A Systematic Review of the Global Prevalence of Low Back Pain

 
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ARTHRITIS & RHEUMATISM
                                                                                                        Vol. 64, No. 6, June 2012, pp 2028–2037
                                                                                                        DOI 10.1002/art.34347
                                                                                                        © 2012, American College of Rheumatology

                A Systematic Review of the Global Prevalence of
                               Low Back Pain

   Damian Hoy,1 Christopher Bain,1 Gail Williams,1 Lyn March,2 Peter Brooks,3 Fiona Blyth,4
                  Anthony Woolf,5 Theo Vos,1 and Rachelle Buchbinder6

        Objective. To perform a systematic review of the                      gators are encouraged to adopt recent recommendations
global prevalence of low back pain, and to examine the                        for a standard definition of low back pain and to consult
influence that case definition, prevalence period, and                        a recently developed tool for assessing the risk of bias of
other variables have on prevalence.                                           prevalence studies.
        Methods. We conduced a new systematic review of
the global prevalence of low back pain that included                                 Low back pain is one of the most common health
general population studies published between 1980 and                         problems and creates a substantial personal, community,
2009. A total of 165 studies from 54 countries were                           and financial burden globally (1–4). As part of estimat-
identified. Of these, 64% had been published since the                        ing the global burden of low back pain, with low back
last comparable review.                                                       pain defined as “activity-limiting low back pain (⫹/⫺
        Results. Low back pain was shown to be a major                        pain referred into 1 or both lower limbs) that lasts for at
problem throughout the world, with the highest preva-                         least 1 day” (5), country-specific prevalence data were
lence among female individuals and those aged 40–80                           required.
years. After adjusting for methodologic variation, the                               The most recent global review of the prevalence
mean ⴞ SEM point prevalence was estimated to be                               of low back pain in the adult general population was
11.9 ⴞ 2.0%, and the 1-month prevalence was estimated                         published in 2000 and showed point prevalence of
to be 23.2 ⴞ 2.9%.                                                            12–33% and 1-year prevalence of 22–65% (6). Since
        Conclusion. As the population ages, the global                        then, 2 additional global reviews have been conducted,
number of individuals with low back pain is likely to                         one of which focused on the elderly (2) and the other on
increase substantially over the coming decades. Investi-                      adolescents (7). A key finding from these reviews was
                                                                              the extent of methodologic variation between studies,
         Supported by the Bill and Melinda Gates Foundation (to               especially regarding the case definition and prevalence
Dr. Hoy and Prof. Vos), the Australian Commonwealth Department                period used, and the nature and extent of measures
of Health and Ageing (to Prof. March), and the Australian National
Health and Medical Research Council (Postgraduate Scholarship
                                                                              taken to minimize bias (2,6–10).
569772 to Dr. Hoy and Practitioner Fellowships 334010 [2005–2009]                    Although these previous reviews made a major
and 606429 [2010–2014] to Prof. Buchbinder).                                  contribution to our understanding of low back pain, a
         1
           Damian Hoy, BAppSc, MPH, PhD, Christopher Bain,
MBBS, MPH, Gail Williams, PhD, MSc, Theo Vos, PhD, MSc: Uni-
                                                                              large number of prevalence studies have been published
versity of Queensland, Herston, Queensland, Australia; 2Lyn March,            subsequently. The specific aim of the current study was
MBBS, PhD, MSc: Royal North Shore Hospital, North Sydney Public               to perform an up-to-date systematic review of the global
Health Unit, Institute of Bone and Joint Research, and University
of Sydney, Sydney, New South Wales, Australia; 3Peter Brooks, MD,
                                                                              prevalence of low back pain for informing the Global
FRACP: University of Melbourne, Melbourne, Victoria, Australia;               Burden of Disease (GBD) study, and in doing so, to
4
  Fiona Blyth, MBBS, PhD, MPH, FAFPHM: University of Sydney,                  examine the influence that case definition, prevalence
Sydney, New South Wales, Australia; 5Anthony Woolf, MBBS, FRCP:
Peninsula College of Medicine and Dentistry, Plymouth, UK; 6Ra-
                                                                              period, and other variables have on prevalence.
chelle Buchbinder, MBBS, PhD, MSc, FRACP: Cabrini Medical Centre,
Malvern, Victoria, Australia, and Monash University, Melbourne,                                      METHODS
Victoria, Australia.
         Address correspondence to Damian Hoy, PhD, MPH, Uni-                         The methods used conformed to the Meta-analysis of
versity of Queensland, School of Population Health, Herston Road,             Observational Studies in Epidemiology (11) and the Cochrane
Herston, Queensland 4006, Australia. E-mail: d.hoy@uq.edu.au.                 Collaboration (12) recommendations.
         Submitted for publication May 10, 2011; accepted in revised                  Selection criteria. All population-based studies pub-
form December 15, 2011.                                                       lished from 1980 to 2009 in which the prevalence of low back

                                                                       2028
GLOBAL PREVALENCE OF LOW BACK PAIN                                                                                                2029

pain was reported were considered for inclusion. Studies were         Following discussion, agreement was reached for all differ-
excluded if they clearly were not representative of the general       ences. In the majority of instances, the initial assessment by
population (e.g., clinic patients, pregnant women, miners),           DH was confirmed by the consensus.
were limited to a subset of individuals with low back pain (e.g.,              Data preparation. Uncertainty for each estimate was
those with spondylolisthesis), had a sample size of ⬍150, or          recorded as a standard error. If an estimate was not reported,
were reviews.                                                         it was calculated from the reported confidence interval or
         Search strategy. The Ovid Medline, EMBase, and               sample size, as described in Appendix 2 (available at the
CINAHL electronic databases were searched. There were no              Arthritis & Rheumatism web site at http://onlinelibrary.
age, sex, or language restrictions. The terms “back pain,”            wiley.com/journal/10.1002/(ISSN)1529-0131). The database
“lumbar pain,” “back ache,” “backache,” and “lumbago” were            was screened for outliers, inconsistencies, and unexpected and
used individually and combined with each of the following:            missing values. Scatterplots were used to inspect the outliers.
“prevalence,” “incidence,” “cross-sectional,” and “epidemiol-         Outliers were subjectively defined as prevalence estimates that
ogy.” Reference lists of included studies were inspected to           appeared to be substantially outside the plausible range.
identify additional relevant studies. One reviewer (DH) as-           Outliers were excluded from the analysis if the study risk of
sessed the titles and abstracts of all retrieved references to        bias was moderate or high, and if data were available from
identify studies that appeared to fulfill the inclusion criteria,     another study in the same country with an equal or lower risk
and all potentially eligible articles were retrieved in full text.    of bias.
         Data extraction and management. The relevant study                    Assessment of heterogeneity. Heterogeneity between
information was extracted (by DH) into a Microsoft Excel              estimates was assessed using the I2 statistic (16). A value of
database (13). If a study presented age- and/or sex-specific          zero indicates true homogeneity, while values of 25%, 50%,
estimates, the total counts were not extracted. If data were          and 75% indicate low, moderate, and high heterogeneity,
stratified by age and sex separately, the total and sex-specific      respectively (17).
data were not extracted. Age/sex bands with sample sizes of                    Statistical analysis. Statistical analysis was performed
⬍50 were merged with one or more adjacent age/sex bands in            using Stata version 10.1 (18). The influence that individual and
the study. If a study presented both raw and standardized data,       summary risk-of-bias items, case definition, prevalence period,
standardized data were ignored; if a study presented only             sex, age, year of data collection, urbanicity, and economy have
standardized data, these were extracted. Case definitions were        on prevalence was assessed using pairwise correlations for
partitioned as follows: anatomic area, minimum episode dura-          continuous variables, t-tests for independent samples for bi-
tion, and whether or not cases had to have activity limitation.       nary variables, and one-way analysis of variance for variables
         Variables extracted included the following: region,          with multiple categories to detect differences between groups.
country, year of publication, citation, study type, data ascer-       In a multivariate regression analysis, data were log trans-
tainment, sample size, case definition (overall), case definition     formed to achieve normality, using the following formula:
(anatomic), case definition (minimum episode duration), case          log(prevalence ⫹ 0.2). The value 0.2 was chosen, because it
definition (activity limitation), coverage, urbanicity, each item     provided the best approximation to normality. The outcome
from the risk-of-bias tool, year start of data collection, year end   variable was “overall prevalence of low back pain” and was
of data collection, prevalence period, age, sex, denominator          unrestricted by prevalence period. The standard error was
(number of cases at risk), numerator (number of cases with low        calculated using the formula (19): SE(log[prevalence ⫹ 0.2]) ⫽
back pain), prevalence, standard error (SE), design effect, and       (SE[prevalence])/(prevalence ⫹ 0.2). Linear, quadratic, and
whether data were standardized. Double entry of data took             cubic associations of prevalence with age were assessed by
place for a randomly selected sample of the studies (10% [n ⫽         including the midpoint of the age group, centered age squared,
16]) and demonstrated a high level of accuracy (99.4%). The 8         and centered age cubed in the multivariate model.
inaccuracies related to text fields (e.g., incorrect spelling) did             The centered age squared and centered age cubed
not influence the numerical data.                                     were calculated by taking the average of all midpoints of the
         Risk of bias assessment. One reviewer (DH) assessed          age groups and subtracting this value from each midpoint of
the risk of bias for each included study, using a tool that was       the age group to derive a centered age value, which was then
developed for this purpose and was shown to be reliable (14).         squared and cubed, respectively. Midpoints of the age groups
The tool includes 10 items that assess measurement bias,              were categorized as follows: 0–9, 10–19, . . . , and 90–99.
selection bias, and bias related to the analysis (all rated as        Prevalence trends over time were assessed using a pairwise
either high or low risk) and an overall assessment of risk of bias    correlation t-test for independent samples to compare data
rated as either low, moderate, or high risk (see Appendix 1,          collected before 1998 with data collected during or after 1998.
which is available at the Arthritis & Rheumatism web site at          The influence of economic status on prevalence was assessed
http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1529-            by grouping countries according to the World Bank income
0131).                                                                group classification system (20) and performing a t-test for
         A second reviewer (RB) assessed the risk of bias on a        independent samples. A pairwise comparison was undertaken
sample of 16 studies (10%) to ensure that the criteria were           to compare the Human Development Index with prevalence
applied consistently and that consensus could be reached, as          (21).
recommended by the Cochrane Handbook for Systematic Re-                        The quality of the overall evidence from the systematic
views of Interventions (15). Overall agreement between the            review was summarized using the GRADE (Grading of Rec-
reviewers was 78% with a kappa value of 0.69 (95% confidence          ommendations Assessment, Development and Evaluation) sys-
interval 0.55, 0.79), indicating moderate agreement (kappa            tem (15,22), which has the following options: 1) high quality—
values from 0.41 to 0.60 indicate moderate agreement, and             further research is very unlikely to change our confidence in
values from 0.61 to 0.80 indicate substantial agreement).             the estimate, 2) moderate quality—further research is likely to
2030                                                                                                                          HOY ET AL

                                                                            moval of estimates with a prevalence period of ⬎1 year. In
                                                                            addition, to attempt to control for some of the methodologic
                                                                            heterogeneity, a prediction of the overall mean prevalence
                                                                            estimate was made by including the following variables in a
                                                                            multivariate regression model: sex, midpoint of age group,
                                                                            centered age squared, centered age cubed, prevalence period,
                                                                            anatomic case definition, minimum episode duration, activity
                                                                            limitation, coverage, urbanicity, and the 10 individual risk-of-
                                                                            bias items. The resulting estimates were for the national-level
                                                                            mean point and 1-month prevalence of activity-limiting low
                                                                            back pain lasting for more than 1 day on the “posterior aspect
                                                                            of the body from the lower margin of the twelfth ribs to the
                                                                            lower gluteal folds” (5).

                                                                                                        RESULTS
                                                                                    Search results. The electronic database search
                                                                            yielded 8,727 studies (Figure 1). Irrelevant titles (n ⫽
Figure 1. Search strategy and exclusion process for studies of the          8,211) were excluded, leaving 516 eligible titles. Of
prevalence of low back pain. ⴱ ⫽ study not representative of the            these, 139 abstracts met the inclusion criteria. An addi-
national population (n ⫽ 331), study focused on a specific subset of low
                                                                            tional 20 eligible studies were identified from inspection
back pain (n ⫽ 16), sample size less than 150 (n ⫽ 15), or review article
(n ⫽ 15). † ⫽ Article did not exist (n ⫽ 2) or journal was no longer in     of the reference lists of included studies. Nine full-text
circulation, and attempts to retrieve the article through a document        articles could not be located, leaving 150 studies that
delivery service and/or directly from the author were unsuccessful (n ⫽     met the inclusion criteria. Two German studies (one
7).                                                                         with a high risk of bias and one with a moderate risk of
                                                                            bias) (23,24) were excluded, because their prevalence
                                                                            estimates were considered to be outliers (point preva-
have an important impact on our confidence in the estimate
and may change the estimate, 3) low quality—further research                lence ranged from 76% to 92% in elderly Germans).
is very likely to have an important impact on our confidence in             Two other German studies (one with a moderate risk of
the estimate and is likely to change the estimate, and 4) very              bias and one with a low risk of bias) had estimates (point
low quality—any estimate is very uncertain.                                 prevalence ranging from 20% to 50%) that were more in
         Sensitivity and predictive analyses. Three prespecified
sensitivity analyses were undertaken to assess their impact on              keeping with those of most other studies (25,26). Of the
the estimates, as follows: 1) removal of high risk-of-bias                  remaining studies, one contained data from studies in 17
estimates, 2) removal of standardized estimates, and 3) re-                 countries (27), and the other contained data from stud-

Table 1.   Prevalence of low back pain according to prevalence period and case definition variations
                                                                                        Quantile
                                                 No. of
             Prevalence                         estimates          10%       25%          50%           75%        90%        Mean ⫾ SD%
Prevalence period
  Point                                            243              6.3      10.3          15.0         24.2       35.5         18.3 ⫾ 11.7
  1 month                                          145             14.8      21.3          32.1         38.0       49.0         30.8 ⫾ 12.7
  1 year                                           271             14.3      21.0          37.4         53.0       64.8         38.0 ⫾ 19.4
  Lifetime                                         133              6.2      15.1          42.0         60.4       66.4         38.9 ⫾ 24.3
Anatomic
  Back                                             268              9.9      15.8          26.6         36.4       53.6         28.5 ⫾ 16.4
  Low back                                         302              7.2      12.8          26.1         43.1       56.0         29.1 ⫾ 18.8
  R12 to lower GFs*                                254             11.0      17.4          35.2         52.0       63.7         35.5 ⫾ 19.7
Minimum episode duration
  Not specified                                    661              8.7      15.0          31.5         48.8       62.5         33.2 ⫾ 20.3
  1 day                                            146             14.1      22.1          34.0         44.0       56.4         33.8 ⫾ 15.8
  3 months/“chronic”                                86              8.7      12.8          19.2         24.3       33.6         20.1 ⫾ 9.8
Activity limitation
  With or without activity limitation              912               9.1     15.8          29.1         45.5       58.2         31.8 ⫾ 19.0
  Activity-limiting only                            54               5.0      8.1          12.2         18.8       30.8         17.0 ⫾ 15.4

* Posterior aspect of the body from the lower margin of the twelfth ribs (R12) to the lower gluteal folds (GFs).
GLOBAL PREVALENCE OF LOW BACK PAIN                                                                                           2031

          Table 2. Results of multivariate regression analysis*
                                                                    Regression
                             Covariate                              coefficient              95% CI                  P
          Constant                                                     ⫺1.58              ⫺1.75, ⫺1.41            ⬍0.001
            Sex
              Female                                                    0
              Unspecified                                              ⫺0.06              ⫺0.11, ⫺0.01             0.011
              Male                                                     ⫺0.11              ⫺0.15, ⫺0.07            ⬍0.001
            Age
              Midpoint                                                 ⬍0.01              ⬍0.01, 0.01             ⬍0.001
              Centered age squared                                     ⬍0.01              ⬍0.01, ⬍0.01            ⬍0.001
              Centered age cubed                                       ⬍0.01              ⬍0.01, ⬍0.01             0.147
            Prevalence period
              Point                                                      0
              1 month                                                    0.30               0.24, 0.36            ⬍0.001
              1 year                                                     0.45               0.40, 0.49            ⬍0.001
              Lifetime                                                   0.49               0.43, 0.55            ⬍0.001
            Anatomic case definition
              Back                                                       0
              Low back                                                   0.06               0.01, 0.11             0.029
              R12 to lower GFs†                                          0.56               0.45, 0.67            ⬍0.001
            Minimum episode duration
              Not specified                                             0
              1 day                                                    ⫺0.10              ⫺0.15, ⫺0.04            ⬍0.001
              3 months/“chronic”                                       ⫺0.28              ⫺0.37, ⫺0.19            ⬍0.001
            Activity limitation
              With or without activity limitation                       0
              Activity-limiting only                                   ⫺0.20              ⫺0.29, ⫺0.10            ⬍0.001
            Coverage
              Community                                                 0
              Regional                                                 ⫺0.02              ⫺0.10, 0.05              0.510
              National                                                 ⫺0.19              ⫺0.29, ⫺0.08            ⬍0.001
            Urbanicity
              Rural                                                      0
              Urban                                                      0.04             ⫺0.03, 0.12               0.256
            Risk of bias item 1, target population
              Low risk                                                  0
              High risk                                                ⫺0.07              ⫺0.14, 0.01               0.071
            Risk of bias item 2, sampling frame
              Low risk                                                   0
              High risk                                                  0.03             ⫺0.05, 0.12               0.457
            Risk of bias item 3, random selection
              Low risk                                                   0
              High risk                                                  0.11             ⫺0.01, 0.23               0.066
            Risk of bias item 4, nonresponse bias
              Low risk                                                  0
              High risk                                                ⫺0.04              ⫺0.08, 0.00               0.079
            Risk of bias item 5, was a proxy used?
              Low risk                                                  0
              High risk                                                ⫺0.51              ⫺0.62, ⫺0.40            ⬍0.001
            Risk of bias item 6, case definition
              Low risk                                                   0
              High risk                                                  0.44               0.35, 0.53            ⬍0.001
            Risk of bias item 7, study instrument
              Low risk                                                   0
              High risk                                                  0.12               0.07, 0.16            ⬍0.001
            Risk of bias item 8, data collection mode
              Low risk                                                   0
              High risk                                                  0.47               0.34, 0.60            ⬍0.001
            Risk of bias item 9, prevalence period
              Low risk                                                  0
              High risk                                                ⫺0.07              ⫺0.15, 0.00               0.050
            Risk of bias item 10, numerator/denominator
              Low risk                                                   0
              High risk                                                  0.01             ⫺0.18, 0.20               0.913
          * Values were log transformed to achieve normality (see Methods). 95% CI ⫽ 95% confidence interval.
          † Posterior aspect of the body from the lower margin of the twelfth ribs (R12) to the lower gluteal folds (GFs).
2032                                                                                                              HOY ET AL

                                                                   indicating high heterogeneity, and additional stratifica-
                                                                   tion by prevalence period and varying case definitions
                                                                   had only a minor impact on reducing the I2 value (to
                                                                   99.1%). Multivariate regression showed that several
                                                                   study-level variables had a significant influence on prev-
                                                                   alence (Table 2).
                                                                           Risk of bias. Five of the 10 individual risk-of-bias
                                                                   items were shown to significantly influence prevalence
                                                                   (Table 2). A high risk of bias for 3 items (case definition
                                                                   [item 6], whether the study instrument had been tested
                                                                   for reliability and validity [item 7], and comparability of
                                                                   mode of data collection [item 8]) was associated with a
                                                                   higher prevalence, while high risk of bias for 2 items
                                                                   (whether the data were collected directly from subjects
                                                                   as opposed to a proxy [item 5] and prevalence period
                                                                   [item 9]) was associated with a lower prevalence.
Figure 2. Median prevalence of low back pain, with interquartile
range, according to prevalence period.
                                                                           Case definition. Most estimates (n ⫽ 661) did not
                                                                   specify the minimum episode duration required for a
                                                                   case to be counted (Table 1). Of those that did specify
ies in 2 countries (23). Thus, a total 165 studies provided        the minimum duration, the most common durations
966 age- or sex-specific prevalence estimates for 54               were 1 day (n ⫽ 146), 3 months (n ⫽ 38), and 1 week
countries.                                                         (n ⫽ 34). In addition, 48 estimates specified that disease
        Description of included studies. An overview of            “chronicity” was required for inclusion. For estimates in
the included studies is provided in Appendix 3 (available          which the minimum episode duration was not specified,
at the Arthritis & Rheumatism web site at http://                  the mean prevalence was significantly higher than that
onlinelibrary.wiley.com/journal/10.1002/(ISSN)1529-                for estimates for which durations were specified as 1 day
0131). All of the included studies had cross-sectional             (T ⫽ ⫺3.73, P ⬍ 0.001) and 3 months/“chronic” (T ⫽
designs and ascertained data through an interview or               ⫺6.61, P ⬍ 0.001).
self-completed questionnaire. The majority of studies                      For anatomic locations, the “low back” was the
included both sexes, a broad age range in the adult                most common category (n ⫽ 302), followed by the
population, and both urban and rural populations. Of               “back” (n ⫽ 268), and the “posterior aspect of the body
the 966 estimates, 161 were standardized by age, sex,              from the lower margin of the twelfth ribs to the lower
and/or some other factor. The mean year of publication             gluteal folds” (n ⫽ 254) (Table 1). Prevalence differed
was 1999 (median 2000 [range 1982–2009]), and 64% of               significantly across anatomic definitions (F ⫽ 20.91, P ⬍
the studies had been published since the last comparable           0.001); the definitions of “low back” (T ⫽ 2.05, P ⫽
systematic review (6). Overall, 36 studies (22%) were              0.041) and “posterior aspect of the body from the lower
rated as having a low risk of bias (353 estimates), 82             margin of the twelfth ribs to the lower gluteal folds”
(50%) were rated as having a moderate risk of bias (434            (T ⫽ 10.52, P ⬍ 0.001) were associated with significantly
estimates), and 47 (28%) were rated as having a high risk          higher mean prevalence compared with the “back.”
of bias (179 estimates). High risk-of-bias ratings were                    Only a small proportion of the estimates were
most common for item 1 (national representativeness/               restricted to activity-limiting cases (n ⫽ 54) (Table 1).
target population), item 4 (nonresponse bias), item 6              The mean prevalence of activity-limiting low back pain
(case definition), and item 7 (study instrument) (see              was approximately half that of low back pain with or
Appendix 4 and Appendix 5 [which shows the risk of bias            without activity limitation (T ⫽ 5.63, P ⬍ 0.001). Activity
ratings for all included studies], available at the Arthritis      limitation continued to be significantly related to prev-
& Rheumatism web site at http://onlinelibrary.wiley.com/           alence in the multivariate regression analysis (T ⫽
journal/10.1002/(ISSN)1529-0131).                                  ⫺4.02, P ⬍ 0.001).
        Key results. The mean overall prevalence of low                    Prevalence period. The most common prevalence
back pain, which was defined as all prevalence regardless          periods were point (n ⫽ 243), 1 month (n ⫽ 145), 1 year
of prevalence period, was 31.0%. The mean point prev-              (n ⫽ 271), and lifetime (n ⫽ 133) (Table 1). Prevalence
alence was 18.3%, and 1-year prevalence was 38.0%                  differed significantly according to prevalence period
(Table 1). For prevalence plotted by age, I2 ⫽ 99.6%,              (F ⫽ 29.15, P ⬍ 0.001). The mean point prevalence
GLOBAL PREVALENCE OF LOW BACK PAIN                                                                                               2033

                                                                          with males (T ⫽ 2.31 [P ⫽ 0.022] and T ⫽ 2.26 [P ⫽
                                                                          0.025], respectively), but there was no significant differ-
                                                                          ence between the sexes for 1-year prevalence and life-
                                                                          time prevalence.
                                                                                  A cubic representation of the age curve provided
                                                                          the best fit to prevalence. Both the mean prevalence and
                                                                          the median prevalence were high during adolescence,
                                                                          declined among those ages 20–29 years, progressively
                                                                          increased until peaking somewhere between 40 and 69
                                                                          years (this peak occurred earlier for men than women),
                                                                          and then progressively declined (Figure 3). However, the
                                                                          difference in mean prevalence between adolescents and
                                                                          individuals ages 20–29 years was not significant, whereas
                                                                          there were significant differences between those ages
                                                                          20–29 years and those ages 40–69 years (T ⫽ ⫺3.18, P ⫽
Figure 3. Median prevalence of low back pain, with interquartile
range, according to sex and midpoint of age group. Midpoint ⫽ (lower
                                                                          0.002) and between individuals ages 40–69 years and
limit of age group ⫹ [upper limit of age group – lower limit of age       those ages 80–99 years (T ⫽ 3.14, P ⫽ 0.002).
group]/2).                                                                        The regression analysis showed that the quadratic
                                                                          association with age was more significant than the cubic
                                                                          and linear associations. That is, the association charac-
(18.3%) was significantly lower than the 1-month prev-                    terized by increasing prevalence until middle age fol-
alence (30.8%) (T ⫽ ⫺9.8, P ⬍ 0.001), and the 1-month                     lowed by a decline during older age was more significant
prevalence was significantly lower than the 1-year prev-                  than those characterized by gradually increasing preva-
alence (38.0%) (T ⫽ ⫺4.0, P ⫽ 0.001) (Figure 2). There                    lence across all ages (T ⫽ 4.36, P ⬍ 0.001) and increas-
was no significant difference between the 1-year preva-                   ing prevalence in adolescence, followed by a decline in
lence and the lifetime prevalence (38.9%). Regression                     the 20s, an increase during middle age, and a decline
analysis demonstrated that 1-month, 1-year, and lifetime                  during the oldest ages (T ⫽ 1.45, P ⫽ 0.147). This
prevalences were all significantly higher than the point                  remained so when the analysis was limited to point
prevalence (Table 2).                                                     prevalence estimates.
        Sex and age. The median overall prevalence of                             Year, urbanicity, and economy. The prevalence
low back pain was higher among females than among                         of low back pain increased very slightly over the past 3
males across all age groups (Figure 3). The overall mean                  decades (r ⫽ 0.096, P ⫽ 0.003). There was no significant
prevalence of low back pain was significantly higher                      difference in the mean prevalence between urban and
among females compared with males (Table 3) (T ⫽ 4.1,                     rural areas (Table 3). The mean prevalence in countries
P ⬍ 0.001), and this difference continued to be evident                   with high-income economies was higher than estimates
in the regression analysis (T ⫽ 6.04, P ⬍ 0.001). Both the                from countries with middle-income (T ⫽ 5.09, P ⬍
mean point prevalence and the mean 1-month preva-                         0.001) and low-income economies (T ⫽ 3.03, P ⫽ 0.003).
lence were significantly higher among females compared                    There was no significant difference in mean prevalence

                Table 3.   Prevalence of low back pain according to sex, urbanicity, and economy
                                                                           Quantile
                                          No. of
                    Prevalence           estimates      10%        25%       50%        75%        90%    Mean ⫾ SD%
                Sex
                  Female                   344           12.5      21.0      33.7       48.1       64.0    35.3 ⫾ 18.8
                  Male                     323            7.8      15.0      25.9       40.0       56.5    29.4 ⫾ 18.5
                Urbanicity
                  Rural                     62            1.8      13.1      31.1       45.2       63.0    31.9 ⫾ 21.8
                  Urban                    270            7.2      14.2      25.3       44.3       62.1    30.7 ⫾ 20.4
                Economy
                  Low income                13            0.5       0.8      18.2       21.7       25.9    16.7 ⫾ 15.7
                  Middle income            216            5.2      10.6      21.4       38.6       52.0    25.4 ⫾ 18.3
                  High income              737           10.3      16.9      30.3       46.6       60.9    32.9 ⫾ 19.0
2034                                                                                                           HOY ET AL

between middle-income and low-income economies.                tivity analysis was performed to assess the impact of
There was a strong positive correlation between a coun-        including estimates with a high risk of bias (11,12,28).
try’s Human Development Index and overall mean                 The sensitivity analysis showed that the overall mean
prevalence (r ⫽ 0.088, P ⬍ 0.001), and this continued to       prevalence would have been significantly higher if esti-
be significant when the analysis was limited to point          mates with a high risk of bias had been excluded. In
prevalence estimates (r ⫽ 0.122, P ⫽ 0.023).                   addition, 5 of the 10 individual items on the risk of bias
        Quality of overall evidence. The quality of the        tool had a significant influence on prevalence. These
overall evidence from this review was moderate; that is,       findings provide empirical data about the direction of
further research is likely to have an important impact on      the bias and its potential effect.
our confidence in the estimate and may change the                      We observed a substantial increase in the number
estimate.                                                      of studies of low back pain prevalence since the last
        Sensitivity and predictive analyses. Excluding         comparable review (6). Similar to other reviews, we
high risk-of-bias estimates from the analysis resulted in a    observed considerable methodologic variation between
significant increase in the overall mean prevalence, from      studies, which particularly related to the prevalence
31.0% to 32.7% (T ⫽ 2.64, P ⫽ 0.008) and a nonsignif-          period and case definition (2,6,9,29). A standardized
icant increase in point prevalence, from 18.3% to 18.7%.       definition of low back pain will assist future reviews,
Excluding standardized data resulted in nonsignificant         enable greater comparisons between countries, and ul-
increases in overall prevalence (to 31.1%) and point           timately lead to a far-improved understanding of low
prevalence (to 18.7%). If estimates associated with            back pain.
prevalence periods longer than 1 year (5 years and                     Dionne et al (30) recommended using the follow-
lifetime) were excluded, the overall prevalence de-            ing questions in prevalence studies of low back pain: 1)
creased significantly to 29.7% (T ⫽ ⫺2.02, P ⫽ 0.044).         In the past 4 weeks, have you had pain in your low back?
        When the regression analysis results were used to      and 2) If yes, was this pain bad enough to limit your
adjust the overall mean ⫾ SD prevalence (31.0 ⫾ 0.6%)          usual activities or change your daily routine for more
to reflect our GBD 2010 study case definition for low          than one day? Those investigators emphasized the im-
back pain (activity-limiting low back pain lasting more        portance of describing the specific anatomic area and,
than 1 day on the “posterior aspect of the body from the       when possible, using a diagram of the body with the low
lower margin of the twelfth ribs to the lower gluteal          back area shaded. The area they recommend for the low
folds”), point prevalence was reduced to 11.9 ⫾ 2.0%,          back is “the posterior aspect of the body from the lower
and 1-month prevalence was reduced to 23.2 ⫾ 2.9%.             margin of the twelfth ribs to the lower gluteal folds”
These values were also lower than the unadjusted               (30). Given that low back pain is quite common, point
mean ⫾ SD estimates for point prevalence (18.3 ⫾               prevalence estimates are also useful to capture and are
0.8%) and 1-month prevalence (30.8 ⫾ 1.1%). P values           easily interpreted by policy-makers.
less than 0.05 were considered significant.                            In addition, a detailed description of the study
                                                               population aids the validity of comparisons between
                                                               populations. Factors of interest include age, sex, history
                      DISCUSSION
                                                               of low back pain, occupation, job satisfaction, educa-
        Our updated systematic review of the global            tional status, stress, anxiety, depression, social support in
prevalence of low back pain showed that low back pain          the workplace, body mass index, and family history of
is a major problem throughout the world and is most            low back pain (31).
prevalent among females and persons ages 40–80 years.                  Consistent with other research, we observed a
After adjusting for methodologic variation, the mean ⫾         higher mean and median prevalence of low back pain
SD point prevalence of activity-limiting low back pain         among females compared with males (9,32). Possible
lasting more than 1 day was estimated to be 11.9 ⫾ 2.0%,       explanations for this difference include 1) pain related to
and the 1-month prevalence was estimated to be 23.2 ⫾          osteoporosis (33), menstruation (34–36), or pregnancy
2.9%. Due to significant methodologic heterogeneity            (37–39), 2) individual or societal influences resulting in
between the included studies, single summary measures,         sex differences in the likelihood of reporting somatic
such as mean prevalence, should be interpreted with            symptoms (32,40,41), and 3) the divergent growth pat-
caution.                                                       terns between the sexes during adolescence, which may
        This systematic review of the global prevalence of     influence pain in this period (7).
low back pain is the first to assess the risk of bias in the           We observed that the prevalence of low back pain
included studies and is the first study in which a sensi-      was high during adolescence, which concurs with a
GLOBAL PREVALENCE OF LOW BACK PAIN                                                                                  2035

previous review showing that the prevalence of low back      can greatly add to the challenge of publishing academi-
pain increases throughout adolescence, and this peak         cally rigorous studies.
often appears earlier in girls than in boys, possibly as a           The mean lifetime prevalence of low back pain
result of an earlier onset of puberty (7). In our review,    (38.9%) was much lower than expected and was partic-
the prevalence of low back pain was highest during           ularly influenced by low rates from studies conducted in
middle age, which represents some of the most produc-        China (46–48), Nepal (49), Cuba (50), and Pakistan
tive years of a person’s working life. This results in a     (51). The low prevalence of low back pain observed in
major economic impact for many individuals, families,        these countries with low-income and middle-income
businesses, and governments (42–44).                         economies may have several influences, some of which
        A curvilinear distribution of the prevalence of      were discussed earlier. In addition, chronic low back
low back pain over age was also reported in a review by      pain may make up a larger proportion of all low back
Dionne et al (2). Those investigators demonstrated that      pain in these countries, making the ratio of lifetime
this was apparent for all low back pain; however, when       prevalence to other prevalence periods lower in these
they restricted their analysis to more severe forms of low   countries compared with countries with high-income
back pain, they observed that the prevalence kept in-        economies. Although no data support this, a study in
creasing in the older age groups. Consistent with these      Tibet showed a relatively low ratio of 1-year–to–point
findings, there is some evidence that older individuals      prevalence (42%:34%), suggesting that a high propor-
have a greater threshold for lower levels of pain but a      tion cases of low back pain are chronic in nature (52).
reduced tolerance to more severe pain (45).                  The relatively low lifetime prevalence observed in these
        Dionne et al (2) suggested that many factors         studies may also be attributable to selection, measure-
could explain the decrease in the prevalence of less         ment, and recall bias.
                                                                     Similar to most systematic reviews, our study is
severe low back pain that occurs with aging, including
                                                             likely to be subject to publication bias that may have
cognitive impairment, depression, decreased pain per-
                                                             inflated the prevalence estimates of low back pain (53).
ception, and increased tolerance to pain. In addition,
                                                             We attempted to limit the potential for publication bias
surveys often exclude persons living in institutions such
                                                             by conducting an extensive search for potentially rele-
as nursing homes (9), and these individuals may have a
                                                             vant studies and placing a specific focus on capturing
higher prevalence of low back pain compared with older
                                                             information from countries with low-income or middle-
persons living in the community.
                                                             income economies. In addition, we carefully examined
        Despite an increase in the amount of data since
                                                             the risk of bias for each included estimate.
earlier reviews (6,10), there continues to be a paucity of           Based on the results of this systematic review, low
information on low back pain in countries with low-          back pain continues to be a very common problem
income and middle-income economies. Our data are             globally. With aging populations, the absolute number of
consistent with a previous review showing that low back      people with low back pain is likely to increase substan-
pain was less prevalent in countries with low-income and     tially over the coming decades. Further research is
middle-income economies compared with countries with         needed to identify risk factors and culturally appropriate
high-income economies (10). The lower prevalence of          interventions to prevent and treat low back pain. Re-
low back pain in developing countries has been specu-        searchers are encouraged to adopt recent recommenda-
lated to be attributable to higher levels of exercise,       tions on defining low back pain in epidemiologic studies
shorter height, higher pain thresholds, and less access to   to assist future reviews, enable comparisons between
industrial insurance compared with countries with high-      countries, and improve our understanding of low back
income economies (10).                                       pain. Furthermore, the tool for assessing the potential
        Methodologic issues are also likely to explain       risk of bias of included estimates could be used to
some of this difference, including survey planning meth-     improve the design of future epidemiologic studies.
ods and differing case definitions and sample population
age and sex structures. Related to this, researchers from
                                                                             ACKNOWLEDGMENTS
countries with low-income and middle-income econo-
mies may, in some cases, experience greater barriers in             We would like to thank the following individuals who
trying to publish studies. For example, the majority of      were kind enough to provide us with data upon request:
                                                             Professor Fereydoun Davatchi, Dr. Arash Tehrani, Dr.
peer-reviewed journals accept submissions only in Eng-       Rowsan Ara, and Professor Atiqul Haq. In addition, we are
lish. Moreover, difficulties in constructing accurate sam-   thankful to Dr. Emma Smith for her work on the GBD 2010
pling frames and accessing remote regions and villages       study, Dr. Karla Meursing for translating a number of the
2036                                                                                                                                HOY ET AL

articles, Dr. Rungthip Puntumetakul, Melinda Protani, and Dr.                16. Higgins J, Thompson S. Quantifying heterogeneity in a meta-ana-
Rumna De for their involvement in testing of the risk-of-bias                    lysis. Stat Med 2002;21:1539–58.
tool, and Karen Carter and Dr. Linda Cobiac for their useful                 17. Huedo-Medina TB, Sanchez-Meca J, Marin-Martinez F, Botella J.
insights.                                                                        Assessing heterogeneity in meta-analysis: Q statistic or I2 index?
                                                                                 Psychol Methods 2006;11:193–206.
                                                                             18. Stata statistical software: release 10.1. College Station (TX):
                  AUTHOR CONTRIBUTIONS                                           StataCorp; 2009.
                                                                             19. Scheffe H. The analysis of variance. New York: Wiley & Sons;
          All authors were involved in drafting the article or revising it       1959.
critically for important intellectual content, and all authors approved      20. World Bank. Country classifications. World Bank; 2010. URL:
the final version to be published. Dr. Hoy had full access to all of the         http://data.worldbank.org/about/countryclassifications.
data in the study and takes responsibility for the integrity of the data     21. United Nations Development Programme. Human Development
and the accuracy of the data analysis.                                           Report 2010. New York: United Nations; 2010. URL: http://
Study conception and design. Hoy, Bain, Williams, March, Brooks,                 hdr.undp.org/en/reports/global/hdr2010/.
Blyth, Woolf, Vos, Buchbinder.                                               22. Guyatt GH, Oxman AD, Vist GE, Kunz R, Falck-Ytter Y,
Acquisition of data. Hoy, March, Blyth.                                          Alonso-Coello P, et al. GRADE: an emerging consensus on rating
Analysis and interpretation of data. Hoy, Bain, Williams, March,                 quality of evidence and strength of recommendations. BMJ 2008;
Brooks, Blyth, Woolf, Vos, Buchbinder.                                           336:924–6.
                                                                             23. Raspe H, Matthis C, Croft P, O’Neill T, for the European
                                                                                 Vertebral Osteoporosis Study Group. Variation in back pain
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