Distal adding-on in adolescent idiopathic scoliosis results in diminished health-related quality of life at 10 years following posterior spinal fusion

Purpose The purpose of this study was to investigate associations between the various definitions of adding-on identified in the literature and HRQoL at 10 years following posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS) to identify a clinically relevant definition. Methods In this retrospective cohort study, patients with Lenke type 1 or 2 AIS with 10-year follow-up after PSF were identified in a multicenter registry. Adding-on was identified independently using 5 published definitions and expert spine surgeons' visual confirmation. Worsening of HRQoL was defined as a preoperative to 10-year postoperative decrease in SRS-22 domain score ≥ the minimal clinically important difference (MCID). Results One hundred fifty patients were included, and 118 had HRQoL data available for the main analysis. Worsening pain was noted in 49 (41.5%) patients, appearance in 1 (0.8%), and activity in 70 (59.3%) from preoperative to postoperative. 4 of the 5 definitions of adding-on demonstrated no evidence of association with worsening HRQoL. By Cho's definition (either 1. ≥ 5° increase in Cobb angle AND increase in number of vertebrae in curve distally, or 2. ≥ 5° increase in angulation of 1st disc below LIV), adding-on (27 patients, 22.9%) was associated with an increased risk of worsening pain (59.3% vs. 36.3%, p = 0.033) and activity (77.8% vs. 53.8%, p = 0.026). There was no evidence of association with changes in appearance. Risk of worsening pain and activity was increased by 1.75 and 1.51 times (p = 0.023 and p = 0.002), respectively. Conclusion Cho's definition of adding-on was associated with worsening HRQoL at 10 years following PSF for Lenke type 1 and 2 AIS. Consistent use of this definition will allow us to compare studies and obtain meaningful information in this population. Level of evidence Level II.