Long term outcome following knee replacement in patients with juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is a disabling and destructive condition that commonly affects the knee during childhood. Our study aimed to look at the outcome of knee replacement in this uncommon group, set a benchmark for survival and determine predictors of functional results. Patients were identified from a regional specialist rheumatology clinic set up for the care of adult patients with JIA. Outcome was assessed using Stanford HAQ 20-item disability scale, patient administered WOMAC questionnaire and Knee society score. This retrospective cohort includes 34 knee replacements in 20 patients with JIA performed at a median age of 35 years with median follow up of 16 years. Median WOMAC and Knee society score at last follow up were 61.7 and 60.8 respectively. The pain component of the scores was significantly (p<0.001) better than functional component. Strong negative correlation (R=-0.79, p<0.001) was noted between Knee society function score and HAQ score. Moderate negative correlation (R=-0.42; p=0.02) was noted between Knee society function score and age at onset of the disease. Multiple stepwise regression analysis to estimate the predictors of functional results showed that the only significant (p<0.001) predictor for functional outcome was disease activity, as predicted by the HAQ score. Kaplan Meier survival analysis revealed an estimated survival of 58.5% at 20 years. Knee replacement is a satisfactory pain relieving procedure in JIA patients, although survival may be poor. Disease activity as determined by HAQ score, may predict functional results.