted to explain cases of considerable heterogeneity (defined as an I2 statistic ≥75%) using meta-regression for those comparisons with sufficient data. The following variables were considered a priori: duration of the low back pain (subacute or chronic versus exclusively chronic), type of clinician (chiropractor versus other), type of radiating pain (above knee versus below knee); multimodal SMT (ie, SMT delivered alone compared with examined in a larger, multimodal context or as a package of care), and type of technique (HVLA versus LVLA). After examining the discriminative ability of these variables, we considered the additional variable of country where the study was conducted. Ultimately, we modelled just four variables: duration of the low back pain, type of clinician, multimodal SMT, and country. In the first step we conducted a univariate analysis and in a subsequent step we used the two variables showing the strongest effect to construct the final model. We report the effect and I2 for the final models only. These analyses were conducted in STATA, version 14.1.
Sensitivity analyses—Sensitivity analyses were planned a priori to determine the robustness of the data for risk of bias items (selection bias, performance bias, attrition bias, and selective outcome reporting bias), and by type of contrast (SMT versus exercise therapy). Among the risk of bias items we focused on selection bias, specifically treatment allocation, because this criterion showed exaggerated intervention effect estimates in a meta-analysis, which included a large collection of randomised trials published in the Cochrane Library.26
Patient and public involvement
No public or patient representatives were directly involved in the draft or process of this review. However, the primary outcomes examined in this review represent a core set recommended for low back pain, which included patient representatives in its development.
Results
In total, 47 trials fulfilled the inclusion criteria, 21 of which were not included in the previous review (fig 1).1427282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172
Included studies
The countries in which the studies were conducted varied. Fifteen studies were conducted in the United States,142829333440414445464954667072 seven in the United Kingdom,32353839506973 three each in Finland,425271 Australia,365167 and Italy,315565 two each in Sweden,5761 Denmark,5356 Egypt,5860 and India,5964 and one each in Belgium,43 Spain,30 Switzerland,27 the Netherlands,47 Greece,48 Turkey,63 Pakistan,68 and Tunisia.37 All trials were published in English except the trial conducted in Tunisia, which was published in French. A detailed description of the characteristics of the included studies is available on request from the primary author. In total, 9211 patients were examined. Study sample sizes ranged from 21 to 1334 (median 132, interquartile range 64-240).
Study population
Most studies included middle aged participants (on average, 35-60 years of age) with or without radiating pain. Less than half of the studies examined those with exclusively chronic low back pain273031323436394041484950515658596364656972; however, among those studies that recruited a mixed population, the duration of the pain typically ranged from months to years (see table A in appendix 5). None of the studies made a clear distinction between persistent low back pain or exacerbation of a chronic condition.
Provenance of evidence
We would have liked to have described whether the research team was multidisciplinary and whether it included clinicians who were involved in the treatment, but in many cases these data were not reported. Importantly, no official disclosure was reported in most of the studies, although many were older studies for which disclosure was not standard procedure at the time.
Primary investigators
Affiliations—The primary investigators were affiliated with a department of physiotherapy or osteopathy within a university setting,14273033364957585963646572 health sciences department or similar within a university setting,2941434647485152535461626771 department of medicine, rheumatology, or similar,3537385055566068 chiropractic based research department,28344044456670 or clinician initiated (independent of a university or college)3132394269
Qualifications—The primary investigators (excluding potential training as a researcher, PhD) were trained as chiropractor,2829344041444546516769 physical/manual therapist,143033364352535768 osteopath,4972 medical doctor,31353738425055606271 or naturopathist,61 and some had no training as therapist or clinician3947545970 or qualifications were unknown or unclear.273248565863646566
Involvement in treatment—In four studies the primary investigator was involved in treatment,14435268 in nine not involved,2728293031333435363839404142444546474950535455616263666770717273 and in the remainder it was unknown or unclear.323748515657585960646569
Funding and competing interests
Fifteen of the studies were funded by government,272930323841424447505162636970 12 by a private or professional organisation,283139495354555657666771 and eight by a combination of these.1434364045466172 In 12 studies funding was not reported or was unclear.333537434852585960646568
In 16 studies the authors declared no competing interests,14272930313441434853606162676870 and in the remainder no official disclosure was reported28323335363739404244454647495051525455565758596364656669717274
Types of technique and practitioner
Practitioners—In 16 studies treatment was delivered by a chiropractor,28293440414445465153545566676970 in 14 by a manual or physical therapist,2730333639434748505758596364 in six by a medical manipulator or orthomanual therapist,313552566068 in five by an osteopath,3238496572 in two by a bonesetter,4271 in one by a naprapath,61 and in one by several different disciplines.73 In another study, it was unclear what type of SMT treatment was delivered or the level or skill of the treating clinicians.37 In virtually all studies, experienced clinicians or therapists delivered the treatment, with the exception of one study where treatment was delivered by a few predoctoral osteopathic fellows.49
Techniques—Three types of primary technique were used in the SMT arm of the studies: high velocity, low amplitude (HVLA) thrust SMT,142829333544455051535455565960656670 low velocity, low amplitude (LVLA) passive movement techniques,334042434448575864687071 or a combination (HVLA manipulation and LVLA mobilisation).2730313234363839414647495253616263656972 In one study, the technique used was unclear,37 and in four studies, HVLA SMT was compared with LVLA SMT.30334470
Risk of bias in included studies
Three studies were identified as having a major flaw and were excluded from the meta-analyses.323951 Less than half of the studies (45% (n=21/47)) used both an adequate sequence generation and an adequate allocation procedure.272829303134364041424447536163676970717375 Five studies (10% (n=5/47)) attempted to blind patients to the assigned intervention by providing a sham treatment,3749606672 while in one study it was unclear.58 More than half of the studies (57% (n=27/47)) provided an adequate overview of withdrawals or drop-outs and kept these to a minimum.142729303133343536373841424345474854596165676970717275 Less than one third of the studies (30% (n=14/47)) published or registered the protocol, and the reported outcomes were consistent with the protocol.1429303641434448536162637172 Appendix 4 summarises the risk of bias assessments.
Effects of interventions
Table 1 summarises the treatment effects and quality of the evidence for all comparisons.
Summary of treatment effects and GRADE summary of findings for all comparisons among trials included in systematic review of spinal manipulative therapy (SMT) for chronic low back pain
Primary analyses
SMT versus recommended interventions
Twenty six studies compared the effects of SMT with recommended interventions.2829313234363940424445474851525355575961626368697175 Data could not be extracted from five studies,3239475155 three of which had a major flaw.
Pain—Moderate quality evidence suggested that SMT is not statistically better than recommended interventions at one month and 12 months, although the difference was significant at six months. The size of the effect was, however, not clinically relevant (fig 2). Exclusion of extreme outliers accounted for a large percentage of the statistical heterogeneity for this outcome at one month (mean difference −0.39, 95% confidence interval −2.41 to 1.62; participants=3005; studies=23; I2=44%), while the overall effect remained virtually unchanged.
Mean difference in reduction of pain at 1, 3, 6, and 12 months (0-100; 0=no pain, 100 maximum pain) for spinal manipulative therapy (SMT) versus recommended therapies in review of the effects of SMT for chronic low back pain. Pooled mean differences calculated by DerSimonian-Laird random effects model. See supplementary file for more detailed graphic
Back specific functional status—Moderate quality evidence suggested that SMT results in a small, statistically better effect than recommended interventions at one month but not statistically better effect at six and 12 months (fig 3). Exclusion of extreme outliers accounted for a large percentage of the statistical heterogeneity for this outcome at one month (SMD −0.12, 95% confidence interval −0.23 to −0.01; participants=2907; studies=22; I2=44%), while the overall effect remained virtually unchanged.
Standardised mean difference for improvement in function at 1, 3, 6, and 12 months for spinal manipulative therapy (SMT) versus recommended therapies in review of the effects of SMT for chronic low back pain. Pooled standardised mean differences calculated by DerSimonian-Laird random effects model. See supplementary file for more detailed graphic
SMT versus non-recommended interventions
Eleven studies compared the effects of SMT with non-recommended interventions.1427384145475054556770 Data could not be extracted from three studies.475455
Pain—High quality evidence suggested that SMT results in a small, statistically significant but not clinically better effect than non-recommended interventions at one month. Moderate quality evidence suggested that SMT results in a statistically significant but not clinically better effect at six months, and low quality evidence that SMT results in a statistically significant but not clinically better effect at 12 months (fig A in appendix 5).
Back specific functional status—High quality evidence suggested that SMT results in a small to moderate statistically and clinically better effect than non-recommended interventions at one month. Moderate quality evidence suggested that SMT results in a small, statistically significant and clinically better effect at six months, and low quality evidence that SMT results in a small to moderate, statistically significant and clinically better effect at 12 months (fig B in appendix 5).
SMT versus sham SMT
Seven studies compared the effect of SMT with sham SMT.14374349606672
Pain—Low quality evidence suggested that SMT does not result in a statistically better effect than sham SMT at one month. Exclusion of an extreme outlier accounted for a large percentage of the statistical heterogeneity for this outcome at this time interval (mean difference −3.49, 95% confidence interval −6.03 to −0.94; participants=781; studies=9; I2=5%), while the overall effect remained virtually unchanged. Additionally, very low quality evidence suggested that SMT does not result in a statistically better effect than sham SMT at six and 12 months (fig C in appendix 5).
Back specific functional status—Low quality evidence suggested that SMT results in a moderate to strong statistically significant and clinically better effect than sham SMT at one month. Exclusion of an extreme outlier accounted for a large percentage of the statistical heterogeneity for this outcome at this time interval (SMD −0.27, 95% confidence interval −0.52 to −0.02; participants=698; studies=7; I2=39%), resulting in a small, clinically better effect in favour of SMT. Additionally, very low quality evidence suggested that SMT does not result in a statistically significant better effect than sham SMT at six and 12 months (fig D in appendix 5).
SMT as adjuvant therapy
Seven studies examined the adjuvant effects of SMT when combined with other therapies.35454956646573
Pain—Moderate quality evidence suggested that SMT results in a small, statistically significant but not clinically better effect at one month and 12 months, and low quality evidence that SMT does not result in a statistically better effect as an adjuvant therapy at six months (fig E in appendix 5).
Back specific functional status—Moderate quality evidence suggested that SMT results in a small, statistically significant and clinically better effect at one month, and low quality evidence that SMT results in a small, statistically significant and clinically better effect at 12 months, but not statistically significant effect at six months (fig F in appendix 5).
Secondary analyses
HVLA SMT versus LVLA SMT—Four studies examined the effect of HVLA SMT versus LVLA SMT.30334470 We found no statistically significant difference in effect between either technique for pain relief or improvement in function at one month (judged to be moderate and low quality, respectively). The evidence at six months was of low quality and there were no data for 12 months.
Mobilisation versus mobilisation—One small study with a high risk of bias for many criteria compared the effects of Maitland mobilisation with Mulligan mobilisation.58 The authors concluded that there was no significant difference between either technique for the short term reduction of pain.
Prediction intervals—Prediction intervals for the effect of SMT versus recommended therapies suggested a small to moderate effect in favour of either therapy, meaning that the therapy chosen by patients and clinicians should be based on factors other than effectiveness alone. Data were too few for the other comparisons to ascribe a meaningful interpretation to those results (table B in appendix 5).
Explanation of statistical heterogeneity and sensitivity analyses
We conducted meta-regression only for the comparison of SMT with recommended therapies. In general, two variables were typically included in the final model: multimodal SMT and duration of the low back pain (tables C and D in appendix 5). However, these variables did not explain the statistical heterogeneity for short term outcomes, and marginally for intermediate and long term outcomes. The moderator effects were also typically small and not clinically relevant. This meant that there was appreciably no difference in effect when SMT was offered as a package of care (as opposed to SMT alone) or when patients with exclusively chronic low back pain were included (as opposed to a mixed population). Meta-regression was not conducted for the other comparisons because data were too few to ascribe any meaningful interpretation to those results. Additionally, no appreciable difference was found in effects for risk of bias or when the effect of SMT versus exercise was examined.
Publication bias—Publication bias was only examined for SMT versus recommended therapies, owing to the paucity of data for the other comparisons. We constructed two separate funnels plots for pain and functional status for all time measurements (figs G and H in appendix 5). Although these funnel plots do not suggest publication bias, this cannot be ruled out.
Adverse events
About half of the studies examined adverse events (table 2).2728293031333435364041434445515660616267707172 In most of these studies it was unclear how and whether adverse events were registered systematically29303334616267; therefore, these data might be unreliable and not accurate for incidence. However, one of the studies included in this review67 was a secondary analysis of a trial designed to examine the incidence of these events.76 That study (n=183) suggested no increased risk of an adverse event (relative risk 1.24, 95% confidence interval 0.85 to 1.81) or severe adverse event (1.9, 0.98 to 3.99) compared with sham SMT.76 Two studies reported serious adverse events3472: in one the Data Safety Monitoring Board judged none of these events to be associated with SMT,34 and in the other the Data Safety Monitoring Board judged one event to be possibly related to SMT.72
Summary of adverse event assessments among trials included in systematic review of spinal manipulative therapy (SMT) for chronic low back pain
Discussion
In the treatment of chronic low back pain in adults, moderate quality evidence suggests that spinal manipulative therapy (SMT) results in similar outcomes to recommended therapies for short, intermediate, and long term pain relief as well as improvement in function. In addition, the quality of evidence varied suggesting that SMT does not result in clinically better effects for pain relief but does result in clinically better short term improvement in function compared with non-recommended therapies, or sham, and when included as an adjuvant therapy.
Most studies examined the effect of SMT in a pragmatic setting and might therefore be considered the most robust evidence. Given the considerable data available, we can now calculate within reasonable certainty the effect of SMT in this setting as well as the impact of a future, methodologically well conducted trial (as determined by the prediction intervals). Evidence for the remaining comparators was considered to be of moderate quality or lower (with the exception of the short term effect of SMT versus non-recommended therapies), suggesting some uncertainty around these effect estimates. However, it is questionable whether additional studies are necessary, and it is debatable whether studies that examine the effect of SMT compared with non-recommended therapies or sham (placebo) therapies will add further to our understanding. In fact, during this update we identified several, recent small pragmatic studies with a high risk of bias.4858596368 This is of concern because these types of studies only weaken rather than strengthen the evidence and should be discouraged. Curiously, this finding contrasts with an earlier study that identified a trend towards better quality studies investigating SMT.77 Future studies should focus on identifying moderators likely to influence treatment effects (such as socioeconomic status, level of education), and this is a line of evidence that we are currently pursuing in an individual participant data meta-analysis.
We present average clinical effects for the groups. For a better interpretation of the results, benefit might arise if additional analyses are included in future trials, such as the proportion of patients achieving a clinically meaningful response. This could be obscured by group averages. Additionally, we can better interpret the effects if greater attention is paid to the qualitative components of interventions, such as the context of the visit, and patient beliefs and preferences.78
Comparison with other studies
Ostensibly, these results are consistent with our previous review.19 One major difference between the reviews was the classification of the comparator: in the first review we classified therapies into effective and non-effective, whereas in this review we classified them into recommended and non-recommended therapies. It was thought that this would best help the translation of findings to clinical practice. We based the classification of the comparator on recent guidelines, but this was not always clear because evidence among the different guidelines conflicted (eg, acupuncture), or a given therapy was not classified (eg, back school). We examined the impact of classifying these therapies with their opposing comparator in sensitivity analyses (data not shown), and this did not affect our results. Furthermore, our results are consistent with other recently published high quality systematic reviews798081 and guidelines that recommend SMT.235
Implications for clinicians
SMT can be delivered as a standalone therapy, although it is typically offered within the constructs of a broader treatment package, together with exercise therapy or combined with usual care, as is recommended in recent national guidelines for low back pain.582 This is important because SMT is by nature a passive treatment. Therefore, to prevent inappropriate behaviour and to empower patients to take control of their condition it is vital that practitioners impart the proper message to their patients.
The incidence of adverse events and serious adverse events based on the studies included here are difficult to assess because less than half of the randomised controlled trials examined these, and in most of the studies the methodology was unclear. Importantly, given the low incidence of serious adverse events, randomised controlled trials are not the design of choice. Based on a recent systematic review, serious adverse events after SMT for low back pain are thought to be rare and include case reports of cauda equina syndrome, fractures, and neurological or vascular compromise.83 A recent comprehensive scoping review, which examined the risks of manual treatments to the spine, identified 250 articles in which serious adverse events were reported. Most of these focused on adverse events after treatment to the neck.84 The body of evidence, which includes data from large, prospective observational studies of SMT, suggests that benign adverse events are common and serious adverse events are rare. The incidence and causal relations with serious adverse events are difficult to establish, in part due to inherent methodological limitations of the included studies. Importantly, predictors of these events are unclear. Given this, clinicians should ensure that patients are fully informed of potential risks before treatment.
Implications for policy makers and other researchers
Although we focused on the effects of SMT in this review, the costs associated with care should also be considered. The most recent systematic review on cost effectiveness of non-invasive and non-drug interventions for the treatment of low back pain concluded that manual treatments, including SMT and massage, should be considered a cost effective option.85 This conclusion, however, was based on 10 studies, only two of which are included in this review.7386 Another recent systematic review that focused on the effects of SMT for spinal pain concluded that SMT is a cost effective option when used alone or in combination with other treatments.87 However, this conclusion was based on six studies, including studies that examined the effect of SMT for the treatment of neck pain, and was limited to the same two studies cited previously. 7386 To our knowledge, no other economic evaluations have been done of SMT for the treatment of chronic low back pain. Although we did not actively search for these types of evaluations because that was an objective of this review, it is unlikely we missed any economic evaluations in these studies. The primary author knows this literature well and regularly attends meetings in which trial results are presented. Furthermore, it is likely that studies as well as protocols would have referenced an economic evaluation if it existed. Therefore, it remains to be determined whether SMT is a cost effective option for the treatment of chronic low back pain.
Limitations of this study
The most important limitations are those inherent to most (if not all) systematic reviews—namely, the limited number of studies with a low risk of bias, as well as ambiguity about the impact of publication bias. Furthermore, we could not resolve the problem related to statistical heterogeneity nor is this likely to be resolved in future reviews: studies of SMT are conducted in varied settings, among different populations, using several methods of recruitment and SMT techniques that are subsequently compared with various types of therapies. Finally, in most studies it was unclear if the research team was multidisciplinary, and whether it included clinicians involved in the treatment of patients, but perhaps most importantly, given that disclosure was often not reported, potential conflicts of interest cannot be ruled out.
Recommendations for future study
Future trials of SMT for low back pain should include an economic evaluation; an analysis of the proportion of patients who achieved a specified level of pain relief (eg, percentage of those experiencing 50% pain improvement); a better description of the qualitative components of SMT, such as the context of the visit, patient beliefs, and preferences, and also quantitative components, such as factors that are likely to influence treatment.
The evidence suggests that SMT results in a modest, average clinical effect at best: future trials on the effect of SMT for chronic low back pain are not necessary, unless they contain a novel approach, are well conducted, and address any of these specific recommendations.
Private or governmental agencies should refrain from funding small trials that are poorly conceived.
Conclusions
SMT produces similar effects to recommended therapies for chronic low back pain but results in clinically better effects for short term improvement in function compared with non-recommended therapies, sham therapy, or when added as an adjuvant therapy. Clinicians should inform their patients of the potential risks of adverse events associated with SMT.
What is already known on this topic
Numerous randomised controlled trials of varying methodological quality and size have examined the benefits and harms of spinal manipulative therapy (SMT) for the treatment of chronic low back pain
These trials have been summarised in numerous systematic reviews with varying results
SMT is not currently recommended as a first line treatment for chronic low back pain and its effects are uncertain
What this study adds
SMT has similar effects to recommended therapies for chronic low back pain, although it seems to be better for short term improvement in function
Data for the other comparisons (placebo SMT and SMT as adjuvant therapy) might be considered less robust and therefore unclear
Information is limited on the incidence of adverse events and serious adverse events with SMT for this population
Acknowledgments
We thank the editorial board of the Cochrane Back and Neck Review Group for its constructive comments, particularly Shireen Harbin, and those authors who provided clarification of their trials for this update.
Systematic review registration: A protocol of this review is registered with the Cochrane Library. Rubinstein SM, van Middelkoop M, Assendelft WJJ, de Boer M, van Tulder MW. Spinal manipulative therapy for chronic low-back pain. Cochrane Database Syst Rev 2009(4):CD008112; doi:10.1002/14651858.CD008112.
Footnotes
Contributors: SMR, MWvT, and WJJA conceived and designed the study. SMR, AdeZ, MRdeB, and MWvT analysed and interpreted the data. SMR, AdeZ, and MWvT drafted the review. All authors critically revised the article for important intellectual content and gave final approval for the article. MRdeB provided statistical expertise. SMR provided administrative, technical, and logistical support. SMR, AdeZ, and MvM (2011 publication) and MRdeB and WJJA (2004 publication) collected and assembled the data. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.
Funding: None.
Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: SMR received personal grants from the European Chiropractors’ Union (ECU), the European Centre for Chiropractic Research Excellence (ECCRE), the Belgian Chiropractic Association (BVC) and the Netherlands Chiropractic Association (NCA) for his position at the Vrije Universiteit Amsterdam. He also received funding for a research project on chiropractic care for the elderly from the European Centre for Chiropractic Research and Excellence (ECCRE). AdeZ received a grant from the European Chiropractors’ Union (ECU) (grant No A14.03), for an independent study on the effects of SMT. SMR and AdeZ declare that they work in their own private clinics as chiropractors. The remaining authors received no support from any organisation for the submitted work; have no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and have no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: Not required.
Data sharing: Details of the characteristics of the included studies are available from the corresponding author at s.m.rubinstein@vu.nl.
Transparency: All authors affirm that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.
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