Associations Between Oxidative Stress, Inflammation, Muscle Mass, and Sarcopenia Phenotypes in Older Adults with End-Stage Knee and Hip Osteoarthritis: A Cross-Sectional Study

Background: Skeletal muscle impairment is common in older adults with end-stage knee and hip osteoarthritis (OA) and contributes to disability and functional decline. Τhe relative contributions of muscle mass, muscle strength, systemic inflammation and oxidative stress to sarcopenia phenotypes in this population remain incompletely understood. This study investigated the associations between muscle-related parameters, inflammatory and oxidative stress biomarkers, and sarcopenia phenotypes in older adults with end-stage OA. Methods: This cross-sectional study included 88 older adults scheduled for primary total knee (n = 56) or total hip arthroplasty (n = 32). Body composition, muscle strength, physical performance, and biochemical markers were assessed using standardized procedures. Systemic inflammation was evaluated using C-reactive protein (CRP) and the neutrophil-to-lymphocyte ratio (NLR), whereas oxidative stress was assessed by urinary F2-isoprostanes. Sarcopenia status was categorized according to the European Working Group on Sarcopenia in Older People 2 (EWGSOP2) criteria. Results: Overall, 29.5% of participants were classified as having probable/confirmed sarcopenia phenotypes, with similar prevalence in knee and hip OA. Sarcopenic participants exhibited significantly lower appendicular skeletal muscle mass (ASMM), reduced handgrip strength, slower gait speed, poorer physical performance and higher body fat percentage than those without sarcopenia. Muscle strength demonstrated stronger associations with physical performance than muscle mass and remained an independent predictor of Short Physical Performance Battery (SPPB) score after adjustment for age, gender and muscle mass. Higher urinary F2-isoprostane concentrations were independently associated with lower ASMM after adjustment for demographic characteristics and inflammatory biomarkers, whereas CRP and NLR were not independently associated with muscle-related outcomes in the fully adjusted models. Conclusions: Nearly one-third (29.5%) of older adults with end-stage knee and hip OA were classified as having probable or confirmed sarcopenia according to the EWGSOP2 criteria. Oxidative stress was independently associated with skeletal muscle mass, whereas CRP and NLR were not independently associated with muscle-related outcomes. These findings highlight the relevance of muscle strength and oxidative stress in older adults with end-stage OA and warrant further longitudinal investigation.