1- vs. 2-year follow-up after posterior spinal fusion for AIS: what additional information is gained?

Purpose Traditionally, 2-year follow-up data have been the established standard for reporting clinical outcomes following spinal deformity surgery. However, previous studies indicate that 2-year follow-up does not represent long-term outcomes. Currently, there is no clear data that demonstrate a difference in outcomes between the 1 and 2 years postoperative time-periods following posterior spinal fusions (PSF) for adolescent idiopathic scoliosis (AIS). Methods A multi-center, prospective database was queried for AIS patients treated with PSF. Clinical outcome scores, assessed by SRS-22, coronal and sagittal radiographic parameters were assessed at time periods: 6 months, 1 year, and 2 years post operatively. Complications and reoperation rates were also assessed. Statistical analysis compared outcomes variables across time-points to assess for significant differences. Results 694 patients (82.6% female, mean age at surgery 14.9 ± 2.13 years) were identified. Between post-operative year 1 and 2, significant difference in SRS-22 domain scores were present for function domain (4.5 vs. 4.6; p < 0.001), mental health domain (4.3 vs. 4.2; p < 0.001), and total domain score (4.4 vs. 4.4; p = 0.03) but were below the minimal clinically important difference threshold. New complication development was significantly higher within the first year following surgery than the 1–2 year follow-up period ( p < 0.001) with greater complication severity within the 0–1 year follow-up period ( P = 0.03). Conclusion There are no clinically important changes in SRS-22 domain scores between 1 and 2 years following PSF for AIS, with higher complications in the first year following PSF. Two-year follow-up data provide little added clinical information while under-estimating the cumulative complication and reoperation rates at long-term follow-up.