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 Institutional Review Board approval, medical records and public resources were used to locate patients. Patients completed health-related quality of life (HRQoL) instruments, and returned for assessment including full radiographs. Radiographs were analyzed for scoliosis measures, and recognized spinal-pelvic measures including the lumbar lordosis, sagittal vertical axis (SVA), pelvic incidence, and pelvic tilt (PT). Bivariate and multivariable analyses were performed to assess the association between spinal-pelvic measures and patient-reported outcomes.

RESULTS: Thirty-five of 134 patients agreed to return for complete 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, pelvic incidence and lumbar lordosis difference (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 Patient-reported Outcomes Measurement Information System (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 and the total Oswestry score. An SVA > 50 mm was associated with worse scores in the Scoliosis Research Society-7.

CONCLUSION: In a cohort of 35 patients with average follow-up of 46 years after posterior spinal instrumentation with Harrington rods (PSIF) for AIS, 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.