Background/Purpose : To analyze the temporal trend of incidence rate (IR) of hip and/or knee total joint replacement in a cohort of rheumatoid arthritis (RA) patients

Methods : We performed a retrospective longitudinal study, including patients diagnosed of RA between 1994 and 2009, according to the 1986 ACR diagnostic criteria, attending the rheumatology outpatient clinic of the Hospital Clínico San Carlos (Madrid, Spain). Clinical records were reviewed in order to collect demographic and clinical information. Our main outcome was total hip or knee replacement surgery, considering only the first replacement per joint (multiple event variable). In order to ensure a similar maximum follow-up time for all included patients, regardless the moment when they were included, time of observation comprised only the first 5 year after RA diagnosis (from such date until both knees and hips were replaced, lost of follow-up or 5 years had elapsed). Total joint replacement (TJR) IR was expressed per 1000 patients-year. Kaplan Meier curves were set to account for all TJRs. Cox bivariate and multivariate regression models were constructed to assess the effect of calendar time, demographic and clinical-related variables in the IR. Three time intervals were considered, defined by the year of RA diagnosis: 1994-1999, 200-2004, and 2005-2009. Statistical analyses were performed using STATA v12.

Results : We included 1812 patients, 74% women, with a median (interquartile range) age at RA diagnosis of 60.4 (47.6-71.8) years, 85% Spaniards, 65% with rheumatoid factor (FR), and 48% with anti-citrullinated peptides antibodies (ACPA). 526 patients had been diagnosed between 1994-1999, 551 between 2000-2004 and 735 between 2005-2009. 69 total joints (25 hips and 44 knees) were replaced during a follow-up time of 7522.0 patients-years, resulting in an IR of 9.2 [7.2 to 11.6] per 1000 patients-year. We observed an incidence rate for the time periods 1994-99, 2000-04, and 2005-09 of 10.8 [7.3 to 16.2], 10.5 [7.4 to 15.7], and 6.9 [4.5 to 10.6], respectively (Figure 1). In the bivariate analysis, only age at RA diagnosis showed a significant association with a higher risk of TJR (p=1.0×10^-4). In the multivariate analysis (adjusted by sex, age at RA diagnosis, country of birth, presence of ACPA and FR), year of RA diagnosis was not associated with the rate of TJR (2000-2004 vs. 1994-1999: HR 0.97 [95%CI: 0.55 to 1.71], p=0.91; 2005-2009 vs. 1994-1999: HR 0.67 [95%CI: 0.37 to 1.21], p=0.18).

Conclusion : Although we observed that patient diagnosed with RA more recently had a smaller rate of TJR in our RA cohort, differences were not statistically significant. Table 1: Baseline demographic and clinical characteristics of the RA patients included in this study.

ACPA: Anti Citrullinated peptide antibodies, IQR: Interquartile range, RA: Rheumatoid arthritis.