E062 Calcium pyrophosphate dihydrate crystal in operated rheumatoid arthritis of the knee

Background/Aims Calcium pyrophosphate dihydrate (CPPD) crystals are also one of the common types of crystals causing crystal-induced inflammatory arthritis. Several studies have elucidated important aspects of the molecular and cellular mechanisms of CPPD crystal formation. CPPD crystal deposition disease is a common arthritic disorder in mainly elderly patients. CPPD crystals are found in multiple joints (e.g. knee, wrist joints) in association with severe cartilage degeneration in osteoarthritis. However, there are few reports concerning about CPPD crystals in patients with rheumatoid arthritis (RA). In this study, I investigated the relationship between CPPD crystal and operated RA of the knee. Methods Seventy-seven total knee arthroplasties were performed for RA knees from January 2016 to September 2021. I defined the lower extremity alignment (LEA) base on the femorotibial angle (FTA) as valgus (FTA Results CPPD crystals were detected from 19 RA knees (27.1%). There were no significant differences between CPPD(+) and (-) groups about age, gender, FTA, BMI, CRP, ESR and MMP-3. The more severe osteophyte formation showed higher CPPD(+) rate tendency; however, there was no significance. CPPD(+) rates were 34.2% in varus knees, 23.1% in valgus knees and 18.2% in neutral knees, respectively. We reported that age, valgus knee, severe osteophyte and low BMI were the risk factors of CPPD(+) in operated osteoarthritis (OA) knees, previously. In this study, there was no difference between CPPD(+) and (-) groups about these factors. Especially, CPPD(+) rate in RA valgus knees was one third of that of OA valgus knees. Conclusion It may be suggested that CPPD production mechanism in RA knees is different from that in OA knees. Disclosure M. Nishikawa: None.