Musculoskeletal (MSK) pain refers to pain, either acute or chronic, affecting muscles, bones, joints, tendons, and even nerves. Common types include low back pain, neck pain, and the pain associated with osteoarthritis. These pains are the leading cause of work disability, sick leave, presenteeism, and reduced productivity. MSK pain is the leading cause of disability in the United States in 2021, ranking first in years lived with disability and fourth in disability-adjusted life years. Moreover, MSK pain is often chronic and progressive, placing a considerable strain on healthcare systems and financial resources. Estimates of US healthcare spending in 2016 revealed that low back and neck pain had the highest costs, at $134.5 billion, followed by other MSK pain, which accounted for $129.8 billion.

As the U.S. population ages, the prevalence of MSK issues may rise, leading to increased demands on the healthcare system. Although the Bone and Joint Decade 2000-2010 raised awareness about the burden of MSK conditions, significant gaps in health system improvements persist. National health policies and strategies addressing MSK health as part of noncommunicable disease care remain inadequate relative to the burden of these condition such as cardiovascular disease. Achieving the 2030 Agenda for Sustainable Development and promoting health throughout life requires a renewed and sustained focus on improving MSK health at both national and global levels. Tracking the prevalence trends of MSK pain may offer valuable insights into critical public health issues, including shifts in disease burden, healthcare access, adoption of effective therapies, and reduction in the use of inappropriate or ineffective treatments. However, previous studies have mostly focused on low back pain, and neck pain. To date, very few studies have examined trends of site-specific MSK pain prevalence using national representative sample. Prevalence and trends in other sites are also important, but no relevant studies were found. The absence of such data poses challenges in accurately estimating the burden of MSK pain.

In addition, in disease trend analysis, temporal trends generally encompass multiple dimensions. For individuals with MSK pain, prevalence risk can be divided into age, period, and birth cohort effects. Age effects reflect the influence of an individual's chronological age on MSK pain prevalence. Period effects pertain to the influence of external factors on the whole population at a particular time. These factors may include changes in medical technology, public health policies, or social and economic conditions. Cohort effects reflect the impact of common experiences and exposures unique to a particular generation or birth cohort, regardless of period or age. Understanding the contribution of age-period-cohort effects and identifying potential moderating factors for each enhances comprehension of macro-level exposures, aiding in data-driven planning.

Furthermore, Healthy People 2010 and 2020, the U.S. national public health blueprint, targeted the elimination of health disparities, including those related to MSK pain, and the attainment of health equity. To assess progress toward this objective, it is crucial to evaluate disparities in MSK pain prevalence.

In this study, utilizing a large, nationally representative sample of the US population, our objective was to explore the prevalence trends of 11 site-specific MSK pain from 1999 to 2018. We also identified cohort patterns in MSK pain prevalence, isolating age, period and cohort effects. Furthermore, we also investigated these trends across various demographic factors such as race/ethnicity, gender, age, and socioeconomic status to determine whether health disparities persist.