Background <p>We evaluated longitudinal changes in sarcopenia status using the operational definition in patients with advanced knee osteoarthritis and limited mobility.</p> Methods <p>In this prospective cohort study, we enrolled Korean women aged ≥ 60&#xa0;years who underwent total knee arthroplasty (TKA) for primary osteoarthritis. Sarcopenia assessments based on the Asian Working Group for Sarcopenia 2019 definition and clinical outcomes were collected preoperatively and at 6 and 12&#xa0;months postoperatively. Differences by sarcopenia status and longitudinal changes were analyzed using linear mixed models (LMMs). We also examined the proportion of patients meeting diagnostic criteria for each sarcopenia item and analyzed the changes from preoperative values.</p> Results <p>Among the 146 participants (mean age 71.8 ± 6.2&#xa0;years), 106 and 79 were followed up at 6&#xa0;months and 1&#xa0;year, respectively. Preoperative physical performance was not assessed in 7 patients (4.8%, 10 knees) owing to pain. At all time points, the sarcopenic group showed lower skeletal muscle mass index (SMI) than the non-sarcopenic group, with no other differences except preoperative short physical performance battery score (<i>p</i> = 0.015). Longitudinally, TKA improved outcomes and performance, while handgrip strength declined and SMI remained stable. The proportion of participants meeting low physical performance criteria decreased postoperatively, whereas those meeting low handgrip strength increased.</p> Conclusion <p>TKA improved physical performance longitudinally, whereas muscle strength and mass did not. Grouping according to the operational definition revealed no postoperative differences in physical performance or muscle strength. The current operational definition of sarcopenia may be unsuitable for patients with severe knee osteoarthritis, as joint pain influences physical&#xa0;performance.</p> Level of evidence <p>Prospective comparative study.</p> ClinicalTrials.gov Identifier <p>NCT06136039.</p>