Rod fracture after long construct fusion for spinal deformity: clinical and radiographic risk factors

Background No reports have been published on detailed risk factors for rod fracture after spinal deformity correction and fusion. The purpose of this study was to analyze clinical and radiographic risk factors of rod fracture after long construct fusion for spinal deformity. Methods The survey subjects were 155 cases who were diagnosed with spinal deformity and underwent correction and fusion surgery with long construct instrumentation (>3 levels, average 10.3 levels) between July 2004 and June 2010. The subjects comprised 32 males and 123 females with a mean age of 19.0 (range 8-78) years. The mean Cobb angle was 61.0 +/- 16.1 degrees preoperatively and 25.7 +/- 16.9 degrees postoperatively. Univariate analysis and logistic regression analysis were performed. Results Rod fracture occurred in 8 of 155 cases (5.2 %). The mean period from surgery to rod fracture was 18.1 months (range 2-37). The level of fracture ranged from the thoracolumbar junction to the lumbosacral vertebrae. Six patients had fracture near the fused lower end and two patients had fracture at the thoracolumbar junction. Univariate analysis revealed that non-ambulatory status, preoperative kyphosis, small-diameter rods, multiple surgery, and use of iliac screws were significant risk factors for rod fracture. Sex, obesity, severity of preoperative scoliosis, and rod material were not significant risk factors. Logistic regression analysis revealed that use of iliac screws (odds ratio: 81.9, 95 % confidence interval: 7.2-935.0, p < 0.001) and small-diameter (<6 mm) rods (odds ratio: 16.3, 95 % confidence interval: 1.7-152.6, p = 0.015) were risk factors for rod fracture. Conclusions The incidence of rod fracture after long construct fusion for spinal deformity was 5.2 %. Iliac screw fixation and small-diameter rods were risk factors for rod fracture.