1. Use of ALIF at the lumbosacral junction results in less lumbopelvic fixation failure than TLIF or no interbody fusion following correction of adult spinal deformity

Abstract

BACKGROUND CONTEXT Based on biomechanical studies, the use and type of interbody device at the lumbosacral junction creates variable stress/strain on the lumbopelvic fixation. This variability may lead to differential failure mechanisms and rates within following correction of adult spinal deformity (ASD). PURPOSE We aimed to evaluate the relationship of lumbosacral interbody presence and type with lumbopelvic fixation failure after ASD correction utilizing iliac (IS) or S2 alar iliac (S2AI) screws. STUDY DESIGN/SETTING Retrospective review of prospective, multicenter ASD database. PATIENT SAMPLE A total of 342 patients. OUTCOME MEASURES Pelvic fixation loosening, IS/S2AI screw fracture, S1 screw fracture, rod fracture (below L4), revision surgery, pseudarthrosis, HRQLs. METHODS Inclusion criteria consisted of patients with ASD (coronal Cobb ≥20°, sagittal vertical axis (SVA) ≥5cm, pelvic tilt ≥25° and/or thoracic kyphosis >60°) ≥18 years old and 2yr f/u who underwent >5 level fusion with pelvic fixation. Patients with prior L5-S1 fusion were excluded. Patients were divided into three groups based on the lumbosacral interbody fusion strategy (none, ALIF, TLIF/PLIF). Univariate testing via one-way ANOVA and chi-square tests, and multivariate logistic regression, accounting for significant confounders, were used to examine the difference between the three groups in regard to pseudarthosis, pelvic fixation loosening, rod fracture and revision surgery. Level of significance=p RESULTS A total of 342 patients met inclusion criteria (L5-S1 interbody groups: none=164, ALIF=87, TLIF=91). The three groups were similar in terms of baseline comorbidities, gender, BMI, pelvic fixation type (iliac screws vs S2AI), and use of BMP2 posteriorly. There were differences in rate of interbody BMP2 use (ALIF 22.9%, TLIF 48.35%, p=0.0001), use of unilateral pelvic fixation (none 7.36%, ALIF 19.8%, TLIF 3.29%, p=0.0001) and age (none 65.41, ALIF 60.47, TLIF 63.81, p=0.0005). Multivariate logistic regression revealed ALIF at L5-S1 was associated with lower odds of pseudarthrosis (OR 0.16, p-0.026) and rod fracture (OR 0.19, p=0.012) compared to no interbody fusion, while TLIF was no different than no interbody. There were no differences between groups in regard to pelvic fixation loosening or revision surgery. CONCLUSIONS The use of ALIF at L5-S1 during correction of ASD protects against fixation failure at the lumbopelvic junction compared to the use of TLIF or no interbody. This more protective effect of ALIF at the lumbosacral junction may allow for selective unilateral pelvic fixation for ASD surgery. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.