Reporting of adverse effects in randomised clinical
trials of chiropractic manipulations: a systematic review
Edzard Ernst, Paul Posadzki
Objective To systematically review the
reporting of adverse effects in clinical trials of chiropractic manipulation.
Data sources Six databases were searched
from 2000 to July 2011. Randomised clinical trials (RCTs) were considered, if
they tested chiropractic manipulations against any control intervention in human
patients suffering from any type of clinical condition. The selection of
studies, data extraction, and validation were performed independently by two
Results Sixty RCTs had been published.
Twenty-nine RCTs did not mention adverse effects at all. Sixteen RCTs reported
that no adverse effects had occurred. Complete information on incidence,
severity, duration, frequency and method of reporting of adverse effects was
included in only one RCT. Conflicts of interests were not mentioned by the
majority of authors.
Conclusions Adverse effects are poorly
reported in recent RCTs of chiropractic manipulations.
Chiropractic has been defined the “diagnosis,
treatment and prevention of mechanical disorders of the musculoskeletal system
and the effects of these disorders on the function on the nervous system and
general health”.1 The hallmark
intervention of chiropractic is spinal manipulation which is used to adjust
spinal “subluxations”. The founder of chiropractic believed that 95%
of all diseases are caused by vertebral
Many authors have expressed doubts about the safety of
spinal manipulation. A particular concern relates to vascular accidents caused
by arterial dissection after upper spinal
manipulation.3,4 The main aim of this review is
to examine the reporting of adverse effects of chiropractic manipulations in
recent randomised clinical trials (RCTs).
Literature searches were performed in July 2011 to
identify adverse effects reported in randomised clinical trials (RCTs) of
chiropractic manipulation. The following databases were searched (from January
2000 to July 2011): Cochrane Library, MEDLINE, EMBASE, CINAHL, AMED,
PsycINFO. Chiropractic manipulation OR chiropractic OR spinal manipulation
were employed as Medical Subject Heading (MeSH) terms or key words for
The reference lists of all located articles were
scanned for further relevant literature. Additionally, relevant published book
chapters and our own extensive files were hand-searched for further articles. No
language barriers were imposed.
Exclusion criteria were trials by osteopaths,
physiotherapists and medical practitioners, or trials by chiropractors not
testing chiropractic manipulation. Data were extracted according to pre-defined
criteria (Table 1 and 2
) by both authors. Discrepant
opinions were settled through discussion.
Sixty RCTs met our eligibility
criteria.5–64 Twenty-nine RCTs (48%) did
not report information regarding
and 31 RCTs (52%) did. Of those 31 RCTs, 16 (51.6%) reported that no adverse
effect of chiropractic manipulations occurred during the
Eight of the 31 RCTs mentioning AEs described the method of establishing AEs:
questionnaire,23 questionnaire and telephone
notes.9 Eleven RCTs mentioned the severity of
AEs.7,8,17,19,27,29,31,33,34,46,51 Four RCTs
reported the duration of AEs.27,29,34,51 One
RCT reported the frequency of AEs.38 One RCT
(1.6%) reported complete information on AEs, i.e. method of reporting, severity,
duration and frequency.38
The source of funding was provided in 47 RCTs
and in 13 RCTs (21.6%) this information was missing
Conflicts of interest were declared in 17 RCTs
and in 43 RCTs (71.7%) this information was
Table 3 summarises the findings related to AEs as a function
of source of funding, conflict of interest and affiliation to chiropractic
institutions. Sizable proportions (55.8%) of RCTs without a declaration of
interest also failed to mention AEs. The method of reporting AEs was not
mentioned in large proportions of RCTs without a statement of conflict of
interest (86%) or with affiliations to chiropractic institutions (91.8%).
The severity of AEs was not reported in 83.7% of RCTs
without declarations of conflict of interest, and in 81% with affiliations to
chiropractic institutions. The duration of AEs was not reported in 95.3% of RCTs
without declarations of conflict of interest, and in 91.8% of RCTs with
affiliations to chiropractic institutions. The frequency of AEs was not reported
in 95.3% of RCTs without declarations of conflict of interest and in 100% with
affiliations to chiropractic institutions.
A remarkably low number of RCTs of chiropractic manipulation
was published during the last decade: 60 RCTs compared to nearly 300 000 RCTs
that emerged in the conventional healthcare during the same
period.65 The reasons for this paucity of RCTs
might be complex and could involve a shortage of funding and a general lack of
insight by chiropractors into the necessity of submitting their therapeutic
claims to scientific tests.66
Forty eight per cent of RCTs reviewed here fail to mention
AEs and sizable proportions of those which do mention AEs provide no information
as to how AEs were recorded, their severity, duration or frequency (Table 2).
For instance, of the 31 RCTs reporting AEs, only 8 (25.8%) mentioned the method
of reporting, 11 (35.4%) the severity, 4 (12.9%) the duration, one (3.2%) the
frequency of AEs. Further analyses (Table 3) seem to suggest that not declaring
conflicts of interest and being affiliated to chiropractic institutions might be
risk factors for incomplete reporting of AEs.
Guidelines of reporting or designing RCTs strongly emphasise
that details on AEs are an ethical imperative in clinical
research.e.g.67 Our review seems to indicate
that, in chiropractic research, this imperative is frequently ignored.
Similarly, the source of funding and any conflicts of interest should be
declared in publications of RCTs.67
Our review shows that, in chiropractic research, this is
frequently not the case. Our analyses also suggest that being affiliated to a
chiropractic institution, arguably a conflict of interest in
itself,68 is associated with poor reporting of
AEs. Twelve of the RCTs were funded by the US National Center for Complementary
Medicine,10,11,19,20-22,25,32-35 and 19 by
Of those funded by chiropractors, 6 (31%) failed to report
13,17,22,51,60 Forty-three (71.7%) RCTs failed
to report conflicts of interest. Similar deficits in ethical standards have also
been noted in other areas of alternative medicine
Several hundred severe complications after upper spinal
manipulations have been reported.e.g.70,71 The
estimates as to the incidence of these complications vary
hugely.72 The opinion of most chiropractors
that such complications are extreme rarities is partly based on the fact that
clinical trials of chiropractic manipulation fail to demonstrate the existence
of such events. Our review shows that authors of such RCTs frequently neglect to
mention AEs. Thus the lack of trial evidence for severe complications could well
be due to the failure of triallists to report AEs.
Our review also points to an overt contradiction regarding
the incidence of mild to moderate AEs. Sixteen of the 31 RCTs mentioning AEs
stated that no AEs occurred and the RCTs which did report AEs provided incidence
figures between 1.4%21and 50%
61 Numerous prospective studies specifically
designed to investigate AEs of chiropractic manipulation agree that about 50% of
patients experience mild to moderate AEs after such
treatments.72 Method of monitoring AEs in RCTs
strongly influences their incidence.73,74 Thus
lack of rigorous methods for assessing AEs might have generated spuriously low
incidence figures in RCTs.
In conclusion, this review shows that AEs are poorly
reported or not mentioned at all in RCTs of chiropractic manipulations. Further
concerns relate to the prevalent failure to report conflicts of interest or
sources of funding.
Competing interests: None
Source of funding: PP has a Fellowship
from Pilkington Family Trust.
Author information: Paul Posadzki, Honorary
University Fellow; Edzard Ernst, Director; Complementary Medicine, Peninsula
Medical School, Universities of Exeter & Plymouth, Exeter, UK
Complementary Medicine, Peninsula Medical School, Universities of Exeter &
Plymouth, Veysey Building, Salmon Pool Line,
Exeter, EX2 4SG, UK. Email:
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