Sarcopenia severity and its prognostic value for structural and functional progression in elderly patients with knee osteoarthritis: a 24-month retrospective cohort study

BACKGROUND: Sarcopenia is a age-related symptom characterized by loss of muscle mass and strength, which often coexists with knee osteoarthritis (KOA). OBJECTIVE: In the current study, the association between sarcopenia severity and the progression of KOA among elderly patients was explored. METHODS: A total of 226 KOA patients aged ≥ 60 years were followed for 24 months. Sarcopenia was diagnosed into non-sarcopenia, probable, confirmed, and severe categories. Outcomes included Kellgren-Lawrence (KL) progression, joint-space width (JSW) narrowing, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) deterioration, functional decline, and biochemical changes. Multivariate logistic regression identified independent predictors. Model performance was evaluated using ROC curves, calibration plots, and decision-curve analysis (DCA). RESULTS: Radiographic progression increased stepwise with sarcopenia severity (KL progression: 25% to 65%; JSW narrowing: 30% to 68%, P < 0.001). Confirmed or severe sarcopenia independently predicted 24-month progression (OR = 2.58, 95% CI 1.33-5.01). Additional predictors included slower gait speed, lower phase angle, elevated CRP and IL-6, reduced albumin, and lower 25 (OH)D levels. The multivariable model integrating these factors achieved strong discrimination (AUC = 0.86), excellent calibration, and meaningful net clinical benefit on DCA, outperforming sarcopenia severity alone (AUC = 0.68). Kaplan-Meier curves demonstrated earlier progression in more severe sarcopenia groups. CONCLUSIONS: Sarcopenia severity is strongly associated with earlier KOA progression by interacting with biomechanical, inflammatory, and nutritional pathways. Thus, a multidimensional model incorporating functional, inflammatory, and nutritional parameters substantially improves prognostic accuracy.