Rod fracture after long construct fusion in adult spinal deformity surgery: A retrospective case-control study

Very few studies have focused on the complication of rod fracture after posterior long construct fusion in adults with spinal deformity. Therefore, this retrospective study aimed to investigate the incidence and risk factors of this complication. The study reviewed 213 adult patients with spinal deformity treated by long construct fusion between January 2009 and January 2017. Ten patients (4.6%) with rod fracture were included in the case study group. For each case of rod fracture, we selected two age-matched and gender-matched controls. Independent two-sample t test and Chi-square test were used to compare the differences between variables. Binary logistic regression analysis was performed to identify independent risk factors of rod fracture. Statistically significant differences were observed between the groups, in terms of additional bone grafts volume (P = 0.015), osteotomy (P = 0.017), skipped screw in sagittal apex region (P = 0.012), TK change (P = 0.023), and preoperative TLK (P = 0.036). However, there were no differences in terms of age (P = 0.933), follow-up time (P = 0.513), gender distribution (P = 0.650), fusion segments (P = 0.085), the number of screws (P = 0.131), density of screws (P = 0.088), preoperative MC (P = 0.120), postoperative MC (P = 0.430), MC change (P = 0.126), preoperative TK (P = 0.590), postoperative TLK (P = 0.074), TLK change (P = 0.064), preoperative LL (P = 0.084), postoperative LL (P = 0.065), and LL change (P = 0.914). Binary logistic regression analysis revealed that osteotomy (P = 0.023) and skipped screw strategy in sagittal apex region (P = 0.046) were the primary factors included in the equation [Odds Ratio (OR) = 11.669 and 7.659, respectively]. In our study, the prevalence of rod fracture in adult patients with spinal deformity after long construct fusion was 4.6%; osteotomy was the main risk factor of rod fracture these patients. The skipped screws in sagittal apex region could increase the risk of rod fracture because the stress on the rods failed to be distributed to different segments.