The reoperation rate by 3-year follow-up. From 2005 to 2008, patients using bone morphogenetic protein (BMP) had a lower reoperation rate in each year compared with patients not using BMP (1.29 and 2.21%, respectively, in 2005, p < 0.0001; 1.70 and 2.55%, respectively, in 2006, p < 0.0001; 1.63 and 3.03%, respectively, in 2007, p < 0.0001; 2.72 and 3.76%, respectively, in 2008, p < 0.001).