OBJECTIVES: To evaluate the prevalence of ultrasound (US)-detected knee synovitis in patients with rheumatoid arthritis (RA) with a history of total knee arthroplasty (TKA) and to explore its association with RA disease activity and clinical outcomes. METHODS: The present, retrospective, cross-sectional study retrieved the data from electronic medical records of patients with RA who were followed up for TKA and had musculoskeletal ultrasound assessment at the study centre from 1 January 2021 through 31 December 2021. RESULTS: Forty-two patients with 67 post-TKA knee joints were enrolled in the present study. US-detected synovitis of the post-TKA knee was present in 15 knees (22.4%) and 12 patients (28.6%). There was no difference in disease activity scores or the pain domain of Knee Injury and Osteoarthritis Outcome Score between the patients with (n = 12) and without (n = 30) US-detected knee synovitis. The proportion of patients with the intensification of antirheumatic drugs after MSUS assessment was significantly higher in patients with US-detected synovitis compared to those without US-detected synovitis (41.7 versus 6.7%, P = .01). CONCLUSIONS: US-detected synovitis of the knee was present at 22.4% of post-TKA knee joints. Patients with US-detected synovitis of post-TKA knees were likely to receive an intensification of antirheumatic drugs.