Introduction
Primary and early prevention
Primary prevention in chiropractic practice
Challenging the subluxation model
The duty to test non-plausible clinical activities
Confidence in poor quality research
Pedagogic dimension
Objectives
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For which physical, non-musculoskeletal diseases has the effect/benefit of chiropractic treatment been studied in the chiropractic literature?
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Which study designs have been used?
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Were the designs appropriate to uncover effect of intervention?
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Was the basic methodological quality sufficient to make results credible?
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What evidence is there that chiropractic treatment can prevent disease or stop it in its early stage?
Method
Identifying relevant studies
Journal/Online library | Search terms, issues and reference list used | Date of the last search | # articles included/# total articles |
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PubMed | (chiropract* OR subluxat* OR ‘manual therapy’ OR ‘spinal manipulation’ OR ‘spinal manipulative’) AND (prevent* OR wellness OR disease OR mortality OR morbidity) | 04/10/2017 | 5 / 8628 |
Embase | (chiropract* OR subluxat* OR ‘manual therapy’ OR ‘spinal manipulation’ OR ‘spinal manipulative’) AND (prevent* OR wellness OR disease OR mortality OR morbidity) [embase]/lim not [medline]/ lim) | 29/09/2017 | 1 / 2774 |
Index Chiropractic Literature (ICL) | Prevention (search 1) | 07/10/2017 | 0 / 535 |
Wellness (search 2) | 07/10/2017 | 1 / 199 | |
Journal of Chiropractic Medicine (JCM) |
All the issues from inception to 2017 were screened.
| 07/10/2017 | 2 / 486a |
Journal of Vertebral Subluxation Research (JVSR) |
All the issues from inception to 2017 were screened.
| 07/10/2017 | 8 / 351a |
Functional Neurology, Rehabilitation, and Ergonomics (FNRE) |
All the issues from inception to 2017 were screened.
| 07/10/2017 | 0 / 126a |
Hannon [8] | Reference list of the article:
Hannon SM. Objective Physiologic Changes and Associated Health Benefits of Chiropractic Adjustments in Asymptomatic Subjects: A Review of the Literature. J. Vertebral Subluxation Res. 2004.
| NA | 3 / 65 |
Article selection
Inclusion criteria
Exclusion criteria
Charting the data
Checklists
First Author (Year) Journal Affiliation Country | Research question(s) or purpose of study | Type of manipulative therapy/chiropractic treatment | Outcome variables for studied condition | Authors’/author’s conclusion in relation to effect/benefit of chiropractic treatment |
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Kessinger (1997) JVSR ? USA | “to assess the influence of upper cervical adjustments on pulmonary function.” | Upper cervical treatment | Lung function: a)forced vital capacity (FVC); b)forced expiratory volume in one second (FEV-1) | “The study indicates that subjects show improved pulmonary function in FVC and FEV-1 after receiving chiropractic care for the correction of upper cervical vertebral subluxation.” |
Kessinger (1998) JVSR ? USA | “to investigate the relationship between frequency of adjustments (hence presence of a vertebral subluxation) and changes in visual acuity among a population of subjects previously naïve to any form of chiropractic.” | “Upper Cervical Specific Care for the correction of atlas and/or axis (C-1, C-2)” | Distance visual acuity | “This information suggests that correction of upper cervical subluxation, regardless of its vector character (right versus left, or inferior or superior to axis) is associated with either uni-lateral, and/or bilateral improvements in %DVA.” “Thus, through the upper cervical adjustment procedures employed in the present study, improvement in visual acuity appears to be linked to correction of vertebral subluxation.” “Consequently, while further study of other subject populations is required to validate the preliminary findings presented in this article, it appears that the effects observed are of longer term than would be expected from a stimulus-response reaction. Further evaluation, however, will be needed to elucidate the long term nature of the effects observed, as well as to decipher the differential vision changes apparent in the present study.”
DVA = Distance Visual Acuity
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Morter (1998) JVSR Morter Health System, Inc. and developer of Bio-Energetic Synchroniza-tion Technique USA | Testing the hypothesis that “lower salivary pH would accompany excessive sympathetic stimulation while higher pH values would accompany parasympathetic predominance”. Also to test the hypothesis that “salivary pH values would increase or decrease accordingly after administration of care”. | Bio-energetic synchronization which “updates or re-sets engrams eliciting inappropriate physiology often associated with autonomic imbalance” | Salivary pH | “Effect sizes for the two groups revealed a large treatment effect in the S-Group (0.80) compared to a moderate effect in the P-Group (0.50) …”
S-Group = sympathetic group
P-Group = sympathetic group
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Campbell (2005) JVSR Camgen, Inc. USA | “to assess the effect of short-term and long-term chiropractic care on serum thiol levels in asymptomatic subjects”
Thiol = a surrogate estimate of human health status; of DNA repair enzyme activity
| -network spinal analysis -diversified technique with drop-table -activator methods | Plasm/serum thiol | “Asymptomatic or primary wellness subjects under chiropractic care demonstrated higher mean serum thiol levels than patients with active disease and produced some values that were higher than normal wellness values.” “chiropractic could influence the basic physiological process of endogenous generation of oxidative stress” |
Boone (2006) JVSR Sherman College of Straight Chiropractic USA | Pilot study “to gather preliminary information regarding chiropractic care and possible links to immune status and improved aspects of health and quality of life” | -“chiropractic care” -“chiropractic adjustments when indicated” | Blood tests for immunological markers | “This pilot study has provided some preliminary information regarding chiropractic care and possible links to immune status …” |
McMasters (2013) Journal of Chiropractic Medicine Private practice USA | “to determine if a course of chiropractic care would change BP measurements in African American patients and to determine if a study was feasible in a chiropractic teaching clinic.”
BP = blood pressure
| “chiropractic adjustments (manipulation) based upon the spinal examination findings” | Systolic and diastolic blood pressure on subjects diagnosed with prehypertension or stage 1 hypertension | “There was no statistically significant difference in BP following chiropractic care for this group of African American patients. However, when 4 patients who had large BMIs (outliers) were excluded from the group, a statistically significant decrease in diastolic BP was observed. It is possible that patients with higher BMI may be more resistant to BP reductions in the context of chiropractic care. Unfortunately, the mechanism between BMI and BP is not well understood.”
BMI=Body Mass Index
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Jones (2014) Disability and Rehabilitation School of Health Science and Social Care UK | “to investigate the hypothesis that MT produces additional benefit when compared with breathing retraining alone in a group of patients with primary DB.”
MT = Manual Therapy
DB = Dysfunctional breathing
| All the subjects were treated with standardised respiratory physiotherapy management The intervention group: individualised selection of manual therapy techniques (e.g. Maitland mobilisation/ manipulation) |
Primary outcome
-Nijmegen score for dysfunctional breathing
Secondary outcome
-Spirometry measured by: a)forced expiratory volume in one second (FEV1) b)forced vital capacity (FVC); -Breath hold time | “There was no significant difference between the manual therapy and respiratory treatment groups for the primary outcome (Nijmgen score) or any secondary outcomes” |
Goertz (2016) JMPT Palmer college of Chiropractic USA | Pilot study “to estimate the treatment effect and safety of toggle recoil spinal manipulation for blood pressure management” | Toggle recoil spinal manipulation therapy | Systolic and diastolic blood pressure on subjects diagnosed with prehypertension or stage 1 hypertension | “...there is limited research to support the use of SMT for patients with high BP. Thus, rigorous studies to evaluate the efficacy and safety of SMT for hypertension are needed to guide chiropractic clinical practice.”
BP=Blood Pressure
SMT = Spinal Manipulative Therapy
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First Author (Year) Journal Affiliation Country | Methodological considerations | Were differences between groups tested for statistical significance in relation to effect/benefit of treatment? | Comments by reviewers in relation to major methodological improvements needed to test effect/benefit of intervention | ||||
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Design | Comparison with non-treated (placebo) group or an otherwise treated group? | Random and concealed allocation to treatment groups | Main outcome variable(s) validated in some way? (reproducible/reliable) | Assessor blinded to treatment group? | |||
Kessinger (1997) JVSR ? USA | Prospective outcome study of lung function after 2 weeks of chiropractic care | No placebo or control group | NA because no control group | FEV-1 reported to be most reproducible of the two measurements with ref. provided but level of reproducibility not reported | NA There was only one group | NA There was only one treatment group | To test the effect on pulmonary function after chiropractic care of the neck, one could a) either compare it to a sham treatment, or to b) another type of treatment known to be effective or (possibly) to c) a treatment elsewhere in the spine, if the purpose is to see if the ‘neck’ is important. |
Kessinger (1998) JVSR ? USA | Prospective outcome study of visual acuity after six weeks of chiropractic. Also the dose of treatment was studied. | No placebo or control group | NA because no control group | Not reported but used standard eye chart | NA There was only one group | NA There was only one treatment group | To test if the ‘dose’ of adjustments matter, patients should at baseline be randomly allocated into one of several groups each receiving different numbers of treatments/adjustment. |
Morter (1998) JVSR Morter Health System, Inc. and developer of Bio-Energetic Synchronization Technique USA | Prospective outcome study of salivary pH in two groups defined as predominantly sympathetic or parasympathetic after 4-days of chiropractic treatment | No placebo or control group but patients were all treated in the same way and outcomes were compared in relation to whether they predominantly were sympathetic or parasympathetic | NA because study sample stratified on predetermined criteria | Not reported but used standard pH paper | NA There was only one group | NA There was only one treatment group | To establish if different subgroups react differently to the chiropractic treatment, then the groups could either a) be tested for outcome in a randomized controlled clinical trial design or (possibly) b) be tested for outcome in a sufficiently large non-controlled prospective outcome study that allows for subgroup analyses. The diagnosis of predominantly sympathetic and parasympathetic subjects must be valid and/or reproducible. The assessment should be done with valid/reproducible methods by assessors that are blinded to classification group. |
Campbell (2005) JVSR Camgen, Inc. USA | A retrospective study comparing serum thiol levels in patients with active disease (? Abstract)/apparently disease free (? Materials and Methods) for two groups (? Materials and Methods) or perhaps three groups (? Table 1). These groups had been treated with chiropractic care for a) less than one year or b) at least one year. Perhaps there was also a third non-symptomatic apparently healthy control group (? Table 1). | Perhaps, not clear | No | Serum thiols claimed to be valid as indicators for mortality and active disease | NA There was only one group | Yes | To test if chiropractic care and dose of care can affect DNA repair then a study sample should have been randomly divided into treated and untreated, and this could have been done for different study populations, the sick and the healthy. The dose-response should be tested in a similar way, i.e. a group of patients receiving short-term and one long-term treatment in a random fashion. The results in this study relate only to association and not effect. The claim that “results clearly support” etc. are unfounded. |
Boone (2006) JVSR Sherman College of Straight Chiropractic USA | Prospective outcome study of immune status and health after three and nine months of chiropractic care | NA because no control group | NA because no control group | Not reported | NA There was only one group | NA There was only one treatment group | Just because a study sample is small, does not justify to call it a ‘pilot study’. A pilot study should be used to test study procedures, ability to obtain patients, etc. To draw any (even preliminary) conclusions on effect/benefits of treatment, a sham/control treatment is needed. |
McMasters (2013) Journal of Chiropractic Medicine Private practice USA | Prospective outcome study of blood pressure after 21 to 23 chiropractic consultations | NA because no control group | NA because no control group | Probably valid | NA There was only one group | NA There was only one treatment group | As this is a feasibility study, it is not really appropriate to concentrate the discussion on ‘improvement’ but should concentrate more on reasons for/against the possibility to perform a proper randomized controlled trial (RCT). To test the effect of spinal manipulation on blood pressure an RCT with a sham group would be necessary. |
Jones (2014) Disability and Rehabilitation School of Health Science and Social Care UK | 2-arm randomized controlled trial of dysfunctional breathing after 2, 4, 8, 12 and 26 weeks of either a) respiratory management (RM) or b) RM plus manual therapy | Yes, with a control group | Yes | Yes, for the questionnaire. The other variables are frequently used so probably valid. | Yes | Yes | The design is appropriate for testing difference in outcome between treatment groups, in this case to see if manual therapy can provide added benefit to another treatment. |
Goertz (2016) JMPT Palmer college of Chiropractic USA | 2-arm randomized controlled trial of blood pressure after 1, 6 and 12 visits of spinal manipulation | Yes, with a sham group | Yes | Probably valid | Yes | Yes | The design is appropriate for testing whether spinal manipulation has an effect on blood pressure. However, the absence of effect should be discussed more clearly. |
First Author (Year) Journal Affiliation Country | Research question(s) or purpose of study | Design | Study population | Outcome variables | Which factors associated with cause were included? | Authors’/author’s conclusion in relation to effect/benefit of chiropractic treatment |
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Hart [19] (2007) JVSR Sherman College of Straight Chiropractic USA | “to better understand possible mechanisms for the health disparity along the River”
Mississippi River
| Register study | General population from the states along the Mississippi River | Various diseases and mortality | Only correlations between risk factor (physician/chiropractor ratios) and outcomes (various health conditions and death) were studied | “Chiropractors had stronger correlations for improved health outcomes when compared to physicians. Further study is indicated into other possible causative mechanisms such as the quality of drinking water and health care delivery.” |
Hart [20] (2007) Journal of Chiropractic Medicine Sherman College of Straight Chiropractic USA | “This study assesses doctor (allopathic/ osteopathic physician and chiropractor) ratios in the 50 states in the United States and correlates these ratios with various health outcomes to determine if one doctor type has stronger correlations in certain outcomes compared with the other doctor type by geographic region.” | Register study | General population from 50 states in the United states | Various diseases and mortality | Only correlations between risk factor (physician/chiropractor ratios) and outcomes (various health conditions and death) were studied | “Correlation does not necessarily show causation but may provide clues. […] It is possible, although care should be taken to avoid overspeculation, that doctors of chiropractic are having an effect in seemingly unlikely outcomes such as cardiovascular and cancer deaths” |
Hart [21] (2008) JVSR Sherman College of Straight Chiropractic USA | As above (Hart, 2007) [20], but adding the variables of income, education and health insurance coverage in the analysis | Register study | General population from 50 states in the United states + district of Columbia | Various diseases and mortality | Only correlations between risk factor (physician/chiropractor ratios) and outcomes (various health conditions and death) were studied | “Correlation does not necessarily show causation but it can provide clues. Median income, educational attainment, and chiropractor ratios showed the strongest correlation with reduced mortality rates while health insurance and medical doctor ratios showed the weakest correlation with reduced mortality rates.” |
Hart [22] JVSR (2008) JVSR Sherman College of Straight Chiropractic USA | As above (Hart, 2007) [20] but adding the variables of age, income and education in the analysis | Register study | General population from 50 states in the United states + district of Columbia | Various diseases and mortality | Only correlations between risk factor (physician/chiropractor ratios) and outcomes (various health conditions and death) were studied | “The age factor […] had the strongest association with death rates” compared to doctor ratios. “The only statistically significant relationship among doctor ratios was observed with medical doctors and cerebrovascular, though chiropractor ratios showed a stronger average correlation with reduced death rates.” |
Hart [23] International Dose-Response Society (2013) Sherman College of Chiropractic USA | “to simply compare the correlation between DC and MD concentrations (doses) in relation to hypertension mortality rates (responses).”
DC = Doctors of Chiropractic
MD = Medical Doctors
| Register study | General population from district of Columbia (without Alaska and Wyoming) | Hypertension Death rates | Only correlations between risk factor (physician/chiropractor ratios) and outcomes (various health conditions and death) were studied | “DC concentrations (dose) revealed a stronger beneficial correlation with decreased hypertension (essential hypertension and renal hypertensive disease) mortality rates (response) compared to MD concentrations” (Causal inference is not claimed.) |
First Author (Year) Journal Affiliation Country | Representativeness | Definition of chiropractic treatment | Outcome variables validated in some way? | Control for other variables that could have an effect on outcome | Comments by reviewers in relation to major methodological improvements needed to test effect/benefit of intervention | |
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Selection of study subjects (whole population, random selection, convenience sample) | Response/ Non response comparison | |||||
Hart [19] (2007) JVSR Sherman College of Straight Chiropractic USA | Whole population? | Not reported | Chiropractic care not described Presence of chiropractors | Probably acceptable, official register | No | To examine if chiropractors as opposed to medical practitioners have a real effect on health outcomes on a public health level, a more sophisticated type of analysis would be needed, taking into account a large number of variables that are linked to both the relative presence of chiropractors and the development of disease. This would have to be tested in multivariate models as it is not enough to investigate such variables one by one holding them up against the outcome variables (e.g. disease or mortality rates). |
Hart [20] (2007) Journal of Chiropractic Medicine Sherman College of Straight Chiropractic USA | Whole population? | Not reported | Chiropractic care not described Presence of chiropractors | Probably acceptable, official register | No | See above |
Hart [21] (2008) JVSR Sherman College of Straight Chiropractic USA | Whole population? | Not reported | Chiropractic care not described Presence of chiropractors | Probably acceptable, official register | No | See above |
Hart [22] JVSR (2008) JVSR Sherman College of Straight Chiropractic USA | Whole population? | Not reported | Chiropractic care not described Presence of chiropractors | Probably acceptable, official register | No | See above |
Hart [23] International Dose-Response Society (2013) Sherman College of Chiropractic USA | Whole population? | Not reported | Chiropractic care not described Presence of chiropractors | Not explained | No | See above |
First Author (Year) Journal Affiliation Country | Disorder studied | Type of treatment | Authors’/author’s conclusion in relation to effect/benefit of chiropractic treatment |
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Blum (2006) JVSR Private Practice USA | Early onset diabetes mellitus | -sacro-occipital technique -occipital fiber diagnosis and treatment -bloodless surgery -chiropractic Manipulative Reflex Technique -also: dietary modifications and exercise | “Within one month of treatment his glucose blood and urine levels had normalized and remained stable.” |
Fedorchuk (2011) AVSR Private Practice USA | Cholesterol levels | -diversified technique -active Release technique -chiropractic biomechanics of posture techniques (CBP) | “The clinical process documented in this report suggests that the combination of Diversified and CBP chiropractic care reduces subluxations and the tensegrity stress on the spinal column and nervous system. As a result of this reduced stress there is reduction of dysponesis which is evidenced by the improved quality of life and blood serum cholesterol levels.” |
Zielinski (2013) AVSR Life University College of Chiropractic, Emory University School of Public Health USA | Multiple conditions in a patient with dyslipidemia | -no life-style changes -torque release technique -diversified technique on C1 and sacrum/pelvis | “As care progressed, patient’s subjective stress levels decreased. […] We suspect his lipid levels were normalized as a consequence of decreased stress and subsequent normalizing in cortisol and inflammatory factors.” |
Slinger (2014) AVSR Private Practice USA | Cardiovascular disease risk factors | -diversified technique -lifestyle changes (diet and exercise) | “This retrospective case study reports on the effectiveness of chiropractic care in reducing vertebral and lower extremity subluxation findings as well as lowering the risk factors of cardiovascular disease” (serum cholesterol and lipid panels) |
Knowles (2015) AVSR Private Practice USA | Heart rate variability (as a proxy for a healthy state) | Network spinal analysis care | “After 6 months of Network care, follow-up examinations were performed: heart rate variability, […]. Surface EMG demonstrated an improvement in all areas of tension exhibited at the initial exam”
EMG = Electromyography
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First author, year of publication, name of journal, affiliation, country;
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Research question(s)/purpose of the study;
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Type of manipulative therapy/chiropractic treatment;
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Outcome variables for studied condition;
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Authors’/author’s conclusion in relation to effect/benefit of chiropractic treatment.
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Methodological considerations
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Design
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Comparison with non-treated (placebo) or an otherwise treated group;
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Random and concealed allocation to treatment groups;
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Main outcome variable(s) validated in some way;
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Assessor blinded to treatment group.
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Were differences between groups tested for statistical significance in relation to effect/benefit of treatment?
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Comments by reviewers in relation to major methodological improvements needed to test effect/benefit of intervention.
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First author, year of publication, name of journal, affiliation, country;
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Research question(s)/purpose of the study;
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Design;
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Study population;
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Outcome variables;
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Which factors associated with cause were included?
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Authors’/author’s conclusion in relation to effect/benefit of chiropractic treatment.
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Selection of study subjects (whole population, random selection, convenience sample);
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Response/Non response comparison;
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Definition of chiropractic treatment;
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Outcome variables validated in some way;
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Control for other variables that could have an effect on outcome;
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Comments by reviewers in relation to major methodological improvements needed to test effect/benefit of intervention.
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First author, year of publication, name of journal, affiliation, country;
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Disorder studied;
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Type of treatment;
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Authors’/Author’s conclusion in relation to effect/benefit of chiropractic treatment.
Data extraction and analysis
Results
Descriptive information
References | Hannon [8] | Hand search |
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Vora GS, Bates HA. The effect of Spinal Manipulation on the Immune System (A Preliminary Report). ACA Journal of Chiropractic. 1980;14:S103–105. | X | |
Masarsky CS, Weber M. Chiropractic and Lung Volumes – A retrospective Study. ACA Journal of Chiropractic. 1986;20(9):65–67. | X | |
Lott GS, Sauer AD, Wahl DR, Kessinger J. ECG Improvements Following the Treatment Combination of Chiropractic Adjustments, Diet, and Exercise Therapy. The Journal of Chiropractic Research and Clinical Investigation. 1990;6(2):37–39. | X | |
Hoiriis KT, Owens EF, Pfleger B. Changes in general health status during upper cervical chiropractic care: A practice-based research project. Chiropractic Research Journal. 1997;4(1):18–26. | X | |
Owens EF, Hoiriis KT, Burd D. Changes in General Health Status During Upper Cervical Chiropractic Care: PBR Progress Report. CRJ. 1998;5(1):9–16. | X | |
Kessinger R, Boneva D. Neurocognitive Function and the Upper Cervical Spine. CRJ. 1999;6(2):88–89. | X | |
Miller JA, Bulbulian R, Sherwood WH, Kovach M. The Effect of Spinal Manipulation and Soft Tissue Massage on Human Endurance and Cardiac and Pulmonary Physiology – A Pilot Study. The Journal of Sports Chiropractic & Rehabilitation. 2000;March:11–15 | X |
Articles | PubMed | Embase | ICL search 2 | JCM | JVSR | Hannon [8] | |
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Clinical studies | Kessinger [11] (1997) | X | X | ||||
Kessinger [12] (1998) | X | X | |||||
Morter [13] (1998) | X | X | |||||
Campbell [14] (2005) | X | X | |||||
Boone [15] (2006) | X | ||||||
McMaster [16] (2013) | X | X | |||||
Jones [17] (2014) | X | ||||||
Goertz [18] (2016) | X | ||||||
Population studies | Hart [19] (2007) | X | |||||
Hart [20] (2007) | X | X | |||||
Hart [21] (2008) | X | ||||||
Hart [22] (2008) | X | ||||||
Hart [23] (2013) | X | X | |||||
Case studies | Blum [24] (2006) | X | |||||
Fedorchuk [25] (2011) | X | ||||||
Zielinski [26] (2013) | X | ||||||
Slinger [27] (2014) | X | ||||||
Knowles [28] (2015) | X |
Reasons for inclusion in the review
For which physical, non-musculoskeletal diseases has the effect/benefit of chiropractic treatment been studied in the chiropractic literature?
Which study designs have been used and were they relevant to uncover effect or benefit of intervention?
Was the basic methodological quality sufficient to make results credible?
Clinical studies
Population studies
Case reports
What evidence of effect is there?
Discussion
Summary
General methodological considerations
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Individual cases, usually picked out on the basis of their uniqueness, do not reflect general patterns.
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Individual successful cases, even if correctly interpreted must be validated in a ‘proper’ research design, which usually means that presumed effect must be tested in a properly powered and designed randomized controlled trial.
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One or two successful cases may reflect a true but very unusual recovery, and such cases are more likely to be written up and published as clinicians do not take the time to marvel over and spend time on writing and publishing all the other unsuccessful treatment attempts.
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Recovery may be co-incidental, caused by some other aspect in the patient’s life or it may simply reflect the natural course of the disease, such as natural remission or the regression towards the mean, which in human physiology means that low values tend to increase and high values decrease over time.
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Cases are usually captured at the end because the results indicate success, meaning that the clinical file has to be reconstructed, because tests were used for clinical reasons and not for research reasons (i.e. recorded by the treating clinician during an ordinary clinical session) and therefore usually not objective and reproducible.
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The presumed results of the treatment of the disease is communicated from the patient to the treating clinician and not to a third, neutral person and obviously this link is not blinded, so the clinician is both biased in favour of his own treatment and aware of which treatment was given, and so is the patient, which may result in overly positive reporting. The patient wants to please the sympathetic clinician and the clinician is proud of his own work and overestimates the results.
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The long-term effects are usually not known.
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Further, and most importantly, there is no control group, so it is impossible to compare the results to an untreated or otherwise treated person or group of persons.
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The main problem was that five out of the eight prospective outcome studies did not have a control group. Clearly, in order to find out if a treatment has an effect, a comparison to no treatment must be made or a comparison to another treatment that is known to have an effect. Further, this ‘no treatment’ group must be masked into a sham treatment, to allow for the placebo effect that probably always plays a role in clinical practice.
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Interestingly, only two of the five prospective studies without a control group mentioned this as a problem. Nevertheless, instead of discussing this lack of control group, the authors of three articles mentioned that there would be a need for larger studies. However, larger studies will not remedy this fundamental flaw in the study design.
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When comparing outcomes between different types of treatment approach, the sham group is not relevant but the study subjects should not have a preference for one type of treatment or the other. Therefore, it is difficult to perform such studies on chiropractors, chiropractic patients and chiropractic students, as study participants should be ‘naïve’. To account for expectation bias, study subjects’ preferences should be elicited prior to the start of the study and taken into account during the analysis.
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When establishing effect or benefit of treatment, it is also necessary that the study subjects are captured at about the same period of time, as the disease, the treatment and study subjects may change over time. It is usually not a good idea to simply compare one type of treatment with the results of another type of treatment carried out x number of years ago or at the same time in some other clinic. The reasons why the study subjects should be captured in the same place is that they should be fairly representative of that patient group, and different countries, areas of a country, clinics and clinicians may attract fundamentally different types of patients with inherently different prognoses.
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The allocation into one study group or another should be done in a random fashion, in such a way that nobody can guide different patient types into a specific group because they seem more suitable in that group. Random allocation usually avoids clustering of certain patient types in one group, which may have an effect on treatment outcome if these groups react differently to treatment.
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Other important aspects are that the person who assesses the outcome should not be the person who treats the patient and should also be blind to which study group the person assessed belongs to. The outcome variables should be objective and relevant in relation to measuring whether the disease improved or not. Further, tests should be reliable when carried out by different examiners and also consistent (reproducible) within the study subject if the test is carried out over several times, to ensure that any changes occurring over time are due to the treatment and not to the instability of the test or inability of the tester.