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ORIGINAL RESEARCH
The Danish Chiropractic Low Back Pain Cohort
(ChiCo): Description and Summary of an Available
Data Source for Research Collaborations
This article was published in the following Dove Press journal:
Clinical Epidemiology
Alice Kongsted
1,2
Orla Lund Nielsen
1
Henrik Wulff Christensen
1
Jan Hartvigsen
1,2
Klaus Doktor
1,2
Peter Kent
2,3
Tue Secher Jensen
1,2,4
1
The Nordic Institute of Chiropractic and
Clinical Biomechanics, Odense M 5230,
Denmark;
2
Department of Sports Science
and Clinical Biomechanics, University of
Southern Denmark, Odense, Denmark;
3
School of Physiotherapy and Exercise
Science, Curtin University, Perth,
Australia;
4
Diagnostic Centre, Silkeborg
Regional Hospital, Silkeborg, Denmark
Background: Back pain is among the most frequent reasons for care seeking globally.
Observational clinical cohorts are useful for understanding why people seek care, the content
of that care, and factors related to prognosis. This paper describes the Danish Chiropractic
low back pain Cohort (ChiCo) and summarizes the primary characteristics of the population
to inform the scientic community of the availability of these data as a resource for
collaborative research projects.
Methods: Adults seeking chiropractic care for a new episode of non-specic back pain were
enrolled at the initial visit and followed up after 2, 13, and 52 weeks, with a subpopulation
having weekly follow-ups for 1 year. Patient-reported and clinical-reported data were
collected in an electronic database using the REDCap software (REDCap Consortium,
projectredcap.org). Variables were chosen to measure pre-dened research domains and
questions and to capture information across health constructs deemed relevant for additional
research. Non-responders at 13 and 52 weeks were contacted by phone to maximize follow-
up data and explore differences on core outcomes between responders and non-responders.
Results: A total of 2848 patients (mean age 45 years, 59% men) were included from 10 clinics
with 71%, 68% and 64% responding to follow-ups at 2, 13 and 52 weeks, respectively. Most
participants (82%) were employed, nearly half reported current LBP for 1–7 days, and 83% had
experienced LBP episodes previously. We did not identify indications of serious attrition bias.
Conclusion: We have described the aims and procedures for establishing the ChiCo cohort,
characteristics of the cohort, and available information about attrition bias. These data have
the potential to be linked, at an individual participant level, to the extensive Danish popula-
tion-based registries that measure diverse health and social characteristics.
Keywords: chiropractic, cohort studies, low back pain, primary care
Background
Low back pain (LBP) affects people of all ages. It is burdensome for individuals
and societies and is now the leading cause in the world of years lived with disability
for both males and females.
1,2
For example, half of adults in Denmark report back
pain within the previous 2 weeks, 20% of all sick days in Denmark (5.8 million
people) are due to LBP, and the annual cost of LBP in Denmark alone is at least
900 million Euro.
3
Collectively, guidelines from around the globe endorse the use of non-
pharmacological and non-surgical interventions such as advice to remain active
and at work, exercise, and manual therapy as front line care for people with LBP.
4
Correspondence: Alice Kongsted
Email akongsted@health.sdu.dk
Clinical Epidemiology Dovepress
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However, more knowledge about who seeks care for their
LBP, what happens during the clinical consultation, what
treatments are given, how the presence of other co-
occurring health conditions inuence prognosis, and how
expectations and preconceived ideas about LBP affect
prognosis and the clinical course is needed before these
recommendations can be effectively implemented. Also,
an apparent mismatch between clinical guidelines dis-
couraging routine imaging for LBP and the use of imaging
asks for knowledge about decisions and consequences
related to diagnostic imaging. Large observational studies
based on data collected at the point of care are well suited
to answer these important clinical questions and have
therefore been recommended to study spine pain
conditions.
5
In Denmark chiropractors are primary contact health-
care providers within the universal healthcare system and
most people who seek chiropractic care do so because of
LBP.
6
Previous research indicates that as many as 30% of
people seeking care for LBP choose to see a chiropractor
as their rst contact to the health-care system.
7
Danish
chiropractic practice therefore provides a good setting for
studying LBP in primary care, and Danish chiropractors
and their patients have been willing to participate in
research. For example, a previous cohort study of people
seeking care for LBP from Danish chiropractors provided
important knowledge about the clinical course of LBP in
chiropractic care,
8
as well as determined to what extent
this course can be best predicted by chiropractors by
standardised screening tools or by patient expectations of
recovery.
9–11
Furthermore, results from that cohort identi-
ed ways for chiropractors to easily screen for psycholo-
gical factors inuential on the prognosis of patients with
LBP,
12
explored which factors were important for patients
that consider themselves to be recovered,
13
and also
helped identify which parts of the clinical examination
best predicted outcomes of treatment.
14,15
Many new research questions have emerged since the
collection of that rst cohort in 2010 −2012, and we there-
fore designed a new and larger cohort sample of people
seeking care for LBP from Danish chiropractors. The aim
of this paper is to present that new cohort - the Danish
Chiropractic low back pain Cohort (ChiCo) – and describe
the data collection procedures, summarize baseline char-
acteristics of that sample, and inform the scientic com-
munity of the availability of these data as a resource for
collaborative research projects.
Methods
Design and Feasibility
ChiCo is a longitudinal observational cohort consisting of
adults seeking care for LBP at 10 chiropractic clinics in
Denmark. Patient enrolment occurred between
1 November 2016 and 21 December 2018. Baseline data
include information from patient-reported information col-
lected prior to seeing the chiropractor (Baseline 1), clinical
data entered by the clinician during or shortly after the
baseline examination (Clinician Questionnaire), and
further patient-reported data after the rst consultation
with the chiropractor (Baseline 2). Follow-up data were
collected two weeks after inclusion (Follow-up 2 weeks),
and 3 and 12 months after inclusion (Follow-up 3 months
and Follow-up 12 months). A subpopulation received and
answered SMS (text) messages weekly for the duration of
one year starting on the seventh day after inclusion.
A feasibility test of study logistics, including clinician
and patient inclusion, attrition rates, electronic question-
naire procedures, and weekly SMS tracking, was con-
ducted and evaluated in four chiropractic clinics prior to
the start of the main study.
Three studies were published based on parts of the
cohort before data collection was nished.
16,17
Setting
Chiropractic clinics were a convenience sample invited from
the Central Administrative Region of Denmark that covers
approximately 1.3 million inhabitants (2018). Clinics were
identied from personal knowledge about clinics in the area.
It was a requirement for participation that the clinics had
digital x-ray systems using the national KirPACS (picture
archiving and communication system), because that would
serve as a single point of access to all images. Only medium
or large size clinics were invited to ensure adequate recruit-
ment of study participants within a reasonable timeframe.
Chiropractors in Denmark are self-employed, and almost
all clinics (94%) operate under the agreement between the
Danish Chiropractor’s Association and the Danish Regions
where for most services around 20% is paid by the region and
80% by the patient directly or by a private insurance.
Reimbursement for chiropractic services is independent of
referral from GPs, so many patients self-refer.
Approximately 25% of chiropractic clinics have at least one
physiotherapist as part of the clinical staff and 60% have
exercise facilities;
18
for clinics recruiting for ChiCo this was
90% and 60%, respectively.
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Introductory meetings with clinicians and secretaries
conveying information about the study’s aims, research
areas and logistics were held at the rst four clinics prior
to commencement of patient inclusion in November 2016.
Two clinics were added in May 2017, another two in
November 2017, and in March 2018 the last two were
included. In addition, written instructions and checklists
for procedures and data collection were provided for clin-
icians and secretaries.
Once a week during the baseline inclusion period the
clinics were contacted by a research assistant who would
answer questions from the clinics on project-related pro-
cedures and clarify issues, such as why clinician question-
naires had not been completed or why duplicate patients
were present in the project database. During the patient
inclusion phase clinics were contacted monthly to give
feedback on the number of included patients and to
thank the clinics for participating in the project. Clinics
were reimbursed with DKK 225 (€ 30) for each patient
included, in order to compensate for the altered workow
and time taken for completion of the clinician-reported
questionnaires.
Participants
People were eligible for participation if they consulted the
involved chiropractic clinics with a new episode of LBP
with or without leg pain, were aged 18 years or older and
able to complete electronic questionnaires in Danish.
A new episode was dened as contacting the clinic for
a new or recurring LBP problem for which they were not
in an ongoing course of treatment or long-term manage-
ment. People with suspected systemic pathology leading to
referral for diagnostic workup and people referred for
acute surgical assessment were not eligible.
Assuming 15% of patients in Danish chiropractic care
receive imaging, 5000 participants were the estimated
sample size needed as approximately 750 participants
with radiographs, MRI- or CT-scans were needed for sub-
projects about imaging that had the highest demands for
numbers included.
19
Follow-up by SMS questions was
planned only for the rst 1200 participants to reduce
burden on participants and costs.
Data Collection Setup
Questionnaire data were collected and stored using the
online system REDCap (Research Electronic Data
Capture) hosted and supported by the Odense Patient
data Explorative Network (OPEN). The use of application
programming interface (API) connections from REDCap
allowed record ID and mobile phone number to be
exported to an SMS-Track service that automated weekly
distribution of text message questions.
Eligible patients received an iPad upon arrival to the
clinic congured such that only direct access to data entry
in REDCap was possible. Activation of the software applica-
tion resulted in REDCap creating a new automatically num-
bered record. The rst screen informed the patient about the
project and requested his or her consent to participate and
included details about how contact information and sensitive
personal data would be managed within the project. Only by
providing consent was it possible for the invited patients to
enter their name and the individual unique Danish Central
Person Registry (CPR) identication number and thereby get
access to the Baseline 1 questionnaire. This procedure also
ensured that no follow-up questionnaires would be sent
unless consent had been given.
Using contact information from Baseline 1, the
Baseline 2 questionnaire was sent to the participant’s
email after a delay of 15 minutes, which allowed them to
respond to it after the consultation with the chiropractor in
the clinic or from home using smartphone, tablet or PC.
Non-responders to Baseline 2 received an electronic
reminder after two days. Upon completion of Baseline 1,
follow-up questionnaires were automatically scheduled
after 14, 91 and 365 days. In case of non-response, an
electronic reminder was sent after three days for follow-up
2 weeks, and seven days after for follow-up 3 months and
follow-up 12 months. Participants who did not respond to
the email reminder were contacted by telephone by
a research assistant who checked for valid email address,
reinforced the importance of high response rates, and
asked for permission to resend the questionnaire.
From 30 November 2017 onwards, these phone contacts
also included the asking of questions on a few core outcomes
(see section Follow-up interviews below). Replies were
registered separately by the research assistant and the parti-
cipant was still asked to complete the full questionnaire.
Text messages for the SMS-Track subpopulation were
sent weekly for 52 weeks in the late afternoon on the same
weekday as the inclusion. Participants were contacted by
phone if they had not responded to two or more subse-
quent messages.
Baseline Questionnaires
Questionnaires were selected to cover the constructs rele-
vant to predened research areas and match those in
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previous studies. Validated questionnaires were used
where possible, within the constraints of needing to limit
the total number of questions.
Patient-Reported Questionnaires
The Baseline 1 questionnaire included items that were
likely to be inuenced by the initial consultation with the
chiropractor. The Baseline 2 questionnaire contained
demographic and background information deemed less
likely to be clinician inuenced, and questions about the
patient’s experience of the rst consultation. The following
is a summary of the constructs covered in the question-
naires by domain (for greater detail see Supplementary
File 1 (ChiCo Codebook Patient)).
Patient Demographics and Social Factors
Information on participants included demographics, gen-
eral health, education, family factors and work situation.
Pain and LBP History
Information on LBP history included treatment for current or
previous low back pain episodes, triggers of onset of LBP,
previous imaging, and pain trajectory pattern over the pre-
vious 12 months. Pain intensity was rated on numeric rating
scales (NRS) for back pain and leg pain separately,
20
and
participants were asked about duration of current episode and
number of days with LBP within the past year.
Expectations and Reassurance
Participants indicated their expectations relating to the consul-
tation by items on expectations for examination, treatment,
advice and information about the condition, prognosis and
expected course. Recovery expectations were measured by
an item on the Örebro Musculoskeletal Pain Screening
Questionnaire (OMPQ).
21
Perceived reassurance was mea-
sured by the Consultation-based Reassurance Questionnaire
(CRQ).
22,23
Psychological Domain
Information collected about psychological factors included
the ability to control pain, and feeling depressed or
stressed as assessed by the OMPQ.
21
Fear avoidance of
work activities was measured by the Fear-Avoidance
Beliefs Questionnaire, work subscale (FABQ-W),
24,25
and fear of movement by two items from the Tampa
Scale for Kinesiophobia (TSK).
26
Illness Perception
Perception and beliefs about LBP were assessed by asking
about the perceived cause of LBP (cause component of the
Illness Perception Questionnaire (IPQ)),
27
attitudes
towards imaging,
28
and back beliefs (Back Beliefs
Questionnaire (BBQ)).
29
Physical Function
Physical function was measured by assessing activity lim-
itation (Roland Morris 23-item Disability Questionnaire
(RMDQ)),
20,30
and self-perceived physical tness.
31
Risk Stratication Index
General risk of persistent disability was assessed by the
STarT Back Screening Tool.
32
Clinician Reported Data
The clinical examination data included: 1) inspection (eg,
Schober’s test and posture), 2) global range of motion and
segmental palpation for pain and stiffness,
33
3) neurologi-
cal examination of the lower extremity (straight leg raise,
tendon reexes, muscle strength, sensation),
34,35
4) ortho-
paedic examination (eg, SI joint pain provocation tests),
36
and 5) other examinations (eg, percussion, step-off
between spinous processes) (See Supplementary File 2,
ChiCo Codebook Clinicians). Additional clinician reported
information included: Presence of leg pain or symptoms,
suspected neurogenic pain, suspected inammatory back
disease or severe pathology, diagnosis resulting from the
examination, previous and planned diagnostic imaging
(radiograph, MRI or CT), indications for diagnostic ima-
ging, and treatment plan (Supplementary File 2, ChiCo
Codebook Clinicians).
Follow-Up Questionnaires
All follow-up questionnaires repeated the questions on low
back and leg pain intensity, ability to control pain, feeling
depressed or stressed, sick leave, current use of medication
and activity limitation. Additionally, the follow-up at 2
weeks asked about satisfaction with treatment and global
perceived effect (GPE). Both follow-ups at 2 weeks and 3
months repeated the STarT Back Screening Tool.
37
The
BBQ and information on other treatments were included in
follow-up 3 months and follow-up 12 months. In only the
follow-up 12 months questionnaire these additional items
were assessed: perceived cause of LBP, attitudes towards
imaging, imaging within the past year, pain trajectory
pattern over the past year, work ability and self-
perceived physical tness.
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Follow-Up Interviews
Participants who had not responded to the 3-month or 12-
month follow-ups were asked over the phone about their
response to the survey questions about typical LBP and leg
pain intensity within the past week, ability to control pain,
current use of medication, days off sick due to back pain
within the past 3 months and current sick leave, and
treatment by other practitioners.
Text Message Questions
The weekly SMS data collection consisted of three ques-
tions: (1) “How many days have you had back pain (or
back-related leg pain) within the last 7 days? (please
answer with one number from 0 to 7)”; (2) “How severe
was the pain typically on a scale from 0 to 10?”; and (3)
“How many days were you home last week from work or
study because of your back pain? (please answer with one
number from 0 to 7)”.
8
If the rst question was answered
with a “0”, no further questions were sent. During the rst
six weeks of the data collection, the third question (asking
about days home from work or study) was only sent
every second week and asked about the previous two
weeks.
Data Preparation
Biological sex, birthdate and age at inclusion were deter-
mined from the participants’ CPR number and date of
inclusion. The response status of questionnaires and date
of response relative to inclusion were created from
REDCap’s timestamps and logging information.
Inconsistencies in integer data (values out of the possible
range) were recoded as missing. Questions that remained
hidden unless triggered by afrmative response to an
introductory question were recoded as “0/No” or “.a”
(missing) as appropriate. For example, “No” to any pre-
vious treatment meant that previous treatment by all listed
health-care providers was also coded as “No”.
Imputation and Sum Scores
Sum scores were calculated from validated questionnaires
(RMDQ, BBQ, STarT, CRQ and FABQ) according to their
scoring algorithms (Supplementary le 1). To obtain sum
scores from incomplete questionnaires (with at least one
question answered), missing items on these scales were
imputed using chained multiple imputation informed by
scores on those ve questionnaires plus back pain intensity
at baseline, episode duration, age, sex and previous
treatment for back pain by a chiropractor. Due to very
unequal response distribution on ve RMDQ items these
were imputed using monotone sequential imputation.
Imputed values were restricted to the range of the original
response options. To simplify the use of data, we only
generated one imputed data set for the standard ChiCo
dataset, although one benet of multiple imputations is
analyses performed across multiple datasets. This was
judged to not introduce any considerable bias because
a maximum of 5% of responses were imputed for any of
the questionnaires.
Follow-Up Interviews
Missing items on 3- and 12-months follow-up question-
naires, which were obtained by phone interviews with
non-responders, were replaced by the responses obtained
at the interviews.
SMS-Track Clearing
SMS answers where the participant provided a non-
numerical response, eg, “two days” instead of 2, were
recoded to a single number whenever the equivalent was
obvious. Intervals (3–5), multiple numbers (3, 4, 6) or
decimals (3.5) were recoded to the average and rounded
(4). Numbers exceeding the logical range, single letters
and otherwise unintelligible messages were recoded as
missing.
Because the third SMS-question (days home from
work or study only) was sent only every second week
during the rst six weeks of the data collection and related
to the previous two-week period, the reported number of
days were distributed equally over the two relevant weeks.
For example, an answer of 6 in week 4 about days off
work during the past 14 days was recoded as 3 in week 3
and 3 in week 4.
Results
Feasibility Test
The feasibility testing was conducted with four clinics
enrolling a total of 55 patients, who all completed the
Baseline 1 questionnaire. Of these, 70% completed the
Baseline 2 questionnaire, 68% completed the 2 weeks
questionnaire, and 83% responded to the SMS-Track.
Based on interviews with secretaries, clinicians and
patients, only minor aspects of the procedures and ques-
tionnaires were changed, and data from the feasibility
testing was kept as part of the cohort.
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Inclusion and Response Rates
Ten clinics were recruited. We stopped inclusion of patient
participants at the end of 2018 with n=2848 participants
included (range 19–906 per clinic). That occurred because
the actual imaging rate (imaging performed before seeing
the chiropractor or at inclusion) was 37%, rather than the
expected 15%. During the inclusion period a total of 3165
record IDs were created. Removing of IDs erroneously
created by technical problems and exclusion of people
not fullling inclusion criteria resulted in a cohort of
2848 who completed the Baseline 1 questionnaire
(Figure 1). The lowest response rate was at the 12 months
follow-up with 64% responding to the questionnaire or
telephone interview (Figure 1). Of the non-responders,
381 (13%) did not answer any of the follow-up question-
naires or telephone questions. In addition, some question-
naire responses had single items missing because
answering all items was not compulsory.
A total of 1378 participants were included in the SMS
sub-cohort of whom 1000 (73%) responded to at least half
of the SMS questions, 928 (67%) responded to at least 42
of the 52 weekly SMS-questions, and 195 (14%)
responded for only two weeks or less.
Response times varied somewhat for the follow-up
points. On average, participants responded to the
Baseline 2 and the 2-week follow-up within 2 to 3 days,
and the 3 months follow-up within 7 to 11 days, with some
responding very late at all follow-up time points (Table 1).
Participant Characteristics
The cohort of ChiCo participants had a median age of
45years, approximately half had higher education, 82%
were employed and a minority reported any sick leave.
The current LBP episode duration was short (≤1 week) in
almost half of participants, but 83% had experienced LBP
before (Table 2).
Follow-Up Attrition Bias
We performed three types of drop-out analyses in order to
assess attrition bias: 1) comparing patient characteristics at
Baseline 1 between responders and non-responders of
Baseline 2 and follow-up at 2 weeks (Table 3); 2) compar-
ing patient characteristics at Baseline 1 between respon-
ders, interviewed participants and non-responders to the 3
month and 12 month follow-ups (Table 4); and 3) compar-
ing available outcomes at follow-ups between responders,
interviewed participants and non-responders to the 3 and
12 month follow-ups (Table 5).
Non-responders were younger than responders and
more often males, but these groups were successfully
reached by phone interviews (Table 4). No other substan-
tial differences on baseline characteristics were observed
between responders and non-responders (Tables 3 and 4).
Further, the interviews demonstrated that the mean
improvement experienced by non-responders to question-
naires was similar to the improvement in pain experienced
by the responders.
Discussion
To our knowledge, the ChiCo LBP cohort is the largest
and most comprehensive cohort of patients with LBP
seeking care from chiropractors, and also one of the largest
and most comprehensive cohorts of primary care patients
with LBP more generally. The participation rates at both
short- and long-term follow-up were satisfactory, and our
drop-out analyses indicate minimal attrition bias over the
one year. A subset of the cohort (N 1378) provided
answers to weekly SMS questions with 73% responding
to at least half of the 52 SMS questions. Some participants
responded late to follow-up questionnaires. That is not
unique to this sample, but available data on the time of
responding will allow researchers to determine how this is
handled in the specic future research projects using
ChiCo cohort data.
The ChiCo cohort was designed to answer research
questions within a number of pre-dened domains. These
include questions related to proling of Danish chiroprac-
tic patients; beliefs and attitudes of patients and clinicians
in relation to LBP and recovery from LBP and the impor-
tance of imaging for LBP; the value of imaging in people
seeking care from chiropractors for LBP; prevalence, risk
and prediction of sick leave among Danish chiropractic
patients; implementation of evidence/evidence-based prac-
tice among Danish chiropractors; validation of previously
identied LBP trajectories and prediction models in pri-
mary care patients with LBP; and a validation of the
Consultation Reassurance Questionnaire. That validation
study has been published on a subset of the cohort.
23
Follow-up times and variables were carefully chosen in
order to ensure that research questions within these pre-
specied areas of interest could be answered while keep-
ing the burden on participants and clinicians as low as
possible.
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Information collected on participants in ChiCo can be
merged with information from Danish national registries
in order to study outcomes related to broader questions.
For example, long-term healthcare consumption in pri-
mary care and in hospitals via the Danish National
Health Service register and the Danish National Patient
Register,
38,39
medication prescription from The Danish
National Prescription Registry, as well as social outcomes
like sick-leave and early retirement via the National
Registry on Social transfer Payments (the DREAM
Originally appointed ID’s: 1 Nov 2016 – 21 Dec 2018
•3165 Total
Not included in the project: 317
•66 Technical failure
•173 Declined consent
•74 Excluded, non-musculoskeletal cause of pain
•4 Excluded, age under 18 years
ChiCo Cohort / Baseline 1: 2848 (100%)
•2737 (96%) Completed questionnaire
•111 (4%) Partly responded questionnaire
Baseline 2: 2083 (73%)
•2029 (71%) Completed questionnaire
•54 (2%) Partly responded questionnaire
•765 (27%) Missing questionnaire
2-weeks follow-up: 2023 (71%)
•1989 (70%) Completed questionnaire
•34 (1%) Partly responded questionnaire
•825 (29%) Missing questionnaire
3-months follow-up: 1926 (68%)
•1705 (60%) Completed questionnaire
•20 (1%) Partly responded questionnaire
•201 (7%) Interview only
•922 (32%) Missing questionnaire
12-months follow-up: 1815 (64%)
•1459 (51%) Completed questionnaire
•27 (1%) Partly responded questionnaire
•329 (12%) Interview only
•1033 (36%) Missing questionnaire
Figure 1 Flowchart.
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Table 1 Response Times for Completed Questionnaires
Response Times Baseline 2
(N=2029)
2 Weeks
(N=1989)
3 Months
(N=1705)
12 Months
(N=1459)
Mean (SD); days after distribution 2.3 (3.8) 2.9 (5.3) 7.2 (10.6) 10.8 (20.5)
Median (IQR); days after distribution 1 (0–3) 1 (0–4) 3 (0–8) 4 (0–9)
Late response; n (%)* 105 (5.2%) 219 (11.0%) 78 (4.6%) 138 (9.5%)
Notes: *>7 days after distribution for baseline and 2 weeks follow-up; >1 month after distribution for 3 and 12 months follow-ups.
Table 2 Participant Characteristics
Participant Characteristics Baseline 2 Weeks 3 Months 12 Months
Age; mean (SD, full range) 44.6 (13.7; 18–87)
Sex, female; n (%) 1167 (41.0%)
BMI; mean (SD) 26.9 (5.0)
Smoker, yes; n (%) 336 (16.2%)
Longest education:
Higher or further education; n (%) 1040 (51.5%)
Vocational education; n (%) 594 (29.4%)
No qualifying education; n (%) 313 (15.5%)
Other education; n (%) 74 (3.7%)
Employment, yes; n (%) 2287 (82.2%)
Previous treatment for low back pain, yes; n (%) 1357 (66.4%)
Previous episodes with low back pain, yes; n (%) 1652 (83.3%)
Days with low back pain within past year, >30 days; n (%) 752 (37.5%)
Episode duration:
1–7 days; n (%) 1328 (47.0%)
1 week - 3 months; n (%) 1006 (35.6%)
>3 months; n (%) 494 (17.5%)
STarT Back Tool risk groups
Low; n (%) 1211 (42.5%)
Medium; n (%) 1014 (35.6%)
High; n (%) 623 (21.9%)
Current use of over the counter and/or prescribed pain killers for back pain, yes;
n (%)
1041 (51.0%)
Fear-Avoidance, FABQ Work subscale (0–42); mean (SD) 12.6 (9.4)
Days off sick within past 3 months; median (IQR) 0 (0–1)
Present sick leave, yes; n (%) 74 (4.8%) 43 (2.3%) 25 (1.3%) 20 (1.1%)
Back pain intensity, NRS (0–10); mean (SD) 6.7 (2.1) 3.7 (2.3) 2.3 (2.3) 2.3 (2.4)
Leg pain intensity, NRS (0–10); mean (SD) 3.0 (2.9) 1.9 (2.4) 1.3 (2.1) 1.1 (2.0)
Back Beliefs, BBQ (9–45); mean (SD) 32.2 (5.9) 32.8 (6.2) 32.0 (6.0)
Activity limitation, RMDQ (0–100); mean (SD) 55.0 (23.8) 30.3 (26.1) 19.7 (23.5) 20.0 (22.8)
Clinician reported working diagnosis
Non-specic LBP; n (%) 2372 (84.7%)
Back related leg pain WITHOUT nerve root involvement; n (%) 665 (23.8%)
Back related leg pain WITH nerve root involvement; n (%) 164 (5.9%)
Fracture; n (%) 14 (0.5%)
Initial suspicion of systemic pathology (Cancer, Cauda equina syndrome,
Inammatory rheumatoid arthritis, Infection)*; n (%)
31 (1.1%)
Note: *Participants not excluded because pathology not conrmed.
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registry).
40
Merging of data from these and other national
registries can be performed via Statistics Denmark for
a minimal fee that covers their expenses for the handling
of data.
A cohort study is designed to study the development
and determinants of health and disease in a group of
individuals who share a common experience or condition,
and across subgroups within the cohort.
41
Ideally, prog-
nostic studies should begin at zero time, ie, at a well-
dened time point that is common for all participants in
the cohort, such as onset of disease (inception cohort),
time of diagnosis, or beginning of treatment.
42
Here we
include participants at the beginning of treatment for
a new episode of LBP for which there was no ongoing
treatment or long-term management. This denition of
zero time has inherent problems in LBP because for
many people it is a chronic recurrent condition and pre-
vious care is very common.
43,44
In addition, people with
higher levels of chronicity and disability, ie, chronic expo-
sure, are more likely to seek care, which may result in an
over-representation in a cohort where care seeking is the
event that triggers inclusion.
41,45
We collected an exten-
sive set of variables at baseline in order to be able to
describe this cohort thoroughly, to study the inuence of
these variables on prognosis, and to adjust for factors that
may confound relationships between baseline characteris-
tics (exposures) and outcomes for the investigation of
causal questions. To reduce the risk of prevalence-
incidence bias, it will be possible to use information
about participants’ LBP history to dene homogenous
subsets within the cohort for specic research questions.
Danish chiropractic patients with LBP are not repre-
sentative of Danish primary care patients with LBP. They
have been shown to be younger, better educated, more
often males, and have a better general health with fewer
comorbidities when compared to people who seek care for
LBP from Danish GPs.
46
Also, patient proles in the
cohort cannot be assumed to be generalizable to chiroprac-
tic care globally. For example, a scoping review of people
seeking chiropractic care for all reasons found a larger
proportion of female patients (57%) than in the ChiCo
cohort (41%).
47
Whether this is due to differences across
conditions (LBP versus all) or countries, or related to
different attrition bias are unknown. Still, there is no
reason to believe that relationships between patient factors
investigated in the ChiCo cohort would generally not
apply to other circumstances. This is to be considered for
each question investigated. It is theoretically possible that
only recruiting from larger clinics may have introduced
some bias into the sample and patients in large clinics may
more often be offered cross-disciplinary treatment, as the
enrolled clinics more often had physiotherapist as part of
the team as compared to Danish chiropractic clinics in
general. We do not believe that recruiting in only one
region of Denmark is likely to have biased the sample
because chiropractic in Denmark is a very homogenous
profession that is regulated and well integrated into the
national healthcare system. Similarly, participant baseline
demographics in the ChiCo cohort are comparable to those
of the previous but smaller Danish cohort of chiropractic
patients with LBP (n = 934) that was based on a national
sample.
46
The only exceptions were a slightly lower pro-
portion of females in the ChiCo cohort (41% versus 45%)
and a higher proportion of participants without
a qualifying education (16% versus 7%).
In 2018, a group of international leading experts pub-
lished a Call to Action in The Lancet that outlined
a number of research priorities in order to address
Table 3 Characteristics at Baseline 1 of Responders and Non-Responders to Baseline 2 and 2-Weeks Follow-Up
Patient Characteristics at Baseline* Baseline 2 2 Weeks
Responders
(N=2083)
Non-Responders
(N=765)
Responders
(N=2023)
Non-Responders
(N=825)
Age; mean (SD) 46.1 (13.5) (n=2083) 40.5 (13.4) (n=765) 46.6 (13.4) (n=2023) 39.6 (13.1) (n=825)
Sex, female; n (%) 918 (44.1%) (n=2083) 249 (32.6%) (n=765) 872 (43.1%) (n=2023) 295 (35.8%) (n=825)
Episode duration, >7 days; n (%) 1109 (53.6%) (n=2070) 391 (51.6%) (n=758) 1078 (53.6%) (n=2011) 422 (51.7%) (n=817)
Back pain intensity, NRS (0–10); mean (SD) 6.7 (2.0) (n=2042) 6.6 (2.2) (n=749) 6.7 (2.0) (n=1987) 6.7 (2.1) (n=804)
Leg pain intensity, NRS (0–10); mean (SD) 3.0 (2.9) (n=2039) 2.7 (2.8) (n=744) 3.0 (2.9) (n=1980) 2.9 (2.9) (n=803)
FABQ work subscale (0–42) 12.2 (9.2) (n=1715) 13.7 (10.0) (n=636) 12.2 (9.1) (n=1650) 13.7 (10.1) (n=701)
Activity limitation, RMDQ (0–100) 55.4 (23.6) (n=2083) 53.6 (24.5) (n=765) 55.0 (23.5) (n=2023) 54.8 (24.8) (n=825)
Use of medication, yes; n (%) 1041 (51.0%) (n=2043) N/A 924 (51.4%) (n=1797) 117 (47.6%) (n=246)
Note: *All except medication are from Baseline 1.
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Table 5 Outcomes at Follow-Ups for Responders, Interviewed Participants and Non-Responders at 3- and 12-Month Follow-Ups
Patient Characteristics 3 Months 12 Months
Responders to Questionnaires
(N=1725)
Interviewed
(N=201)
Non-Responders
(N=922)
Responders to Questionnaires
(N=1486)
Interviewed
(N=329)
Non-Responders
(N=1033)
Back pain intensity at 2 weeks FU, NRS (0-10);
mean (SD)
3.7 (2.3)
(n=1603)
3.6 (2.3)
(n=85)
3.8 (2.3)
(n=325)
3.7 (2.3)
(n=1403)
3.9 (2.4)
(n=188)
3.8 (2.3)
(n=422)
Leg pain intensity at 2 weeks FU, NRS (0-10); mean
(SD)
1.9 (2.4)
(n=1596)
1.7 (2.1)
(n=84)
2.0 (2.5)
(n=325)
1.8 (2.3)
(n=1395)
2.2 (2.6)
(n=187)
2.0 (2.5)
(n=423)
Back pain intensity at 3 months FU, NRS (0-10);
mean (SD)
2.3 (2.3)
(n=1718)
2.1 (2.5)
(n=200)
N/A 2.3 (2.2)
(n=1378)
2.3 (2.5)
(n=211)
2.6 (2.4)
(n=329)
Leg pain intensity at 3 months FU, NRS (0-10);
mean (SD)
1.3 (2.1)
(n=1717)
1.0 (2.1)
(n=201)
N/A 1.3 (2.0)
(n=1378)
1.2 (2.2)
(n=210)
1.5 (2.2)
(n=330)
Back pain intensity at 12 months FU, NRS (0-10);
mean (SD)
2.3 (2.4)
(n=1463)
2.0 (2.3)
(n=127)
2.4 (2.5)
(n=221)
2.3 (2.4)
(n=1482)
2.1 (2.6)
(n=329)
N/A
Leg pain intensity at 12 months FU, NRS (0-10);
mean (SD)
1.1 (2.0)
(n=1461)
0.8 (1.9)
(n=127)
1.2 (2.1)
(n=221)
1.2 (1.9)
(n=1480)
0.9 (2.2)
(n=329)
N/A
Table 4 Baseline Characteristics of Responders to Questionnaires, Participants Interviewed and Non-Responders at 3- and 12-Month Follow-Ups
Patient Characteristics at
Baseline*
3 Months 12 Months
Responders to Questionnaires
(N=1725)
Interviewed
(N=201)
Non-Responders
(N=922)
Responders to
Questionnaires (N=1486)
Interviewed
(N=329)
Non-Responders
(N=1033)
Age; mean (SD) 47.3 (13.3) (n=1725) 40.6 (12.5) (n=201) 40.3 (13.4) (n=922) 47.3 (13.0) (n=1486) 41.5 (13.1) (n=329) 41.6 (14.0) (n=1033)
Sex, female; n (%) 746 (43.3%) (n=1725) 60 (29.9%) (n=201) 361 (39.2%) (n=922) 636 (42.8%) (n=1486) 124 (37.7%) (n=329) 407 (39.4%) (n=1033)
Episode duration, >7 days; n (%) 911 (53.2%) (n=1714) 108 (54.0%) (n=200) 481 (52.6%) (n=914) 787 (53.2%) (n=1478) 174 (53.2%) (n=327) 539 (52.7%) (n=1023)
Use of medication, yes; n (%) 805 (52.0%) (n=1547) 43 (43.0%) (n=100) 193 (48.7%) (n=396) 694 (51.7%) (n=1343) 98 (49.2%) (n=199) 249 (49.7%) (n=501)
Back pain intensity, NRS
(0–10); mean (SD)
6.7 (2.0) (n=1695) 6.7 (2.1) (n=200) 6.7 (2.1) (n=896) 6.6 (2.0) (n=1461) 6.7 (2.1) (n=320) 6.7 (2.1) (n=1010)
Leg pain intensity, NRS
(0–10); mean (SD)
3.0 (3.0) (n=1700) 3.0 (2.7) (n=194) 2.9 (2.9) (n=889) 2.9 (2.9) (n=1466) 3.1 (2.9) (n=321) 3.0 (2.9) (n=996)
FABQ work subscale (0–42) 12.0 (9.0) (n=1417) 13.4 (9.4) (n=171) 13.6 (10.2) (n=763) 11.8 (8.9) (n=1243) 14.2 (10.5) (n=260) 13.3 (9.7) (n=848)
Activity limitation, RMDQ
(0–100)
54.8 (23.2) (n=1725) 56.9 (25.1) (n=201) 54.8 (24.7) (n=922) 54.7 (23.2) (n=1486) 56.0 (24.2) (n=329) 55.0 (24.6) (n=1033)
Note: *All except medication are from Baseline 1.
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evidence gaps related to management of LBP in
communities.
48
Among those were research into prognosis
of different LBP phenotypes, patient perceptions and beha-
viours, and social determinants of persistent LBP. Along
with our pre-determined domains, these and other research
questions can be addressed using this cohort alone or in
combination with information in Danish registries.
Conclusion
The Chiropractic low back pain Cohort (ChiCo) is a large
cohort of patients seeking care for LBP from primary care
chiropractors in Denmark. Participants were followed for
one year with good follow-up rates and a subset of partici-
pants had weekly follow-ups via SMS. A number of pre-
specied research areas of interest informed the choice of
the measured variables, and information in the database can
be linked at an individual level with the information-rich
Danish population-based registries. We invite researchers
interested in asking relevant questions from the ChiCo
data to collaborate with us on projects based on the cohort.
Data Sharing Statement
Application forms to use the described data for research
projects are available from the Nordic Institute of
Chiropractic and Clinical Biomechanics (Orla Lund Nielsen).
Ethics and Data Protection
The Health Research Ethics Committee for Southern
Denmark determined (S-20,162,000-109) that the project
did not require ethical approval according to Danish
regulations.
49
Questionnaire surveys and medical database
research projects only require notication to the research
ethics committee system if the project involves human
biological material. Storing and processing of personal
data was registered with the Danish Data Protection
Agency via the University of Southern Denmark’s joint
registration system (2015-57-0008), le no. 16/47,215.
The legal basis of the processing of personal data was
informed consent and complied with the European
General Data Protection Regulation (GDPR EU 2016/679)
Article 9, 2(a). Apart from stating their rights and describ-
ing the aim and setup of the cohort, the consent informed
potential participants that their treatment would not be
affected by participation and that the chiropractor would
not have access to their questionnaire responses. Besides
data collected directly from participants, consent also
allowed researchers to acquire relevant data from Danish
public registers, such as information on health-care
utilization. Without patients explicitly giving study consent,
it was technically impossible for them to enter any data.
Acknowledgment
The authors want to acknowledge participating patients,
clinic staff, and clinicians for taking part in establishing
the cohort. Thanks to research assistant Gitte Jakobsen
for day-to-day contact to the clinics and to OPEN patient
data Exploratory Network for access to REDCap and
technical support.
Author Contributions
All authors made a signicant contribution to the work
reported, whether that is in the conception, study design,
execution, acquisition of data, analysis and interpretation,
or in all these areas; took part in drafting, revising or
critically reviewing the article; gave nal approval of the
version to be published; have agreed on the journal to
which the article has been submitted; and agree to be
accountable for all aspects of the work.
Funding
Data collection and management of the database were
funded by the Danish Foundation for Chiropractic
Research and Post-graduate Education (le no.
RTLN5550–16/621). The conduct of the study was
nanced by a grant from The Foundation for
Chiropractic Research and Post-graduate Education.
Disclosure
AKs position at University of Southern Denmark is par-
tially funded by the Danish Fund for Chiropractic
Research and Postgraduate Education. TSJs position at
NIKKB is funded by the Danish Fund for Chiropractic
Research and Postgraduate Education. The authors report
no other potential conicts of interest for this work.
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