Introduction: We recently demonstrated that pelvic incidence (PI) decreases after long fusion using iliac screws (ISs) and plays a role in good sagittal balance postoperatively. By contrast, the IS loosening rate may cause reversion, increasing the PI and causing loss of sagittal balance. The aim of this study was to determine the effect of the number of ISs inserted into the iliac bone for long fusion to correct adult spinal deformities (ASDs) on the frequency of IS loosening, postoperative PI, and surgical outcomes.
Methods: We included data from 70 consecutive patients. Cases in which two ISs were inserted bilaterally comprised the dual IS group (Group D), whereas cases in which one IS was inserted bilaterally comprised the single IS group (Group S).
Results: IS loosening was observed in four patients in Group D (9%) and 14 patients in Group S (61%). Both early and one-year postoperative PI were significantly smaller in Group D (P < 0.001). The sagittal vertical axis (SVA) one-year postoperatively was significantly smaller in Group D (P = 0.003).
Conclusions: The loosening rate of dual ISs was as low as about one-seventh that of single ISs. Using dual ISs, postoperative PI can be kept small, possibly resulting in a smaller SVA.
Keywords: adult spinal deformity; dual iliac screws; iliac screws loosening; pelvic anchor; sacroiliac joint; sagittal balance; spinopelvic parameter.