Rate of cartilage loss at two years predicts subsequent total knee arthroplasty: a prospective study.

OBJECTIVE To determine whether cartilage volume loss is an independent predictor of knee replacement. DESIGN Prospective community based, four year prospective cohort study. METHODS 123 subjects with mild to moderate symptomatic radiographic knee osteoarthritis were recruited by either advertising, the Victorian branch of the Arthritis Foundation of Australia, treating general practitioners, orthopaedic surgeons, or rheumatologists; 113 completed the study. Magnetic resonance imaging was carried out at baseline and at 2 years on the symptomatic knee. Rate of change in tibial cartilage volume was calculated. Subjects were then followed up at year 4 to determine whether they had undergone a knee replacement. RESULTS The rate of tibial cartilage loss over two years was an independent predictor of knee replacement at four years. For every 1% increase in the rate of tibial cartilage loss there was a 20% increase risk of undergoing a knee replacement at four years (95% confidence interval, 10% to 30%). Those in the highest tertile of tibial cartilage loss had 7.1 (1.4 to 36.5) higher odds of undergoing a knee replacement than those in the lowest tertile. WOMAC score at baseline, female sex, and tibial bone size (but not age and radiographic score) were also predictors of knee replacement. CONCLUSIONS The data suggest that treatment targeted at reducing the rate of knee cartilage loss in subjects with symptomatic osteoarthritis may delay knee replacement. This has important implications in terms of prevention and therapeutic interventions in osteoarthritis.