Seronegative rheumatoid arthritis found in an 85-year-old woman during preoperative investigations for knee replacement surgery for osteoarthritis.

This report describes the case of an 85-year-old woman who was found to have seronegative rheumatoid arthritis during preoperative investigations for knee replacement surgery for osteoarthritis. Follow-up for knee osteoarthritis was continued for many years without any symptoms involving other joints. Before total knee arthroplasty for osteoarthritis, preoperative investigations revealed a highly inflammatory state. After differential diagnosis, seronegative rheumatoid arthritis was diagnosed. Even in preoperative investigations before total knee arthroplasty for very old patients with osteoarthritis, the possibility of rheumatoid arthritis developing should always be kept in mind.