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Abstract
Background Musculoskeletal (MSK) diseases are expected to have a growing impact worldwide.
Objective To analyse the worldwide burden of MSK diseases from 2000 to 2015.
Methods Disability-adjusted life years (DALYs), which combines the years of life lost (YLLs) and the years lived with disability (YLDs), were extracted for 183 countries from the WHO Global Health Estimates Database. We analysed the median proportion of DALYS, YLLs and YLDs for MSK diseases (ICD-10: M00–M99) among the 23 WHO categories of diseases. Mixed models were built to assess temporal changes.
Results Worldwide, the total number of MSK DALYs increased significantly from 80,225,634.6 in 2000 to 107,885,832.6 in 2015 (p < 0.001), with the total number of MSK YLDs increasing from 77,377,709.4 to 103,817,908.4 (p = 0.0008) and MSK diseases being the second cause of YLDs worldwide. YLLs due to MSK diseases increased from 2,847,925.2 to 4,067,924.2 (p = 0.03). In 2015, the median proportion of DALYs attributed to MSK diseases was 6.66% (IQR: 5.30 – 7.88) in Europe versus 4.66% (3.98 – 5.59) in the Americas (p < 0.0001 vs Europe), 4.17% (3.14 – 6.25) in Asia (p < 0.0001), 4.14% (2.65 – 5.57) in Oceania (p = 0.0008) and 1.33% (1.03 – 1.92) in Africa (p < 0.0001). We observed a significant correlation (r = 0.85, p < 0.0001) between the proportion of MSK DALYs and the gross domestic product per capita for the year 2015.
Conclusions The burden of MSK diseases increased significantly between 2000 and 2015 and is high in Europe. These results are crucial to health professionals and policy makers to implement future health plan adjustments for MSK diseases.
- rheumatology
- global burden of disease
- daly
- YLL
- YLD
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Key messages
What is already known about this subject?
The burden of musculoskeletal (MSK) diseases is expected to increase worldwide
What does this study add?
The burden of MSK diseases has increased significantly between 2000 and 2015, with MSK diseases being the second cause of years lived with disability (YLDs) worldwide
The burden of MSK diseases is significantly higher in Europe than in all other continents.
MSK burden is strongly correlated with countries' gross domestic product per capita
How might this impact on clinical practice or future developments?
These results are crucial to inform health professionals, policy makers and national healthcare systems for the implementation of future health-plan adjustments.
Introduction
Musculoskeletal (MSK) diseases, defined as diseases which affect the locomotor system including muscles, bones, joints, tendons and ligaments, have a growing impact worldwide.1 This impact is measurable using disability-adjusted life years (DALYs), which combine the years lived with disability (YLDs) and the years of life lost (YLLs) through premature death. Previous studies have suggested a high prevalence and high disability linked to selected MSK diseases.2–8 However, representative data for the impact of MSK diseases as a whole are lacking, considering that osteoarthritis and low back pain are significantly more common than most inflammatory diseases.9 The economic burden of MSK diseases has been well described,5 but national healthcare systems tend to underestimate the role of MSK diseases owing to their low death rate.10 Importantly, the overall MSK burden is expected to increase, owing to the increase in average life expectancy11 and because many degenerative MSK diseases are considered largely irreversible.10 The low death rate and irreversibility may reduce the relative importance of MSK diseases to national healthcare systems and policy makers, compared with other categories of diseases such as cancers or cardiovascular diseases.
This study aimed to analyse the global burden of MSK diseases compared with other causes of morbidity-mortality, and its change over time, using data from a large publicly available WHO database.12 We also sought to analyse the socioeconomic determinants of this burden, by analysing its association with countries' gross domestic product (GDP) per capita.13 These results are crucial to rheumatologists, enabling a better understanding of the burden associated with MSK diseases, but also vital for policy makers and national healthcare systems to implement adjustments to future health plans.
Methods
DALYs, YLLs and YLDs
The DALY Index is a summary measure which combines time lost through premature death, YLLs, and time lived in states of less than optimal health, loosely referred to as 'disability', year lived with disability (YLDs).14 One DALY can be thought of as one lost year of 'healthy' life. DALYs for a specific cause are calculated as the sum of the YLLs from that cause and the YLDs for people living in states of less than good health resulting from a specific cause. The methodological details for calculation of the estimates used in this study are available online.15
Data sources and comparison of MSK with other categories of disease
We extracted the DALYs, YLDs and YLLs for the 183 countries from the WHO Global Health Estimates Database (publicly available online12). This provides detailed information about those three indicators from the year 2000 onwards. In this database, conditions are aggregated in 23 categories (eg, infectious and parasitic diseases, cardiovascular diseases, malignant neoplasms, musculoskeletal diseases, etc.) based on the International Classification of Diseases 10th revision (ICD-10). MSK diseases are defined as the ICD-10 codes M00 to M99.15
To analyse the socioeconomic determinants of MSK diseases, we correlated each country DALYs with its GDP per capita (in US dollars), available from a publicly available source.13
Statistical analysis
The data extracted from the WHO burden database were used to compute the ratio of the proportion of DALYs, YLDs and YLLs for MSK diseases to total DALYs, YLDs and YLLs, respectively, for each of the 183 countries. We then computed the median and 25–75th centiles interquartile range (IQR 25–75) proportion of DALYs, YLDs and YLLs, respectively, for all countries and five continents. For the years 2000, 2005, 2010 and 2015, we ranked the proportion of DALYs, YLLs and YLDs for each category of conditions for each country and each continent. To analyse temporal trends in the absolute number and proportions of DALYs, YLLs and YLDs between 2000 and 2015, we built mixed models using MSK DALYs, YLLs or YLDs (or their proportions) as the dependent variable, taking the years and the continents as the independent variables. The interaction between year and continent was tested and kept in the model if significant. Spearman's test was used to study the correlation between the proportion of MSK DALYs for each country and the GDP per capita of those countries. All statistical tests were two-sided with an α risk set at 0.05. Statistical analyses were performed using SAS 9.4 (Cary, North Carolina, USA).
Results
DALYs, YLDs and YLLs for musculoskeletal diseases (world wide)
The total number of DALYs attributed to MSK diseases worldwide increased from 80,225,634.6 in 2000107,885,832.6 to DALYs in 2015 (p<0.001). The detailed proportions of DALYs, YLLs and YLDs for MSK diseases for the years 2000, 2005, 2010, 2015 are shown in table 1.
Median proportions of DALYs, YLDs, and YLLs due to MSK diseases more than all other causes in the world for the years 2000, 2005, 2010, 2015
Among the 23 main categories of conditions reported by the WHO (see 'Methods'), MSK DALYs were ranked 10th in 2000 and ninth in 2005, 2010 and 2015 (table 2), with the median proportion of MSK DALYs increasing significantly from 3.3 (1.3–4.7) in 2000 to 4.3 (2.0–6.0) in 2015, p<0.0001. The first cause of DALYs in the world changed from infectious diseases in 2000 (601 421 046 DALYs), 2005 (534,695,389 DALYs) and 2010 (420 621 169 DALYs) to cardiovascular diseases in 2015 (407 636 500 DALYs).
Ranking of the 23 categories of DALYs in the world for the years 2000, 2005, 2010 and 2015 (by decreasing proportion over all causes)
MSK diseases remained the second cause of YLDs behind 'mental and substance use disorders' (table 3) from the years 2000 to 2015, but the total number of YLDs attributed to MSK diseases worldwide increased significantly from 77,377,709.4 to 103,817,908.4 (p=0.0008) during the same period. Between 2000 and 2015, the YLLs due to MSK diseases increased from 2,847,925.24,067,924.2 to (p=0.03) but remained ranked as the 19th disease category out of 23.
Ranking of the 23 categories of DALYs, YLLs and YLDs according to the WHO in the world, for the year 2015 (by decreasing proportion)
DALYs, YLDs and YLLs for MSK diseases (by country)
Detailed data for DALYs, YLDs, and YLLs by country are shown in table 4 and online supplementary appendix 1. In 2015, the country with the highest proportion of DALYs due to MSK diseases was Australia, with 9.8% of total DALYs for the country, 19.6% of total YLDs and 0.6% of total YLLs due to MSK diseases. Conversely, the country with the lowest proportion of MSK DALYs in 2015 was Somalia, with 0.6% of total DALYs, 5.2% of YLLs and 0% of YLDs due to MSK diseases. We observed a significant correlation (r=0.85, p<0.0001) between the proportion of MSK DALYs and countries' GDP per capita for the year 2015 (figure 1).
Supplemental material
World ranking of countries according to MSK DALYs, for the years 2000 and 2015 (by decreasing proportion)
Association between gross domestic product (GDP) per capita and proportion of disability-adjusted life years (DALYs) due to musculoskeletal (MSK) diseases. AO, Angola; AT, Austria; BN, Brunei Darussalam; BS: Bahamas; CH, Switzerland; CR, Costa Rica; DK, Denmark; GQ, equatorial Guinea; GR, Greece; IE, Ireland; IL, Israel; IR, Iran; IS, Iceland; IT, Italy; JP, Japan; KR, Republic of Korea; KZ, Kazakhstan; MT, Malta; NL, Netherlands; NO, Norway; NZ, New Zealand; PT, Portugal; QA, Qatar; SA, Saudi Arabia; SC, Seychelles; SE, Sweden; TR, Turkey; TT, Trinidad and Tobago; UAE. United Arab Emirates; UK, United Kingdom; USA, United States of America.
DALYs, YLDs and YLLs for MSK diseases (by continent)
Median proportions of DALYs, YLDs and YLLs for MSK diseases by continent are shown in table 5. In 2015, the median proportion of DALYs attributed to MSK diseases was 6.66% (IQR: 5.30–7.88) in Europe, a significantly higher figure than in all other continents, with 4.66% (3.98–5.59) in the Americas (p<0.0001 vs Europe), 4.17% (3.14–6.25) in Asia (p<0.0001), 4.14% (2.65–5.57) in Oceania (p=0.0008) and 1.33% (1.03–1.92) in Africa (p<0.0001). Interaction with time was significant for the proportions of DALYs, YLDs and YLLs, indicating an increase in the difference between countries across those years.
Median (IQR 25–75) percentage of total DALYs, YLDs and YLLs for MSK diseases, by continent
Discussion
In this study, we analysed the burden due to MSK diseases using WHO data available for the years 2000, 2005, 2010 and 2015. Our main findings are a significant increase of both the total number and proportion of DALYs due to MSK diseases over the past 15 years, with Europe being the continent where MSK diseases have the highest impact, compared with all other categories of DALYs. We further confirmed that the burden of MSK diseases is essentially due to disability (YLDs) rather than to premature death (YLLs). Finally, we observed a strong correlation between MSK disease burden and GDP per capita, suggesting an increased burden of MSK diseases in high-income countries.
The overall burden of MSK diseases, as assessed using the proportion of MSK DALYs, has been increasing significantly between 2000 and 2015 (p<0.0001), essentially owing to a significant increase in the proportion of MSK-related YLDs (p=0.0008). Importantly, in 2015 MSK diseases were the second cause of YLDs (>13% of total YLDs) in the world, after psychiatric disorders, whereas they remained the 19th cause of YLLs out of 23. This further confirms the overall low fatality of MSK diseases, with the largest proportion of MSK DALYs being due to YLDs.
Considering aggregated worldwide data, the first cause of DALYs changed from infectious diseases in 2010 to cardiovascular diseases in 2015. This may be explained by the generally better prognosis of infectious diseases and the increase in average life expectancy, especially in developing countries.16 The burden of MSK diseases as assessed using DALYs is approximately one-third of that of cardiovascular diseases, which was the first cause of DALYs worldwide in 2015.
Importantly, Europe is the continent with the highest proportion of MSK DALYs and YLDs: 6.66% (5.30–7.88) and 17.6% (16.9–18.75), respectively. In 2015, the median proportions of DALYs and YLDs due to MSK diseases in Europe were respectively five times and twice higher than those of Africa (table 5). Europe is also the continent with the highest proportion of MSK YLDs. Approximately one-fifth of Europe YLDs are due to MSK diseases (17.6% [16.9–18.75]) while at the same time YLLs remain much lower (0.3% [0.1–0.45]). Infectious diseases are still the leading causes of YLLs in Africa, with infectious diseases and respiratory infections being respectively the first and third causes of DALYs in 2015, when in Europe an epidemiological transition was observed.16 Better understanding and treatment of infectious diseases reduced their burden, and a move to diseases with higher disability, like MSK diseases, was seen.16 Conversely, infectious diseases were the 14th cause of DALYs in Europe in 2015 when cardiovascular diseases, malignant neoplasms and mental disorders were the three main causes of disease burden. However, non-communicable diseases such as cardiovascular diseases are rapidly increasing in low-income countries owing to a high natality rate and a rapid shift in lifestyle.17 Owing to this transition, MSK diseases could soon be expected to have a higher impact in those countries. Yet, the proportion of MSK YLDs remains high in Africa in 2015 (median proportion of 8.35%), showing that MSK diseases are still strongly incapacitating in this region of the world.
Correlation of MSK DALYs with countries' GDP per capita disclosed a strong impact of socioeconomic background on the burden of MSK diseases (figure 1). In 2015, the 10 countries with the highest proportion of MSK DALYs all have a GDP per capita over $20 000 per inhabitant. Conversely, the 10 countries with the lowest proportion of MSK DALYs in 2000 and 2015 are in sub-Saharan Africa. Higher-income countries often have more efficient national health systems but other key factors could account for this difference between high- and low-income countries. First, life expectancy is higher in high-income countries than in low-income countries.18 The increased disability due to MSK diseases might therefore be a reflection of the ageing of the population.9 18 Furthermore, the ratio of older to younger people is expected to increase, especially in low-income countries18 in which life expectancy is quickly increasing. Thus, the MSK burden is expected to continue to grow. Another potential explanation is the role of the widely observed epidemiological transition. Owing to the overall improvement of medical care, the prognosis of several diseases with initially high mortality has improved, hence a relative increase in disability-inducing diseases, such as mental disorders and MSK diseases. This transition is not completed at the same rate in all countries,19 which may explain the observed differences.
One important limitation of this study is the potential reporting bias, with a variable uncertainty range on available data, depending on the reporting country.15 Also, the burden of MSK diseases, as reported in this study, may vary with evolution of the methods used by WHO to calculate MSK DALYs, YLDs and YLLs.15 Finally, the grouping by continent may not fully reflect the economic heterogeneity within the continents.
Conclusion
The worldwide burden of MSK diseases, as quantified using DALYs, has significantly increased between 2000 and 2015. MSK diseases are the ninth cause of DALYs, second cause of YLDs and 19th cause of YLLs over the world. The increasing burden of MSK diseases mostly affects Europe, partly owing to ageing of the population and the global epidemiological transition observed worldwide.18 We confirmed that the overall burden of MSK disease is essentially due to YLDs rather than YLLs, suggesting a high disability but low lethality of MSK diseases. We observed a strongly significant association between MSK DALYs and the GDP per capita, underlining the role of socioeconomic background as a strong determinant of the MSK disease burden. These results are crucial to rheumatologists, and to policy makers and national healthcare systems to implement future adjustments to health plans.
Acknowledgments
The authors which to acknowledge the valuable contribution of Ms Sylvie Thuong in the handling of the manuscript.
References
Footnotes
Handling editor Josef S Smolen
Contributors LA and ES designed the study. ES, RF, FS, JS, HD, LA analyzed the data. LA, ES and HD performed the statistical analyses. LA and ES drafted the initial manuscript. All authors reviewed the drafted manuscript for critical content. All authors approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The data used for the analyses are publicly available.
Author note This study is based on publicly available data and solely reflects the opinion of its authors and not that of the World Health Organization.