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: email@example.com. 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. 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