<h3>BACKGROUND CONTEXT</h3> Three-column osteotomies (3CO), in the form of pedicle subtraction or vertebral column resection, have become common in adult spinal deformity (ASD) in cases of severe deformity or iatrogenic sagittal malalignment. Although a powerful surgical intervention, 3COs can increase the risks associated with correction. The purpose of this study is to investigate whether more appropriate usage of 3CO is occurring over time. <h3>PURPOSE</h3> To investigate the evolution of 3CO usage. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study of a prospective adult thoracolumbar deformity database. <h3>PATIENT SAMPLE</h3> This study included 762 ASD patients. <h3>OUTCOME MEASURES</h3> Complications, patient-reported outcome measures (ODI, SRS, SF-36). <h3>METHODS</h3> Operative ASD patients (scoliosis >20º, SVA >5cm, PT >25º, or TK >60º) with available baseline and 2-year radiographic and HRQL data were included. Patients were stratified into 2 groups by DOS: Group I (2008-2013) and Group II (2013-2018). Patients who underwent a 3CO in Group I and Group II were then isolated for outcomes analysis. Severe sagittal deformity was defined by a SVA >9.5cm and "match" was defined by meeting ideal age-adjusted alignment. Best clinical outcome (BCO) was defined as ODI <15 and SRS >4.5 as per Smith et al. Univariate, bivariate (BVA) and multivariate analysis (MVA) was used to assess differences in surgical, radiographic, and clinical parameters. <h3>RESULTS</h3> A total of 762 ASD patients met inclusion criteria (59.9yrs±14.0, 79%F, BMI: 27.7 kg/m2 ±6.0, ASD-FI: 3.3±1.6, CCI: 1.8 ±1.7). Controlling for baseline SVA, mismatch, revision status, age, and CCI, Group II was less likely to have a 3CO (.6[.4-.97] compared with Group I (21% vs 31%, both p<0.05). Controlling for age, CCI, and baseline deformity, patients who achieved a match in SVA or PI-LL in Group II showed a lower rate of 3CO (.510[.27-.98], (p<0.05). In an isolated cohort of patients with severe sagittal deformity, controlling for age and CCI showed a lower likelihood of Group II receiving a 3CO (0.5[.3-.94], p<0.05). The following analysis is based solely on patients who had a 3CO from each Group (79 patients in Group I and 59 patients in Group II). MVA controlling for age, deformity, CCI, and invasiveness showed Group II trended towards a higher usage of hooks, tethers, and cement prophylaxis (2[.86-4.7], p=.11), a higher usage of supplemental rods 21.8[7.8- 61], (p=.001), and lower likelihood of PJF 0.23[.07-.76], PJK by 3Y 0.23[.1-.55], rod breakage 0.30[.1-.9], and overall hardware complications 0.28[.1-.8], (all p<0.05). Group II had a lower 2Y ODI and higher SF-36 Mental/Physical/Social/Emotional, SRS Activity/Mental/Pain and SRS-Total, p<0.05. Controlling for BL ODI, Group II was more likely to reach BCO ODI 2.8[1.2-6.4] and SRS 4.6[1.3-16], p<0.05. <h3>CONCLUSIONS</h3> Over a seven-year period, the rates of 3CO usage have declined, including in cases of severe deformity, with an increase in the usage of PJK prophylaxis. A better understanding of the utility of 3CO, along with a greater implementation of preventative measures, has led to a decrease in complications, PJF, PJK, and a significant improvement in patient reported outcome measures. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.