Association of sarcopenia and its prognostic value in symptomatic knee osteoarthritis among older people in China: the first longitudinal evidence from CHARLS

Sarcopenia and knee osteoarthritis (KOA) are two common musculoskeletal disorders, often coexisting in aged population and potentially influencing each other. However, the underlying relationship between two conditions remains unclear and controversial. To fill this knowledge gap, we aimed to investigate the longitudinal association among the older Chinese population. Data were attracted from 2 waves of the China Health and Retirement Longitudinal Study (CHARLS), and 6212 individuals aged ≥ 60 years were included. Sarcopenia status was defined by the Asian Working Group for Sarcopenia 2019 criteria. Multivariate logistic regression and generalized estimation equation models were applied to estimate the impact of sarcopenia on KOA. A prognostic nomogram was developed through train-test cross-validation. At baseline in CHARLS 2015, the prevalence of symptomatic KOA was 12.7% (792/6212) in total population, 9% (270/2996) in no-sarcopenia group, 17.5% (286/1638) in possible sarcopenia group, and 15.0% (236/1578) in sarcopenia group. Over a 3-year follow-up, 4980 respondents were included, with incident KOA cases identified as 56 (2.2%), 38 (3.0%), and 43 (3.6%) in no-sarcopenia, possible sarcopenia, and sarcopenia groups, respectively. Sarcopenia was significantly associated with increased new-onset KOA compared to no-sarcopenia peers in the fully adjusted model (OR: 1.91, 95% CI: 1.15–3.18), whereas this association was non-significant for possible sarcopenia. In females, low muscle mass alone significantly increased the incident risk of KOA (OR: 2.58, 95% CI: 1.05–6.49). The final prognostic model and nomogram, including sarcopenia status, age, gender, body mass index, self-reported health status, comorbidities, history of falls and physical activity, had a considerable discrimination (AUC = 0.744, C-index = 0.660). The calibration curve indicated significant agreement between predicted and actual observations. Decision curve analysis revealed net benefits for clinical intervention at a probability threshold of 1–17%. Sarcopenia was associated with a higher incident risk of symptomatic KOA, wherein low muscle mass may play an important role. The inferior prognosis of sarcopenia in KOA needs more attention in clinical practice.