Rod Fracture After Pedicle Subtraction Osteotomy Using a Side-Tightening Pedicle Screw System in Consecutive Case Series

OBJECTIVE: The objective of this study was to investigate the incidence and risk factors of rod fractures (RFs) after a single-level lumbar pedicle subtraction osteotomy (PSO) using a side-tightening (ST) pedicle screw system. METHODS: Fifty-seven consecutive patients who underwent a single-level lumbar PSO for the degenerative sagittal imbalance at a single institution were retrospectively reviewed. All surgeries were performed by a single surgeon using an ST pedicle screw system. Demographic, surgical, and radiographic data were analyzed to investigate the incidence and risk factors for RF. RESULTS: Seven (12.3%) patients showed RF after PSO. Four patients had bilateral RFs, and 3 patients had unilateral RFs. The location of the RF was at the PSO level in 6 of 7 patients. The ratio of adjacent interbody fusion was significantly different between the group with RF and the group without RF (16.7% vs. 74.0%, P = 0.004). The preoperative segmental angle at the PSO vertebra (-6.1 degrees +/- 5.5 degrees vs. -1.7 degrees +/- 4.6 degrees, P = 0.049) and postsurgical change in lumbar lordosis (48.4 degrees +/- 8.8 degrees vs. 37.8 degrees +/- 11.9 degrees, P = 0.033) were significantly different between the 2 groups. Risk factor analysis using stepwise logistic regression analysis revealed that the absence of an adjacent interbody cage (odds ratio = 0.011, 95% confidence interval = 0.000-0.390, P = 0.013) was a significant risk factor. CONCLUSIONS: The incidence of RF after a single-level lumbar PSO using the ST pedicle screw system was 12.3% in our cohort. The absence of an adjacent interbody cage was a significant risk factor for RF.