Periprosthetic Joint Infections After Unicompartmental Knee Arthroplasty Occur More Commonly in Patients Who Have Rheumatoid Arthritis.

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has been historically contraindicated in those who have rheumatoid arthritis (RA). Our primary aim was to evaluate whether patients who have RA had higher rates of periprosthetic joint infection (PJI) following UKA. Our secondary aim was to evaluate whether RA patients taking disease-modifying antirheumatic drugs (DMARDs) had higher rates of PJI than RA patients not taking DMARDs.

METHODS

A national database was queried for patients who underwent primary UKA over a 20-year period. The resulting 18,518 patients were separated into those who had RA (UKA with RA) and those who did not have RA (UKA without RA). Through a process of one-to-one propensity matching, equal cohorts of 791 patients were formed. The RA cohort was divided into patients who had taken a DMARD up to six months before surgery or any time after surgery (RA with DMARD, n = 342) and those who did not (RA without DMARD, n = 477). The propensity matching process was used, resulting in 310 patients in the RA with DMARD and the RA without DMARD cohorts. Relative risk (RR) was used to compare the frequencies of PJI between each of the groups with 95% confidence intervals (CIs). Any P-values less than 0.05 were considered significant.

RESULTS

Thirteen (1.6%) patients in the UKA without RA cohort had a PJI at any point after surgery, compared with 32 (4.0%) in the UKA with RA cohort. This represents an RR of 2.5 (95% CI 1.3 to 4.7, P = 0.004). There were 20 (6.5%) patients in the RA with DMARD cohort who developed a PJI compared to ≤ 10 (3.2%) in the RA without DMARD cohort. This represents an RR of 2.0 (95% CI 1.0 to 4.2, P = 0.06).

CONCLUSIONS

Patients who had RA who underwent UKA had an increased risk of PJI compared to patients who did not have RA. There was no difference in the PJI rate in RA patients taking DMARDs compared to those who did not take DMARDs.