Development of incident OA in cases was defined as development of frequent knee pain and radiographic OA (KL ≥1 or 2) in the same knee or in bilateral knees. Controls were individuals whose baseline Kellgren-Lawrence (KL)=0 or 1 did not change at follow-up AND who did not develop frequent pain in either knee at 24, 36, 48, 72 and 96 months. Cases and controls were matched for age, sex and BMI. Estimates of OR with 95% CIs between severity of knee OA defined as KL 1/2 versus KL 3/4 for haplotype rs419598, rs315952 and rs9005 ‘T-T-G’ are shown. Haplotypes TTG-0 or TTG-1 or TTG-2, respectively, represent carriers of 0 or 1 or 2 copies of IL1RN haplotype produced using 3 IL1RN SNPs (rs419598, rs315952 and rs9005). Data for age and BMI are presented as mean±SD; data for sex are presented as N of male and female. The ORs of patients falling into case or control groups versus IL1RN haplotype were calculated using Fisher’s exact test. Beta coefficient (and 95% CI) from logistic regressions were adjusted for ASB.

ASB, age, sex and BMI; BMI, body mass index.