Background GGS and MCGR are operations aimed to correct and control severe progressive spine deformity while maintaining growth in i-EOS. Past studies yielded similar results between constructs but used vertical coronal measures (e.g. T1-S1), which don’t account for growth outside of plane of measurement due to the spine deformity. This study compares outcomes of GGS and MCGR in i-EOS using 3D-TSL, a validated method that measures spine length in 3D. Methods A multi-center database was queried for patients undergoing MCGR / GGS surgery for i-EOS with minimum 2-year follow-up. 31 GGS and 130 MCGR patients were included with measurements at preop, postop, and 2 years. Mixed-model statistics allowed for missing data points and included age group, intervention type, and visit as fixed factors with subject as random. Growth was calculated with paired values; thus growth numbers may not equal change in average values. Results There were 161 patients (99 female, 61%) whose mean age at surgery was 8.1 yrs. 19.3% GGS and 8.5% MCGR underwent repeat surgeries within the study period. Age, # of instrumented levels, and preop kyphosis/scoliosis were similar between groups. Total cohort mean scoliosis was 70° preop, 38° postop and 41° at final (p<0.001). GGS reduced the major deformity from 67° to 26° (61 % correction), with a 9° loss of correction at 2 years to 35° (46% correction, p=.02). MCGR reduced the major deformity 71° to 40° (37% correction) but did not significantly lose correction (+2°; final 42°, 34% correction) and was not different from GGS at follow-up. GGS maintained kyphosis perioperatively with increase at 2 years (+8°, p=.004), whereas MCGR decreased at postop (-7°, p<.001) with increase of 6° at final (p=.002). Both groups demonstrated T1-S1 height increase from preop (281 mm) to postop (314 mm) and 2-year (336 mm) (p<.001). 3D-TSL didn’t significantly change perioperatively (338 to 342 mm) for either construct. At 2 years GGS 3D-TSL increased 32.6 mm (16.3 /year), while MCGR increased 27.5 mm (13.8/year) (p=.29). Conclusion In i-EOS MCGR and GGS resulted in increase in T1-S1 height preop to postop, but there was no change in 3D-TSL. Postop to Final 3D-TSL identified growth up to 2 years postop in both constructs. T1-S1 height changes suggest that changes in deformity reduce reliability of planar measurements when assessing spine growth. 3D-TSL constitutes a more reliable indicator of spine growth after i-EOS surgery. Overall, GGS and MCGR offer similar outcomes 2 years postop as assessed by 3D- TSL.