160. Survival analysis using fusion status after adult spinal deformity (ASD) surgery with minimum 4-year follow-up

Abstract

BACKGROUND CONTEXT Prior reports have focused on grading fusion status after adult spinal deformity (ASD) surgery; however, few focused on fusion status after 4-years postop. PURPOSE To identify risk factors for nonunion in a prospective cohort of ASD patients with long-term follow-up (=4 years). STUDY DESIGN/SETTING Prospective multicenter observational series. PATIENT SAMPLE Database enrollment required age =18 years, scoliosis =20°, sagittal vertical axis (SVA) =5cm, pelvic tilt =25°, or thoracic kyphosis =60°. OUTCOME MEASURES Fusions were rated as bilaterally fused (A), unilaterally fused (B), partially fused (C), or not fused (D). Primary outcome was fusion (grade A or B) vs nonunion (grade C or D) at minimum 4-year follow-up. Secondary outcome measures included health-related quality of life (HRQL) (Oswestry Disability Index [ODI], Short Form-36 [SF-36] scores, Scoliosis Research Society-22 [SRS-22r] scores). METHODS Surgically treated ASD patients prospectively enrolled into a multicenter study (2008-2020) were assessed for fusion (grade A or B) vs nonunion (grade C or D). Inclusion required postop fusion grading at minimum 4-year follow-up. Demographics, frailty, comorbidities, alignment (baseline and initial correction), index surgery (total levels fused, iliac fixation, interbody fusion [IBF], use of bone morphogenetic protein [BMP] and/or demineralized bone matrix [DBM], 3-column osteotomy [3CO]) were assessed to identify potential predictors of nonunion (grade C or D), which were then analyzed using Kaplan-Meier survival curves and log-rank comparisons. RESULTS A total of 227 patients achieved minimum 4-year follow-up and were included (age 58±14y, 82% women, BMI 27±5kg/m2, 40% prior spine surgery, ASD-FI 0.31 [frail], 15% osteoporosis). Index operations had 12±4 posterior levels, 70% iliac fixation, 62% IBF, 76% had BMP, 33% had DBM (of which 52% also had BMP), and 15% had 3CO. At final follow-up, 61 patients (27%) demonstrated nonunion (grade C or D). Older age (61±14 vs 57±14, p=0.015), no BMP usage (p 60 years) had significantly higher probability of nonunion (log-rank test p=0.024), and BMP had protective effect (log-rank test p 0.05). CONCLUSIONS This study demonstrated that older age (>60 years) was associated with significantly higher rates of nonunion at long-term follow-up (4 years) after ASD surgery, and that use of BMP had significant protective effect against this complication. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. Prior reports have focused on grading fusion status after adult spinal deformity (ASD) surgery; however, few focused on fusion status after 4-years postop. To identify risk factors for nonunion in a prospective cohort of ASD patients with long-term follow-up (=4 years). Prospective multicenter observational series. Database enrollment required age =18 years, scoliosis =20°, sagittal vertical axis (SVA) =5cm, pelvic tilt =25°, or thoracic kyphosis =60°. Fusions were rated as bilaterally fused (A), unilaterally fused (B), partially fused (C), or not fused (D). Primary outcome was fusion (grade A or B) vs nonunion (grade C or D) at minimum 4-year follow-up. Secondary outcome measures included health-related quality of life (HRQL) (Oswestry Disability Index [ODI], Short Form-36 [SF-36] scores, Scoliosis Research Society-22 [SRS-22r] scores). Surgically treated ASD patients prospectively enrolled into a multicenter study (2008-2020) were assessed for fusion (grade A or B) vs nonunion (grade C or D). Inclusion required postop fusion grading at minimum 4-year follow-up. Demographics, frailty, comorbidities, alignment (baseline and initial correction), index surgery (total levels fused, iliac fixation, interbody fusion [IBF], use of bone morphogenetic protein [BMP] and/or demineralized bone matrix [DBM], 3-column osteotomy [3CO]) were assessed to identify potential predictors of nonunion (grade C or D), which were then analyzed using Kaplan-Meier survival curves and log-rank comparisons. A total of 227 patients achieved minimum 4-year follow-up and were included (age 58±14y, 82% women, BMI 27±5kg/m2, 40% prior spine surgery, ASD-FI 0.31 [frail], 15% osteoporosis). Index operations had 12±4 posterior levels, 70% iliac fixation, 62% IBF, 76% had BMP, 33% had DBM (of which 52% also had BMP), and 15% had 3CO. At final follow-up, 61 patients (27%) demonstrated nonunion (grade C or D). Older age (61±14 vs 57±14, p=0.015), no BMP usage (p 60 years) had significantly higher probability of nonunion (log-rank test p=0.024), and BMP had protective effect (log-rank test p 0.05). This study demonstrated that older age (>60 years) was associated with significantly higher rates of nonunion at long-term follow-up (4 years) after ASD surgery, and that use of BMP had significant protective effect against this complication.