Mismatch between Pelvic Incidence and Lumbar Lordosis is the Key Sagittal Plane Determinant of Patient Outcome at minimum 40 Years after Instrumented Fusion for Adolescent Idiopathic Scoliosis

STUDY DESIGN Retrospective review. OBJECTIVE Assess measures of spinal-pelvic balance in predicting functional outcome in patients who underwent posterior spinal fusion for adolescent idiopathic scoliosis (AIS) at minimum 40-year follow-up. SUMMARY OF BACKGROUND DATA Back pain and long-term function are considered when choosing levels for surgery in AIS patients. Three hundred and fourteen patients underwent fusion for AIS between 1961 and 1977. One hundred and thirty-four patients were located for potential long-term follow-up. METHODS With IRB approval, medical records and public resources were used to locate patients. Patients completed health related quality of life instruments, and returned for assessment including full radiographs. Radiographs were analyzed for scoliosis measures, and recognized spinal-pelvic measures including the lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic incidence (PI) and pelvic tilt (PT). Bivariate and multivariable analyses were performed to assess the association between spinal-pelvic measures and patient-reported outcomes (PROs). RESULTS Thirty-five of 134 patients agreed to return for complete health related quality of life (HRQoL) and radiographic follow-up. There were no differences at baseline between those agreeing and declining participation. The cohort was 94% female, had an average age of 60.5 years, and average follow-up of 46 years. In bivariate analysis, PI-LL was the only spinal-pelvic parameter which statistically discriminated between patients doing well and not, as assessed by the Oswestry Disability Index and the PROMIS Pain Interference and Fatigue instruments. In multivariable analysis, (PI-LL > 9°) was associated with worse scores in PROMIS-Pain Interference, Physical Function, Depression, Fatigue, Social Function as well as the total Oswestry score. An SVA > 50 mm was associated with worse scores in the SRS-7. CONCLUSIONS In a cohort of 35 patients with average follow-up of 46 years after posterior spinal instrumentation with Harrington rods (PSIF) for adolescent idiopathic scoliosis, spinal-pelvic mismatch as identified by (PI-LL > 9°) was associated with inferior HRQoL outcomes. Other spinal-pelvic measures (SVA and PT) were not reliably associated with inferior HRQol.Level of Evidence: 4.