INTRODUCTION: Pedicle subtraction osteotomy (PSO) is being utilized with increasing frequency for correction of sagittal balance especially in patients who suffer from a flat back deformity secondary to prior surgery with interbody fusion. The goal of this report is to comment on the influence of interbody fusion on the rate of rod fracture after a PSO.
METHODS: A review of 40 patients who underwent pedicle subtraction osteotomy between 2006 and 2010 at our institution was conducted.
RESULTS: 16 patients had no prior interbody fusion and 24 had a prior interbody fusion: 18 below, 3 above and 3 both above and below the level the PSO. A total of 9 patients suffered rod fractures with the most significant difference in fracture rate between the group who never had interbody fusion (6 patients with no rod fractures) and those with a prior interbody fusion below the level of the PSO without subsequent interbody fusion above the level of the PSO (8 patients and 4 had a rod fracture). Chi square analyses demonstrated statistical significance to a P‐value<0.05. Total of 18 patients had prior interbody fusion below the level of the PSO. Of these 10 patients had subsequent interbody fusion above the level of the PSO at the time of the PSO (1 patient had rod a fracture) and 8 never had interbody fusion above the PSO (4 patients had rod fractures). A chi square analyses demonstrated a 0.05<P‐VALUE<0.1
DISCUSSION: In our series patients with prior interbody fusion below the PSO had a statistically significant higher rate of early fatigue rod fracture. We speculate that prior fusion increases the construct stiffness below the PSO placing more stress on the rod and the unfused disk above the PSO. In patients who have previously had interbody fusion below the level of the PSO, although not statistically significant, our data points to interbody fusion above the level of the osteotomy reducing the rate of early fatigue rod fractures.