Impact of Distal Fusion Level on Sacroiliac Joint Degenerative Change Following Adolescent Idiopathic Scoliosis Surgery

Abstract

Purpose: To evaluate the relationship between distal fusion level in correction and fusion surgery for adolescent idiopathic scoliosis (AIS) and radiologic changes in the sacroiliac (SI) joint.

Materials and methods: This retrospective cohort study evaluated patients who underwent correction and fusion for AIS between 2005 and 2017 with at least 5 years of follow-up. We categorized patients into two groups: Group 1 (distal fusion above L2, 74 patients) and Group 2 (distal fusion at L3 and below, 52 patients). Radiologic parameters and SI joint changes were evaluated on plain radiographs obtained from preoperative to 5 years postoperatively. We also investigated other risk factors for SI joint change.

Results: Analysis of demographic factors revealed no significant difference between the two groups. There was a significant difference in the incidence of SI joint change between Group 1 (5 patients, 6.75%) and Group 2 (18 patients, 34.61%), with Group 2 showing a faster increase in incidence according to the Kaplan-Meier method (p<0.0001). Preoperative lumbar lordosis (LL) and ΔLL had a significant relationship with SI joint changes [preoperative LL, hazard ratio (HR)=0.77, 95% confidence interval (CI)=0.64-0.93, p=0.008; ΔLL, HR=0.79, 95% CI=0.67-0.95, p=0.01).

Conclusion: After AIS surgery, patients who had fusion to the lower lumbar vertebrae (L3 or L4) experienced a higher incidence and faster progression of degenerative changes in the SI joint. Low preoperative LL and inadequate correction of LL during the operation were also risk factors for SI joint degeneration.

Keywords: Adolescent idiopathic scoliosis; distal fusion level; postoperative pain; sacroiliac joint.

Fig. 1. Flowchart of the study. AIS, adolescent idiopathic scoliosis; SI, sacroiliac.

Fig. 2. Plain radiographs of sacroiliac joint changes defined in this study. (A) Normal. (B) Sclerosis. (C) Erosion. (D) Joint space narrowing.

Fig. 3. Cumulative incidence of sacroiliac (SI) joint changes after fusion procedures for adolescent idiopathic scoliosis. The changes in the SI joint were more rapid and the number of patients who underwent SI joint change was greater in Group 2 (p<0.0001).

Fig. 4. Multi-factor analysis of SI joint change using Cox proportional hazards regression. The distal fusion level, preoperative lumbar lordosis (LL), and LL change during operation showed statistical relationship [distal fusion level, hazard ratio (HR)=22.58, p<0.001; preoperative LL, HR=0.77, p=0.008; LL change, HR=0.79, p=0.01].