The effect of three years of TNF-α blocking therapy on BTM in patients with AS. (A) bone formation marker BALP. (B) bone formation marker PINP. (C) bone resorption marker sCTX. Z-scores were calculated to correct for the normal influence that age and gender have on bone turnover. Data were available for 100%, 92.6%, 95.4%, 97.2%, 97.2% and 90.3% of the 72 patients at 0, 3, 6, 12, 24 and 36 months, respectively. Box-and-whisker plots (Tukey): boxes indicate medians with interquartile ranges; + indicate means; whiskers indicate 1.5 times the interquartile distances; • indicate outliers. a: P < 0.001 compared to values recorded at baseline. b: P < 0.05 compared to values recorded at baseline. c: P < 0.05 and P < 0.01 compared to values recorded at 6 and 24 months, respectively. d: P < 0.05 and P < 0.01 compared to values recorded at 12 and 24 months, respectively.