Relationship between iliac screw loosening and proximal junctional kyphosis after long thoracolumbar instrumented fusion for adult spinal deformity

Abstract

Purpose Authors assumed that the stability of iliac screw (IS) fixation could affect the development of proximal junctional kyphosis (PJK). The purpose of this study was to analyze the relationship between IS loosening and PJK after long fusion surgery for adult spinal deformity (ASD). Methods Sixty-eight ASD patients (6 males, 62 females; mean age, 68.1 years) who underwent long fusion surgery with IS fixation were reviewed. The incidence and risk factors of IS loosening were investigated. The relationship between IS loosening and PJK was also analyzed. Results IS loosening and PJK appeared in 33 and 19 patients, respectively. The median time for IS loosening and PJK to develop was 6.0 months (range 1.3–59.2) and 9.1 months (range 1.3–73.2), respectively. PJK developed in patients without IS loosening more frequently than in patients with IS loosening. PJK did not develop in 28 patients who presented with IS loosening first. IS loosening developed 5 months postoperatively in those 28 patients, whereas IS loosening was present 11 months postoperatively in 4 patients who presented with PJK first. Preoperative PT (OR = 1.091) and IS loosening (OR = 0.343) were significantly related with the development of PJK. IS loosening was significantly associated with postoperative PI-LL > 10° (OR = 0.957), postoperative SVA (OR = 1.023), and postoperative PT (OR = 1.072). Conclusion Postoperative sagittal malalignment should be avoided to prevent IS loosening and PJK. IS loosening occurred earlier than PJK and seemed to affect the development of PJK. This relationship supports the hypothesis that distal stability of long constructs may increase proximal junctional stress. Level of evidence III. Graphic abstract These slides can be retrieved under Electronic Supplementary Material.