Biomarkers Related to Sarcopenia and Physiological Reserve in Total Joint Arthroplasty and Other Clinical Populations

Sarcopenia is increasingly recognized as a multidimensional syndrome reflecting impaired physiological reserve rather than isolated skeletal muscle loss.Although numerous circulating biomarkers have been associated with sarcopenia and adverse orthopaedic outcomes, their biological significance varies according to the underlying clinical context.This narrative review integrates current evidence on circulating biomarkers of sarcopenia and physiological reserve across elective total hip and knee arthroplasty, fragility hip fracture, community-dwelling older adults, and medically complex populations.The available evidence demonstrates that sarcopenic phenotypes differ substantially between these populations, with predominantly disuse-related muscle deterioration in elective arthroplasty, frailty-associated sarcopenia after hip fracture, and metabolically driven muscle loss in chronic systemic diseases.Nutritional (albumin, geriatric nutritional risk index), inflammatory (C-reactive protein (CRP), neutrophil-to-lymphocyte ratio, CRP-to-albumin ratio), metabolic (aspartate aminotransferase-to-alanine aminotransferase ratio, glucoseto-albumin ratio), endocrine (vitamin D, insulin-like growth factor-1), and emerging molecular biomarkers reflect complementary biological domains of physiological reserve rather than directly measuring skeletal muscle quantity or quality.Current evidence supports their greatest clinical value in perioperative risk stratification and identification of patients at increased risk of adverse postoperative outcomes, whereas the diagnosis of sarcopenia should continue to rely on established assessments of muscle strength, muscle quantity and/or quality, and physical performance.Integrating circulating biomarkers with established sarcopenia assessment may improve patient phenotyping, individualized perioperative optimization, and risk prediction, although methodological standardization and prospective multicenter validation are required before widespread clinical implementation.