P92. Compared to multi rod (≥3) constructs, interbody fusion does not reduce the rate of rod failure at 2-year minimum follow-up

BACKGROUND CONTEXT Pseudarthrosis with distal mechanical failure is a common complication after long constructs in adult spinal deformity (ASD). Multiple strategies have been proposed to improve fusion rates and reduce the rate of rod fracture, including the use of interbody fusion (IBF) and multi-rod (≥3) techniques. Whether rod fracture rates are lower with the utilization of IBF versus multi-rod constructs remains unknown. PURPOSE To assess for any difference in rod fracture rate between constructs with IBF and multiple rods up to 2 years postoperatively. STUDY DESIGN/SETTING Retrospective Cohort. PATIENT SAMPLE ASD patients undergoing fusion of ≥6 levels to ilium and a minimum follow-up of 24 months. OUTCOME MEASURES Rate of postoperative rod fracture. METHODS ASD patients undergoing fusion of ≥6 levels to ilium and a minimum follow-up of 24 months were included. Patients with a history of prior fusion to L4 or below, and those with neuromuscular disease, inflammatory arthritis, or skeletal dysplasia were excluded. Patients were grouped by construct types: 2 rods w/ IBF (IBF) and w/o IBF (2R) and ≥3 rods w/o IBF (3R). Demographics, perioperative and radiographic data, and evidence of rod fracture were collected. ANOVA, chi-square and Fisher exact tests were used to compare across construct types. RESULTS Seventy-one patients were included, with mean age 65.0 years (±8.5) and BMI 26.7 kg/m2 (±5.4). In total, 20 patients had 2R constructs, 12 had IBF, and 39 had 3R. There were no significant differences in sagittal or coronal parameters at baseline or 2 years, or in OR time, EBL, or number of levels fused across groups. There were 76.1% of patients with posterior column osteotomy (2R 75.0%, IBF 50.0%, 3R 84.6%; p=0.063) and 9.9% had 3 column osteotomy. There were 12 total rod fractures (15.2%) with no significant difference between groups (2R 25.0%, IBF 16.7%, 3R 12.8%; p=0.423) and no differences in revision rate for rod fracture. CONCLUSIONS Compared to multi-rod techniques, the addition of IBF does not reduce the rate of rod fracture at two years after long constructs for ASD. These findings suggest that increasing the rigidity of the construct with the addition of a third rod may be sufficient to prevent rod fractures while IBF may provide no additional benefit at 2 years follow-up. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.