Revision Total Knee Arthroplasty due to Rheumatoid Arthritis after Unicompartmental Knee Arthroplasty: A Case Report

Objective: We report a rare case of revision total knee arthroplasty (TKA) for monoarthritis of the knee due to rheumatoid arthritis (RA). The patient underwent revision surgery at 8 years and 7 months after left unicompartmental knee arthroplasty (UKA). Case: The patient was a 72-year-old woman. She subsequently presented to the previous hospital with left knee pain of spontaneous onset at 7 years and 9 months after UKA. After 8 months of conservative treatment at that hospital, she was referred to our department for surgery due to exacerbation of left knee pain and swelling. Bacteriological examination of the synovial fluid was negative, and no crystals were found by microscopic examination. When the Knee Society score was determined, the knee score was 43 points and the function score was 45 points. No periprosthetic radiolucent lines were observed and there was no loosening. Erosion of the lateral femoral and tibial condyles was observed. Based on these laboratory data obtained at the initial examination, RA was suspected. However, the patient had monoarthritis, and her score according to the 2010 American College of Rheumatology (ACR) / European League Against Rheumatism (EULAR) classification criteria for RA was only 5 points. RA was diagnosed by histopathological examination of the synovium. Detailed investigation with bone scintigraphy and gallium scintigraphy did not identify inflammation of any other joints. Discussion: Revision TKA is likely to increase in the future because of more patients undergoing UKA and an increase in the age of onset of RA. If knee pain occurs in patients after UKA, monoarthritis due to RA should be considered as a possibility. Accordingly, we should follow patients after UKA while keeping the possibility of RA in mind.