Discussion

In 2019, the global number of OA cases was approximately 527.8 million, and the number of OA patients in China reached about 100 million. Moreover, the disease burden of OA in China is still on the rise. Based on the GBD 2021 database, this study systematically analyzed the OA disease burden in China from 1990 to 2021 and projected its trend over the next 20 years. The results showed that the standardized DALY rate of OA in China was lower than the global level from 1990 to 2021; the incidence rate was lower than the global level from 1990 to 2003 but higher than the global level from 2003 to 2021. This upward shift after 2003 can be partially explained by population aging, rising national obesity prevalence and improved clinical diagnostic capacity; meanwhile, gradual healthcare system reform and enhanced outpatient medical access in China facilitated more OA case identification. Additionally, the OA disease burden in China showed an overall upward trend from 1990 to 2021, with the fastest growth in the first decade of the 21st century. The disease burden was significantly higher in females than in males, and the main affected joints were the knees and hands. Furthermore, projections indicate that the standardized incidence rate and DALY rate of OA in China will continue to rise steadily over the next 20 years, suggesting that OA control and management in China will face significant challenges in the coming decades.

The incidence rate and DALY rate of OA in China are significantly higher in females than in males, primarily due to physiological differences between genders. For example, estrogen may benefit the maintenance and health of cartilage and skeletal muscle through multiple pathways such as transforming growth factor β and insulin-like growth factor. After menopause, women's estrogen levels gradually decrease, affecting calcium absorption and utilization, thereby accelerating the degradation and wear of joint cartilage and increasing the risk of OA. In addition, low estrogen levels can induce inflammatory stressors, creating an inflammatory environment in the joints that leads to cartilage degradation and osteocyte apoptosis. On the other hand, weight gain during menarche, menopause, and pregnancy may contribute to a low-grade systemic inflammatory environment, which is another important risk factor for OA. The incidence rate of OA increases with age, and women generally have a longer life expectancy than men, resulting in a higher proportion of women in the elderly population—this may also explain the higher disease burden of OA in females. Apart from estrogen fluctuation and longer female life expectancy, divergent daily labor roles, varied occupational exposure and disparities in medical seeking behavior also contribute to gender-based OA disparity. However, the increase in OA disease burden is more pronounced in males than in females. This may be because Chinese males, as the main labor force of families and society, face higher joint loads in certain occupations such as heavy physical labor. Regardless of gender, the OA disease burden in China is still rising, and the situation is severe. Therefore, it is necessary to strengthen the popularization of OA-related knowledge, raise public awareness and attention to OA, advocate a healthy lifestyle (e.g., moderate exercise, avoiding prolonged poor posture), and encourage postmenopausal women to supplement calcium and vitamin D to maintain bone health.

OA incidence peaks at 55–59 years while DALY concentrates in people aged ≥85 years, with population aging as a core contributor [16]. In 2017, over 40% of China's population exceeded age 50 [17]; slow demographic growth under updated fertility policies [18] plus extended elderly life expectancy [19] will further expand the high-risk aging population. Shortage of specialized OA practitioners restricts standardized patient management [20], highlighting demands for policy optimization, routine elderly physical examinations and targeted health promotion.

Knee OA dominates disease burden due to lifelong high mechanical load and degenerative wear, followed by hand OA stemming from frequent daily joint use [21,22]. Contrary to global epidemiology, the strikingly low documented hip OA burden in China may be associated with insufficient screening and underdiagnosis, but this is merely an unvalidated hypothesis lacking clinical registry and imaging prevalence evidence rather than a definitive inference of true prevalence. In addition, inherent restrictions of the GBD database also restrict further refined stratified analysis for individual OA anatomical subtypes including knee OA. With no curative therapy available for OA, prevention should target verified high-risk cohorts: middle-aged women and knee OA susceptible populations, prioritizing modification of modifiable risks including obesity and acute joint injury with corresponding policy support.

As the GBD 2023 database has been newly updated, published global aggregate OA figures from GBD2023 show consistent upward secular trend of global OA burden compared with GBD2021, which indirectly supports our rising trend conclusion of China's OA burden based on GBD2021; detailed China-specific stratified 2023 OA data cannot be obtained at present, and incorporation of full GBD2023 Chinese sub-data will be prioritized in our follow-up continuous research.