Rheumatoid arthritis (RA) and Osteoarthritis (OA) exhibited a heavy disease burden  globally. However, a systematic comparison between RA and OA is currently lacking,  encompassing their spatiotemporal trends, demographic patterns, and socio-demographic  correlates.

This study extracted incidence, prevalence, Years Lived with Disability (YLDs), and  Years of Life Lost (YLLs), with age-standardized rates (ASRs) from Global Burden of Diseases  Study 2021. Inequality index, Socio-demographic Index (SDI) correlation, decomposition, and  frontier analyses assessed the disparities and determinants of burden increase, and  Autoregressive Integrated Moving Average model projected burdens till 2040.

Global incidence and YLDs with their ASRs in RA and OA rose from 1990 to 2021,  with significant disparities in specific age distribution, female and higher SDI regions. Cross country relative inequalities narrowed over time, while absolute inequalities showed different  trends between RA and OA. Frontier analysis identified underperforming countries, such as  Mexico both in RA and OA. Decomposition analysis revealed aging and population growth  were principal factors of growing burden globally, with variations in different countries.  Globally, the ASRs of YLDs were projected to increase in RA but decrease in OA to 2040.

We report five key commonalities of RA and OA: (1)  The increasing incidence and YLDs with their ASRs indicate a growing disease burden from  1990 to 2021; (2) Females exhibit a higher disease burden compared to males in almost all age groups globally; (3) The higher the SDI, the greater the disease burden in terms of age-standardized YLDs, YLLs, and incidence; (4) In ASR of YLDs, the efficiency differences grow  as SDI increases, implying tailored improvement strategies are required for different SDI  countries; (5) Aging and population growth are responsible for the majority of the burden  increase. Critical differences between RA and OA are as follows: (1) OA mainly affects elderly  populations, while RA patients have a wider age spectrum globally; (2) Absolute inequalities  of ASR of YLDs decrease in OA but increase in RA; (3) By 2040, the global ASR of YLDs is  projected to decrease in OA but increase in RA.

The non-fatal disease burden of RA and OA increased globally from 1990 to 2021  with remarkable inequalities across sex, age, geography, and socioeconomic level. Targeted  policies and efficient management should be implemented for specific patient populations in  RA and OA.